Biology subjects

Chen, X.

Publications and source records attributed to Chen, X..

At least 1,423 records · Page 79Linked to original sources

bioRxiv2019

Reproducible observations revealing patterns of the default mode network underlie rumination

Rumination is a repetitive self-referential thinking style and posited to be an expression of abnormalities in the default mode network (DMN) in major depressive disorder (MDD). Recent evidences indicate DMN is not a unitary network but can be further divided into 3 functionally heterogenous subsystems. However, the subsystem mechanism through which DMN underlie rumination remain unclear. Here, with a modified continuous state-like paradigm, we induced healthy participants to ruminate or imagine objective scenarios (as a distraction control condition) on 3 different MRI scanners. We compared functional connectivities (FC) and inter-subject correlations (ISC) of the DMN and its 3 subsystems between rumination and distraction states. Results yielded a highly reproducible and dissociated pattern. During rumination, within-DMN FC was generally decreased compared to the distraction state. At the subsystem level, we found increased FC between the core and medial temporal lobe (MTL) subsystem and decreased FC between the core and dorsal medial prefrontal cortex (DMPFC) subsystem and within the MTL subsystem. Furthermore, we found decreased ISC within the MTL subsystem. These results suggest a specific and less synchronous activity pattern of DMN during rumination and shed new light on the association between rumination and DMN substrates regarding MDD.

neuroscience↗

bioRxiv2019

In vivo nuclear RNA structurome reveals RNA-structure regulation of mRNA processing in plants

mRNA processing is critical for gene expression. A challenge in regulating mRNA processing is how to recognize the actual mRNA processing sites, such as splice and polyadenylation sites, when the sequence content is insufficient for this purpose. Previous studies suggested that RNA structure affects mRNA processing. However, the regulatory role of RNA structure in mRNA processing remains unclear. Here, we performed in vivo selective 2-hydroxyl acylation analysed by primer extension (SHAPE) chemical profiling on Arabidopsis nuclear RNAs and generated the in vivo nuclear RNA structure landscape. We found that nuclear mRNAs fold differently from cytosolic mRNAs. Notably, we discovered a two-nucleotide single-stranded RNA structure feature upstream of 5 splice sites that is strongly associated with splicing and the selection of alternative 5 splice sites. Moreover, we found the single-strandedness of branch point is also associated with 3 splice site recognition. We also identified an RNA structure feature comprising two close-by single-stranded regions that is specifically associated with both polyadenylation and alternative polyadenylation events. Our work demonstrates an RNA structure regulatory mechanism for mRNA processing.

plant biology↗

bioRxiv2019

Dual indexed design of in-Drop single-cell RNA-seq libraries improves sequencing quality and throughput

The increasing demand of single-cell RNA-sequencing (scRNA-seq) experiments, such as the number of experiments and cells queried per experiment, necessitates higher sequencing depth coupled to high data quality. New high-throughput sequencers, such as the Illumina NovaSeq 6000, enables this demand to be filled in a cost-effective manner. However, current scRNA-seq library designs present compatibility challenges with newer sequencing technologies, such as index-hopping, and their ability to generate high quality data has yet to be systematically evaluated. Here, we engineered a new dual-indexed library structure, called TruDrop, on top of the inDrop scRNA-seq platform to solve these compatibility challenges, such that TruDrop libraries and standard Illumina libraries can be sequenced alongside each other on the NovaSeq. We overcame the index-hopping issue, demonstrated significant improvements in base-calling accuracy, and provided an example of multiplexing twenty-four scRNA-seq libraries simultaneously. We showed favorable comparisons in transcriptional diversity of TruDrop compared with prior library structures. Our approach enables cost-effective, high throughput generation of sequencing data with high quality, which should enable more routine use of scRNA-seq technologies.

molecular biology↗

bioRxiv2019

A Synthetic Biology Approach to Sequential Stripe Patterning and Somitogenesis

Reaction-diffusion (RD) based clock and wavefront model has long been proposed as the mechanism underlying biological pattern formation of repeated and segmented structures including somitogenesis. However, systematic molecular level understanding of the mechanism remains elusive, largely due to the lack of suitable experimental systems to probe RD quantitatively in vivo. Here we design a synthetic gene circuit that couples gene expression regulation (reaction) with quorum sensing (diffusion) to guide bacterial cells self-organizing into stripe patterns at both microscopic and colony scales. An experimentally verified mathematical model confirms that these periodic spatial structures are emerged from the integration of oscillatory gene expression as the molecular clock and the outward expanding diffusions as the propagating wavefront. Furthermore, our paired model-experiment data illustrate that the RD-based patterning is sensitive to initial conditions and can be modulated by external inducers to generate diverse patterns, including multiple-stripe pattern, target-like pattern and ring patterns with reversed fluorescence. Powered by our synthetic biology setup, we also test different topologies of gene networks and show that network motifs enabling robust oscillations are foundations of sequential stripe pattern formation. These results verified close connections between gene network topology and resulting RD driven pattern formation, offering an engineering approach to help understand biological development.

synthetic biology↗

bioRxiv2019

PTP-MEG2 regulates quantal size and fusion pore opening through two distinct structural bases and substrates

Tyrosine phosphorylation of secretion machinery proteins is a crucial regulatory mechanism for exocytosis. However, the participation of protein tyrosine phosphatases (PTPs) in different exocytosis stages has not been defined. Here we demonstrated that PTP-MEG2 controls multiple steps of catecholamine secretion. Biochemical and crystallographic analyses revealed key residues that the interactions between govern the PTP-MEG2 and NSF-pY83 site, specify PTP-MEG2 substrate selectivity and modulate the fusion of catecholamine-containing vesicles. Unexpectedly, delineation of PTP-MEG2 mutants along with the NSF binding interface revealed that PTP-MEG2 controls the fusion pore opening through non-NSF dependent mechanisms. Utilizing bioinformatics search and biochemical and electrochemical screening approaches, we discovered that PTP-MEG2 regulates the opening and extension of the fusion pore by dephosphorylating the DYNAMIN2-pY125 and MUNC18-1-pY145 site. Further structural and biochemical analysis confirmed the interaction of PTP-MEG2 with MUNC18-1-pY145 or DYNAMIN2-pY125 through a distinct structural basis compared with that of the NSF-pY83 site. Our studies extended mechanistic insights in complex exocytosis processes. HIGHLIGHTSPTP-MEG2 regulates multiple steps of exocytosis. A crystal structure of the PTP-MEG2/phosphor-NSF-pY83 segment was obtained. Functional delineation of the PTP-MEG2/NSF interface led to the discovery of new PTP-MEG2 substrates. PTP-MEG2 regulates fusion pore opening and extension through the DYNAMIN2-pY125 site and MUNC18-1 pY145 site. The distinct structural basis of the recognition of substrates by PTP-MEG2 allows selective inhibitor design.

cell biology↗

bioRxiv2019

Bone morphogenetic protein 9 induces osteogenic differentiation of germ cell 1 spermatogonial cells

Germ cell 1 spermatogonial (GC-1spg) cells are multipotent progenitor cells. We previously confirmed that bone morphogenetic protein (BMP) 9 is among the most osteogenic BMPs. However, whether GC-1spg cells are driven toward osteogenic differentiation under proper stimuli is uncertain. Additionally, the molecular mechanism of BMP9 remains unclear. In the present study, we aimed to determine whether BMP9 can induce osteogenic differentiation of GC-1spg cells. Recombinant adenoviruses were generated by the AdEasy system to regulate the BMP9 expression in GC-1spg cells. We identified osteogenic markers by real-time PCR and staining techniques in vitro. Ectopic ossification assays and histological analysis were also performed to verify the in vivo activity of BMP9. Finally, potential signaling pathways of BMP9 were assessed by transcriptome sequencing and KEGG enrichment analysis. Using recombinant adenoviruses, we demonstrate that BMP9 upregulates osteogenic markers including Runx2, osteocalcin, osteopontin, and Sox9. BMP9 also activates alkaline phosphatase activity and calcium deposition in GC-1spg cells. In vivo results show that BMP9 overexpression in GC-1spg cells promotes ectopic bone formation and chondrogenesis. In addition, RNA-sequencing and KEGG pathway analysis demonstrate that several signaling pathways are involved in BMP9-mediated osteogenesis. GC-1spg cells not only maintain spermatogenesis but also retain the ability to form bone tissue. Therefore, BMP9 activity in GC-1spg cells may help identify signaling pathways implicated in bone formation and could be of use in regenerative medicine.

cell biology↗

bioRxiv2019

Regulation of FXR1 by alternative splicing is required for muscle development and controls liquid-like condensates in muscle cells

Fragile-X mental retardation autosomal homolog-1 (FXR1) is a muscle-enriched RNA-binding protein. FXR1 depletion is perinatally lethal in mice, Xenopus, and zebrafish; however, the mechanisms driving these phenotypes remain unclear. The FXR1 gene undergoes alternative splicing, producing multiple protein isoforms and mis-splicing has been implicated in disease. Furthermore, mutations that cause frameshifts in muscle-specific isoforms result in congenital multi-minicore myopathy. We observed that FXR1 alternative splicing is pronounced in the serine and arginine-rich intrinsically-disordered domain; these domains are known to promote biomolecular condensation. Here, we show that tissue-specific splicing of fxr1 is required for Xenopus development and alters the disordered domain of FXR1. FXR1 isoforms vary in the formation of RNA-dependent biomolecular condensates in cells and in vitro. This work shows that regulation of tissue-specific splicing can influence FXR1 condensates in muscle development and how mis-splicing promotes disease.\n\nHIGHLIGHTSO_LIThe muscle-specific exon 15 impacts FXR1 functions\nC_LIO_LIAlternative splicing of FXR1 is tissue- and developmental stage specific\nC_LIO_LIFXR1 forms RNA-dependent condensates\nC_LIO_LISplicing regulation changes FXR1 condensate properties\nC_LI

cell biology↗

bioRxiv2019

Multi-level analysis of reproduction in an Antarctic midge identifies female and male accessory gland products that are altered by larval stress and impact progeny viability

The Antarctic midge, Belgica antarctica, is a wingless, non-biting midge endemic to Antarctica. Larval development requires at least two years, but adult life lasts only two weeks. The nonfeeding adults mate in swarms and females die shortly after oviposition. Eggs are suspended in a gel of unknown composition that is expressed from the female accessory gland. This project characterizes molecular mechanisms underlying reproduction in this midge by examining differential gene expression in whole males, females, and larvae, as well as in male and female accessory glands. Functional studies were used to assess the role of the gel encasing the eggs, as well as the impact of stress on reproductive biology. RNA-seq analyses revealed sex- and development-specific gene sets along with those associated with the accessory glands. Proteomic analyses were used to define the composition of the egg-containing gel, which is generated during multiple developmental stages and derived from both the accessory gland and other female organs. Functional studies indicate the gel provides a larval food source and thermal and dehydration buffer, all of which are critical for viability. Larval dehydration stress directly reduces production of storage proteins and key accessory gland components, a feature that impacts adult reproductive success. Modeling reveals that bouts of dehydration may significantly impact population growth. This work lays a foundation for further examination of reproduction in midges and provides new information related to general reproduction in dipterans. A key aspect is that reproduction and stress dynamics, currently understudied in polar organisms, are likely to prove critical for determining how climate change will alter survivability.

genomics↗

bioRxiv2019

Golden pompano genome and embryo transcriptome shed light on regulation of minor ZGA gene on heart and vascular development

BACKGROUNDAngiogenesis is closely associated with angiogenesis-dependent diseases including cancers and ocular diseases. Anti-angiogenic therapeutics have been focusing on the (VEGF)/VEGFR signaling axis. However, the clinical resistance, high cost and frequent administration of anti-VEGF drugs make it urgent to discover novel angiogenic pathways.VE-PTP (ptprb) is a novel target with great anti-angiogenic potential. However, it is unclear whether upstream signaling pathways targeting VE-PTP exist in angiogenesis. METHODSWhole genome and embryo transcriptome sequencing were applied to discover the new gene nxhl. Transgenic zebrafish model, morpholino knockdown and small interfering RNA were used to explore the role of nxhl in angiogenesis both in vitro and in vivo. RNA pulldown, RIP and ChIRP-MS were used to identify interactions between RNA and protein. RESULTSWe discovered a novel zebrafish gene nxhl which is a homologue of the conserved gene nxh that co-expressed with some key genes essential for embryo development in vertebrate. Nxhl deletion causes angiogenesis defects in embryo. Moreover, nxhl is essential to mediate effects of angiogenesis in vivo and in vitro, and ptprb depletion duplicates the phenotypes of nxhl deficiency. Importantly, nxhl acts upstream of ptprb and regulates many extreme important ptprb-linked angiogenic genes by targeting VE-PTP (ptprb) through interactions with NCL. Notably, nxhl deletion decreases the phosphorylation of NCL T76 and increases the acetylation of NCL K88, suggesting nxhl may regulate downstream VE-PTP signaling pathways by mediation of NCL posttranslational modification. This is the first description of the interaction between nxhl and NCL, NCL and VE-PTP (ptprb), uncovering a novel nxhl-NCL-VE-PTP signaling pathway on angiogenesis regulation. CONCLUSIONSOur study identifies nxhl controlling angiogenesis by targeting VE-PTP through interactions with NCL, uncovering novel upstream controllers of VE-PTP. This nxhl-NCL-VE-PTP pathway may be a therapeutic target in the treatment of angiogenesis-dependent diseases. Clinical PerspectiveO_ST_ABSWhat Is New?C_ST_ABSO_LIWe report a novel nxhl-NCL-VE-PTP signaling pathway that controls angiogenesis. C_LIO_LIWe for the first time demonstrate that nxhl interacts with NCL which simultaneously binds to VE-PTP that plays key roles on EC adherens junction, integrity and vascular homeostasis. C_LIO_LINxhl also controls some other crucial VE-PTP-linked downstream angiogenic genes (such as Tie2, VEGFaa, VEGFR2, Erbb2, S1pr1 and Hey2) which explain the phenotypes induced by the nxhl deficiency. C_LIO_LIOur study indicates the key role of nxhl on controlling angiogenesis as an upstream regulator of VE-PTP. C_LI What Are the Clinical Implications?O_LIThere are several ongoing researches investigating the utility of VE-PTP or NCL inhibitors on treatment of angiogenesis-dependent diseases including a range of cancers and nonneoplastic diseases, such as AMD, DME, RA and atherosclerosis. C_LIO_LITargeting the nxhl-NCL-VE-PTP pathway may facilitate therapeutic angiogenesis in patients with cancers or ocular diseases such as DME. C_LIO_LIOur study highlights the great potential of nxhl on anti-angiogenic therapeutics by targeting VE-PTP. C_LI

genomics↗

bioRxiv2019

Pseudomonas aeruginosa lasR mutant fitness in microoxia is supported by an Anr-regulated oxygen-binding hemerythrin

Pseudomonas aeruginosa strains with loss-of-function mutations in the transcription factor are frequently encountered in the clinic and the environment. Among the characteristics common to LasR-defective (LasR-) strains is increased activity of the transcription factor Anr, relative to their LasR+ counterparts, in low oxygen conditions. One of the Anr-regulated genes that was highly induced in the LasR-strains encoded a putative oxygen-binding hemerythrin encoded by PA14_42860 (PA1673) which we named mhr for microoxic hemerythrin. Purified P. aeruginosa Mhr protein contained the predicted di-iron center and binds oxygen with a Kd of 1 {micro}M. Both Anr and Mhr were necessary for fitness in lasR+ and lasR mutant strains in colony biofilms grown in microoxic conditions, and the effects were more striking in the lasR mutant. Among genes in the Anr regulon, mhr was most closely co-regulated with the Anr-controlled high affinity cytochrome c oxidase genes and in the absence of high affinity cytochrome c oxidase activity, deletion of mhr no longer caused a fitness disadvantage suggesting that Mhr works in concert with microoxic respiration. We demonstrate that Anr and Mhr contribute to LasR-strain fitness even in the normoxic biofilm conditions, and metabolomics data indicate that in a lasR mutant, expression of Anr-regulated mhr leads to differences in metabolism in cells grown on LB and artificial sputum medium. Together these data indicate that increased Anr activity in microoxically-grown lasR mutants confers an advantage in part for its regulation of the O2 binding protein Mhr.\n\nSignificancePseudomonas aeruginosa, a versatile bacterium that both lives in environmental habitats and causes life-threatening opportunistic infections, uses quorum sensing to coordinate gene expression with cell density. The lasR gene, which encodes a quorum sensing regulator, is often deleteriously mutated in clinical isolates. Interestingly, LasR-strains have high activity of the oxygen-sensitive transcription factor Anr in microoxic conditions. This report identifies and characterizes an Anr-regulated microoxic hemerythrin that reversibly binds oxygen. We showed both anr and mhr are critical to fitness in microoxia, and these genes uniquely benefit LasR-strains in normoxia. Our findings enrich our understanding of the success of P. aeruginosa as a pulmonary resident through its propensity to lose LasR functionality in the context of low-oxygen infection environments.

microbiology↗

bioRxiv2019

The effects of modified sialic acids on mucus and erythrocytes on influenza A virus HA and NA functions

Sialic acids (Sia) are the primary receptors for influenza viruses, and are widely displayed on cell surfaces and in secreted mucus. Sia may be present in variant forms that include O-acetyl modifications at C4, C7, C8, and C9 positions, and N-acetyl or N-glycolyl at C5. They can also vary in their linkages, including 2-3 or 2-6-linkages. Here, we analyzed the distribution of modified Sia in cells and tissues of wild-type mice, or in mice lacking cytidine 5-monophosphate-N-acetylneuraminic acid hydroxylase (CMAH) enzyme that synthesizes N-glycolyl modifications (Neu5Gc). We also examined the variation of Sia forms on erythrocytes and saliva from different animals. To determine the effect of Sia modifications on influenza A virus (IAV) infection, we tested for effects on hemagglutinin (HA) binding and neuraminidase (NA) cleavage. We confirmed that 9-O-acetyl, 7,9-O-acetyl, 4-O-acetyl, and Neu5Gc modifications are widely but variably expressed in mouse tissues, with the highest levels detected in the respiratory and gastrointestinal tracts. Secreted mucins in saliva and surface proteins of erythrocytes showed a great degree of variability in display of modified Sia between different species. IAV HA from different virus strains showed consistently reduced binding to both Neu5Gc and O-acetyl modified Sia; however, while IAV NA were inhibited by Neu5Gc and O-acetyl modifications, there was significant variability between NA types. The modifications of Sia in mucus may therefore have potent effects on the functions of IAV, and may affect both pathogens and the normal flora of different mucosal sites.\n\nIMPORTANCESialic acids (Sia) are involved in many different cellular functions and are receptors for many pathogens. Sia come in many chemically modified forms but we lack a clear understanding of how they alter the interactions with microbes. Here we examine the expression of modified Sia in mouse tissues, on secreted mucus in saliva, and on erythrocytes, including those from IAV host species and animals used in IAV research. These Sia forms varied considerably between different animals, and their inhibitory effects on IAV NA and HA activities and on bacterial sialidases (neuraminidases) suggest a host-variable protective role in secreted mucus.

microbiology↗

bioRxiv2019

Zonation-dependent single-endothelial cell transcriptomic changes in the aged brain

With advances in single-cell genomics, molecular signatures of cells comprising the brain vasculature are revealed in unprecedented detail1,2, yet the ageing-associated cell subtype transcriptomic changes which may contribute to neurovascular dysfunction in neurodegenerative diseases3-7 remain elusive. Here, we performed single-cell transcriptomic profiling of brain endothelial cells (EC) in young adult and aged mice to characterize their ageing-associated genome-wide expression changes. We identified zonation-dependent transcriptomic changes in aged brain EC subtypes, with capillary ECs exhibiting the most transcriptomic alterations. Pathway enrichment analysis revealed altered immune/cytokine signaling in ECs of all vascular segments, while functional changes impacting the blood-brain barrier (BBB) and glucose/energy metabolism were most prominently implicated in ECs of the capillary bed - the primary site where ECs and other neurovascular unit (NVU) cell types closely interact and coordinate to regulate BBB and cerebral blood flow in health and diseased conditions8-17. Furthermore, an overrepresentation of Alzheimers disease (AD)-associated genes identified from GWAS studies was evident among the human orthologs of differentially expressed genes of aged capillary ECs but not other EC subtypes. Importantly, for numerous EC-enriched differentially expressed genes with important functional roles at the BBB and/or association with AD, we found concordant expression changes in human aged or AD brains. Finally, we demonstrated that treatment with exenatide, a glucagon-like peptide-1 receptor (GLP-1R) agonist, strongly reverses transcriptomic changes in ECs and largely reduces BBB leakage in the aged brain. Thus, our study provides insights into detailed transcriptomic alterations underlying brain EC ageing that are complex with subtype specificity yet amenable to pharmacological interventions.

neuroscience↗

bioRxiv2019

Structure of E3 ligase E6AP with a novel proteasome-binding site provided by substrate receptor hRpn10

Regulated proteolysis by the proteasome involves [~]800 enzymes for substrate modification with ubiquitin, of which [~]600 are E3 ligases. We report here that E6AP/UBE3A is distinguished from other ubiquitin E3 ligases by having a 12 nM binding site at the proteasome contributed by substrate receptor hRpn10/PSMD4/S5a. Intrinsically disordered by itself, and previously uncharacterized, this domain in hRpn10 locks into a novel well-defined helical structure to form an intermolecular 4-helix bundle with the E6AP AZUL domain, which is unique to this E3. We thus name the hRpn10 AZUL-binding domain RAZUL. We further find in human cells that loss of RAZUL by CRISPR-based gene editing leads to loss of E6AP at the proteasome, where associated ubiquitin is correspondingly reduced, suggesting that E6AP ubiquitinates substrates at or for the proteasome. Altogether, our findings indicate E6AP to be a privileged E3 for the proteasome, with a dedicated, high affinity binding site contributed by hRpn10.

molecular biology↗

bioRxiv2019

Whole genome sequencing of 358 brown planthoppers uncovers the landscape of their migration and dispersal worldwide

The brown planthopper (BPH), Nilaparvata lugens, is a serious migratory rice pest, which is distributed in the broad area of the tropical and temperate Asian-Pacific region. However, we know little about key aspects regarding its evolution such as how they diverged and dispersed worldwide. By resequencing and analyzing 358 BPH genomes from 92 populations across the world, we uncover the genetic relationships among their worldwide populations and the history of their global dispersal. We recovered five genetic groups representing the major population structures. Of these, Australian BPHs were shown large genetic divergence with Asian BPHs; two distinct groups have formed in South and Southeast/East Asia that show strong genetic admixture in the southwest border regions of China and west Thailand with Myanmar; two local populations in Bangladesh and Fujian province of China, respectively, unexpectedly separated with surrounding populations. We also find the genetic similarity and closely phylogenetic relationships between majority of East Asian BPHs and Indo-china peninsula BPHs, indicating that Southeast Asia mainland is the major insect sources and overwintering sites for East Asia. Our study provides important molecular evidence to address BPH evolution and other key aspects of its biology such as insecticides resistance and rice varieties virulence.

evolutionary biology↗

bioRxiv2019

MYPT1 O-GlcNAcylation Dictates Timely Disjunction of Centrosomes

The role of O-linked N-acetylglucosamine (O-GlcNAc) modification in the cell cycle has been enigmatic. Previously, both O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) disruption have been shown to derail the mitotic centrosome numbers, suggesting that mitotic O-GlcNAc oscillation needs to be in concert with mitotic progression to account for centrosome integrity. Here we attempted to address the underlying molecular mechanism by both chemical approaches and biological assays, and observed that Thiamet-G (OGA inhibitor) incubation strikingly elevated centrosomal distances, suggestive of premature centrosome disjuction. These aberrancies could be overcome by inhibiting Polo-like kinase 1 (Plk1), a mitotic master kinase. Plk1 inactivation is modulated by the Myosin Phosphatase Targeting Subunit 1 (MYPT1)-Protein Phosphatase 1 c{beta} (PP1c{beta}) complex. Interestingly, MYPT1 is abundantly O-GlcNAcylated and the modified residues have been detected in a recent O-GlcNAc profiling screen utilizing chemoenzymatic labeling and bioorthogonal conjugation. We demonstrate that MYPT1 is O-GlcNAcylated at T577, S585, S589 and S601, which antagonizes CDK1-dependent phosphorylation at S473, subsequently attenuating the association between MYPT1 and Plk1, and promoting PLK1 activity. Thus under high O-GlcNAc, Plk1 is untimely activated, conducive to inopportune centrosome separation and disrupting the cell cycle. We propose that too much O-GlcNAc is equally deleterious as too little O-GlcNAc, and a fine balance between the OGT/OGA duo is indispensible for successful mitotic divisions.

biochemistry↗

bioRxiv2019

Selectivity and engineering of the sialoglycan-binding spectrum in Siglec-like adhesins

The Siglec-like Serine-Rich Repeat (SRR) adhesins mediate bacterial attachment to mammalian hosts via sialoglycan receptors. Here, we combine structural, computational, biochemical, and phylogenetic approaches to elucidate the determinants of the sialoglycan-binding spectrum across the family of Siglec-like SRR adhesins. We further identified mutable positions that disproportionately affect sialoglycan selectivity, as demonstrated by increases in binding to alternative ligands of 2- to 3-orders of magnitude. Biologically, these studies highlight how bacteria nimbly modulate the receptor interaction during coevolution of host and pathogen. These studies additionally created binding proteins specific for sialyl-T antigen or 6S-sialyl LewisX that can recognize glycosylation of human plasma proteins. The engineered binding proteins can facilitate the characterization of normal cellular glycan modifications or may be used as diagnostic tools in disease states with altered glycosylation.\n\nSignificanceThe ability of bacteria to bind selectively to host receptors underlies both commensalism and pathogenesis. Here, we identify the molecular basis for receptor selectivity in streptococci that bind to sialoglycan receptors. This revealed how to convert these adhesins into selective probes that measure triand tetrasacharides within the context of larger glycosylations. These probes that can be used in a laboratory with no specialized equipment and can be used to address biological questions relating to sialoglycan-dependent signaling and adhesion.

biochemistry↗

bioRxiv2019

An evaluation model for aboveground biomass Based on Hyperspectral Data from field and TM8 in Khorchin grassland, China

Biomass is an important indicator for monitoring vegetation degradation and productivity. This study tests the applicability of Hyperspectral Remote-Sensing in situ measurements for high-precision estimation aboveground biomass (AGB) on regional scales of Khorchin grassland landscape in Inner Mongolia, China. Field experiments were carried out which collected hyperspectral data with a portable visible/NIR hyperspectral spectrometer (SOC 710), and collected aboveground net primary productivity (ANPP). Ground spectral models were then developed to estimate ANPP from the normalized difference vegetation index (NDVI), which was measured in the field following the same method as that of the Thematic Mapper(TM) from the Landsat 8 land imager (TM_NDVI). Regression analysis was used to assess the relationship between ANPP and NDVI based on coefficients of determination (R2) and error analysis. The estimation of ANPP had unique optimal regression models. By comparing the different spectral inversion models, we selected an exponential model associating ANPP with NDVI (ANPP = 12.523*e3.370*(0.462*TM_NDVI+0.413), standard error = 24.74 g m-2, R2 = 0.636, P < 0.001). This study suggests that the model can be used to monitor the condition and estimate the productivity of grassland at regional scales. The results still show a high potential to map grassland degradation proxies on the ground hyperspectral model. Thus, this study presents biomass hyperspectral inversion technology to remotely detect and monitor grassland degradation and productivity at high precision.

ecology↗

bioRxiv2019

Both Determinants of Allosteric and Active Sites Responsible for Catalytic Activity of Delta 12 Fatty Acid Desaturase by Domain Swapping

Cheese lacks essential fatty acids (EFAs). Delta 12 fatty acid desaturase (FADS12) is a critical enzyme required for EFA biosynthesis in fermentation of the predominant strains of cheese. Previously, we identified the FADS12 gene and characterized its function for the first time in Geotrichum candidum, a dominant strain used to manufacture soft cheese with white rind. In this study, we analyzed the molecular mechanism of FADS12 function by swapping domains from Mortierella alpina and G. candidum that had, respectively, high and low oleic acid conversion rates. The results revealed three regions that are essential to this process, including regions from the end of the second transmembrane domain to the beginning of the third transmembrane domain, from the end of the third transmembrane domain to the beginning of the fourth transmembrane domain, and from the 30-amino acid from the end of the sixth transmembrane domain to the C-terminal end region. Based on our domain swapping analyses, nine pairs of amino acids including H112, S118, H156, Q161, K301, R306, E307, A309 and S323 in MaFADS12 (K123, A129, N167, M172, T302, D307, I308, E310 and D324 in GcFADS12) were identified as having a significantly effect on FADS12 catalytic efficiency, and linoleic acid and its analogues (12,13-cyclopropenoid fatty acid) were found to inhibit the catalytic activity of FADS12 and related recombinant enzymes. Furthermore, the molecular mechanism of FADS12 inhibition was analyzed. The results revealed two allosteric domains, including one domain from the N-terminal region to the beginning of the first transmembrane domain and another from the 31st amino acid from the end of the sixth transmembrane domain to the C terminus. Y4 and F398 amino acid residues from MaFADS12 and eight pairs of amino acids including G56, L60, L344, G10, Q13, S24, K326 and L344 in MaFADS12 (while Y66, F70, F345, F20, Y23, Y34, F327 and F345 in GcFADS12) played a pivotal role in FADS12 inhibition. Finally, we found that both allosteric and active sites were responsible for the catalytic activity of FADS12 at various temperatures, pH, and times. This study offers a solid theoretical basis to develop preconditioning methods to increase the rate at which GcFADS12 converts oleic and linoleic acids to produce higher levels of EFAs in cheese.

molecular biology↗