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Shi, H.

Publications and source records attributed to Shi, H..

At least 217 records · Page 12Linked to original sources

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↗

Structural Basis of H2B Ubiquitination-Dependent H3K4 Methylation by COMPASS

The COMPASS complex represents the prototype of the SET1/MLL family of methyltransferases that controls gene transcription by H3K4 methylation (H3K4me). Although H2B monoubiquitination (H2Bub) is well-known as a prerequisite histone mark for COMPASS activity, how the H2Bub-H3K4me crosstalk is catalyzed by COMPASS remains unclear. Here, we report the cryo-EM structures of an extended COMPASS catalytic module (CM) bound to the H2Bub and free nucleosome. The COMPASS CM clamps onto the nucleosome disk-face via an extensive interface to capture the flexible H3 N-terminal tail. The interface also sandwiches a critical Set1 arginine-rich motif (ARM) that auto-inhibits COMPASS. Unexpectedly, without enhancing COMPASS-nucleosome interaction, H2Bub activates the enzymatic assembly by packing against Swd1 and alleviating the inhibitory effect of the Set1 ARM upon fastening it to the acidic patch. By unmasking the spatial configuration of the COMPASS-H2Bub-nucleosome assembly, our studies establish the structural framework for understanding the long-studied H2Bub-H3K4me histone modification crosstalk.

biochemistry↗

DNA mismatches reveal widespread conformational penalties in protein-DNA recognition

Transcription-factor (TF) proteins recognize specific genomic sequences, despite an overwhelming excess of non-specific DNA, to regulate complex gene expression programs1-3. While there have been significant advances in understanding how DNA sequence and shape contribute to recognition, some fundamental aspects of protein-DNA binding remain poorly understood2,3. Many DNA-binding proteins induce changes in the DNA structure outside the intrinsic B-DNA envelope. How the energetic cost associated with distorting DNA contributes to recognition has proven difficult to study and measure experimentally because the distorted DNA structures exist as low-abundance conformations in the naked B-DNA ensemble4-10. Here, we use a novel high-throughput assay called SaMBA (Saturation Mismatch-Binding Assay) to investigate the role of DNA conformational penalties in TF-DNA recognition. The approach introduces mismatched base-pairs (i.e. mispairs) within TF binding sites to pre-induce a variety of DNA structural distortions much larger than those induced by changes in Watson-Crick sequence. Strikingly, while most mismatches either weakened TF binding (~70%) or had negligible effects (~20%), approximately 10% of mismatches increased binding and at least one mismatch was found that increased the binding affinity for each of 21 examined TFs. Mismatches also converted sites from the non-specific affinity range into specific sites, and high-affinity sites into \"super-sites\" stronger than any known canonical binding site. These findings reveal a complex binding landscape that cannot be explained based on DNA sequence alone. Analysis of crystal structures together with NMR and molecular dynamics simulations revealed that many of the mismatches that increase binding induce distortions similar to those induced by TF binding, thus pre-paying some of the energetic cost to deform the DNA. Our work indicates that conformational penalties are a major determinant of protein-DNA recognition, and reveals mechanisms by which mismatches can recruit TFs and thus modulate replication and repair activities in the cell11,12.

biophysics↗

Highly Multiplexed Spatial Mapping of Microbial Communities

Mapping the complex biogeography of microbial communities in situ with high taxonomic and spatial resolution poses a major challenge because of the high density and rich diversity of species in environmental microbiomes and the limitations of optical imaging technology. Here, we introduce High Phylogenetic Resolution microbiome mapping by Fluorescence In-Situ Hybridization (HiPR-FISH), a versatile and cost-effective technology that uses binary encoding and spectral imaging and machine learning based decoding to create micron-scale maps of the locations and identities of hundreds of microbial species in complex communities. We demonstrate the ability of 10-bit HiPR-FISH to distinguish 1023 E. coli strains, each fluorescently labeled with a unique binary barcode. HiPR-FISH, in conjunction with custom algorithms for automated probe design and segmentation of single-cells in the native context of tissues, reveals the intricate spatial architectures formed by bacteria in the human oral plaque microbiome and disruption of spatial networks in the mouse gut microbiome in response to antibiotic treatment. HiPR-FISH provides a framework for analyzing the spatial organization of microbial communities in tissues and the environment at single cell resolution.

microbiology↗

AimB is a small protein regulator of cell size and MreB assembly

The MreB actin-like cytoskeleton assembles into dynamic polymers that coordinate cell shape in many bacteria. In contrast to most other cytoskeletons, few MreB interacting proteins have been well characterized. Here we identify a small protein from Caulobacter crescentus, AimB, as an Assembly Inhibitor of MreB. AimB overexpression mimics inhibition of MreB polymerization, leading to increased cell width and MreB delocalization. Molecular dynamics simulations suggest that AimB binds MreB at its monomer-monomer protofilament interaction cleft. We validate this model through functional analysis of point mutants in both AimB and MreB, photo-crosslinking studies with site-specific unnatural amino acids, and species-specific activity of AimB. Together, our findings indicate that AimB promotes MreB dynamics by inhibiting monomer-monomer assembly interactions, representing a new mechanism for regulating actin-like polymers and the first identification of a non-toxin MreB assembly inhibitor.

microbiology↗

Palmitoylation is critically required for cancer intrinsic PD-1 expression and functions

Programmed cell death protein 1 (PD-1) is a crucial anticancer target, but the relatively low response rate and acquired resistance to existing antibody drugs highlight an urgent need to develop alternative targeting strategies. Here we report the palmitoylation of PD-1, discovered the main DHHC enzyme for this modification, revealed the mechanism for its effect on PD-1 expression, and rationally developed a peptide for targeting PD-1 expression. Palmitoylation promoted the trafficking of PD-1 to recycling endosome, thus preventing its lysosome-dependent degradation. Palmitoylation was required for the activation of PD-1 downstream signaling, and targeting palmitoylation by pharmacological inhibitor or depleting the modification enzyme caused significant anti-tumor effects. A peptide was designed to competitively inhibit PD-1 palmitoylation and expression, opening a new route for developing PD-1 inhibitors as a strategy for cancer immunotherapy.\n\nSignificanceWe show for the first time that PD-1 is palmitoylated, identify DHHC9 as the predominant enzyme for its palmitoylation, and reveal the molecular mechanisms underlying its effects on PD-1 stability and functions. Importantly, we also designed a competitive inhibitor targeting PD-1 palmitoylation, and this first-in-class molecule may inspire the development of new checkpoint inhibitors.

cancer biology↗

Epigenetic regulation of unique genes and repetitive elements by the KRAB zinc finger protein ZFP57

BackgroundKRAB-zinc finger proteins (KZFPs) represent one of the largest families of DNA binding proteins in vertebrate genomes and appear to have evolved to silence transposable elements (TEs) including endogenous retroviruses through sequence-specific targeting of repressive chromatin states. ZFP57 is required to maintain the post-fertilization DNA methylation memory of parental-origin at genomic imprints along with ZFP445 which is specific for imprints. However, ZFP57 has multiple methylated genomic targets. Here we conduct RNA-seq and ChIP-seq analyses in normal and ZFP57 mutant mouse ES cells to understand the relative importance of ZFP57 at unique and repetitive regions of the genome.\n\nResultsOver 80% of ZFP57 targets are TEs, however, ZFP57 is not essential for their repression. The remaining targets lie within unique imprinted and non-imprinted sequences. Though loss of ZFP57 influences imprinted genes as expected, the majority of unique gene targets lose H3K9me3 with little effect on DNA methylation and very few exhibiting alterations in expression. Comparison with DNA methyltransferase-deleted ES cells (TKO) identifies remarkably similar losses of H3K9me3 and changes in expression, defining regions where H3K9me3 is secondary to DNA methylation. We show that ZFP57 is the principal methylation-sensitive KZFP recruiting KAP1 and H3K9me3 in ES cells. Finally, like imprints, other unique targets of ZFP57 are enriched for germline-derived DNA methylation including oocyte-specific methylation that is resistant to post-fertilisation epigenetic reprogramming.\n\nConclusionOur analyses suggest the evolution of a rare DNA methylation-sensitive KZFP that is not essential for repeat silencing, but whose primary function is to maintain DNA methylation and repressive histone marks at germline derived imprinting control regions.

developmental biology↗

Widespread Sexual Dimorphism in the Transcriptome of Human Airway Epithelium in Response to Smoking

Epidemiological studies have shown that female smokers are at higher risk of chronic obstructive pulmonary disease (COPD). Female patients have worse symptoms and health status and increased risk of exacerbations. We determined the differences in the transcriptome of the airway epithelium between males and females at baseline and in response to smoking. We processed public gene expression data of human airway epithelium into a discovery cohort of 211 subjects (never smokers n=68; current smokers n=143) and two replication cohorts of 104 subjects (21 never, 52 current, and 31 former smokers) and 238 subjects (99 current and 139 former smokers. We analyzed gene differential expression with smoking status, sex, and smoking-by-sex interaction and used network approaches for modules level analyses. We identified and replicated two differentially expressed modules between the sexes in response to smoking with genes located throughout the autosomes and not restricted to sex chromosomes. The two modules were enriched in autophagy (up-regulated in female smokers) and response to virus and type 1 interferon signaling pathways which were down-regulated in female smokers compared to males. The results offer insights into the molecular mechanisms of the sexually dimorphic COPD risk and presentation potentially enabling a precision medicine approach to COPD.

genomics↗

A decrease in transcription capacity limits growth rate upon translation inhibition

AbstractIn bacterial cells, inhibition of ribosomes by sublethal concentrations of antibiotics leads to a decrease in growth rate despite an increase in ribosome content. The limitation of ribosomal activity results in an increase in the level of expression from ribosomal promoters; this can deplete the pool of RNA polymerase (RNAP) that is available for the expression of non-ribosomal genes. However, the magnitude of this effect remains to be quantified. Here, we use the change in the activity of constitutive promoters with different affinities for RNAP to quantify the change in the concentration of free RNAP. The data are consistent with a significant decrease in the amount of RNAP available for transcription of both ribosomal and non ribosomal genes. Results obtained with different reporter genes reveal an mRNA length dependence on the amount of full-length translated protein, consistent with the decrease in ribosome processivity affecting more strongly the translation of longer genes. The genes coding for the {beta} and {beta} subunits of RNAP are amongst the longest genes in the E. coli genome, while the genes coding for ribosomal proteins are among the shortest genes. This can explain the observed decrease in transcription capacity that favors the expression of genes whose promoters have a high affinity for RNAP, such as ribosomal promoters.\n\nImportanceExposure of bacteria to sublethal concentrations of antibiotics can lead to bacterial adaptation and survival at higher doses of inhibitors, which in turn can lead to the emergence of antibiotic resistance. The presence of sublethal concentrations of antibiotics targeting translation results in an increase in the amount of ribosomes per cell and a decrease in the cells growth rate. In this work, we have found that inhibition of ribosome activity can result in a decrease in the amount of free RNA polymerase available for transcription, thus limiting the protein expression rate via a different pathway than what was expected. This result can be explained by our observation that long genes, such as those coding for RNA polymerase subunits, have a higher probability of premature translation termination in the presence of ribosome inhibitors, while expression of short ribosomal genes is affected less, consistent with their increased concentration.

microbiology↗

Gut-innervating nociceptor neurons protect against enteric infection by modulating the microbiota and Peyer’s patch microfold cells

Gut-innervating nociceptor sensory neurons respond to noxious/tissue-damaging stimuli by initiating protective responses and releasing mediators that regulate tissue inflammation, gastrointestinal secretion, and motility. The role of nociceptors in host defense against enteric pathogens is unclear. Here, we found that gut-extrinsic nociceptor neurons are critical in protecting the host against Salmonella typhimurium (STm) infection. Nociceptors responded to STm by releasing the neuropeptide calcitonin gene-related peptide (CGRP). Targeted depletion of Nav1.8 and TRPV1 neurons from gut-extrinsic dorsal root ganglia and vagal ganglia increased STm colonization, invasion, and dissemination. Nociceptors regulated the gut microbiota at homeostasis, specifically segmented filamentous bacteria (SFB) levels in the ileum, which protected against STm by colonization resistance. Nociceptors also regulated the density of microfold epithelial cells in the Peyers patch via CGRP to limit points of entry for STm invasion into host tissues. Understanding how host sensory neurons crosstalk with pathogenic bacteria may impact treatments for enteric infections.\n\nHIGHLIGHTSO_LINav1.8 and TRPV1 nociceptors defend against Salmonella typhimurium (STm) infection\nC_LIO_LINociceptors shape the gut microbiota and SFB levels which resist pathogen colonization\nC_LIO_LINociceptors suppress Peyers patch microfold cell density to limit pathogen invasion\nC_LIO_LINeurons sense STm and release CGRP to modulate microfold cells and host defense\nC_LI

immunology↗

A novel QTL conferring Fusarium crown rot resistance located on chromosome arm 6HL in barley

Fusarium crown rot (FCR), caused primarily by Fusarium pseudograminearum, is a devastating disease for cereal production in semi-arid regions worldwide. To identify and characterize loci conferring FCR resistance, we assessed a landrace AWCS799 which is among the top lines identified from a screening. Genetic control of its resistance was investigated by generating and analysing two populations of recombinant inbred lines. One of the populations was used for QTL detection and the other for validation. A novel QTL, located on the long arm of chromosome 6H (designated as Qcrs.caf-6H), was consistently detected in each of the four trials conducted against the mapping population. The QTL explained up to 29.1% of the phenotypic variance and its effect was confirmed in the validation population. Significant interactions between this resistance locus and either plant height or heading date were not detected, further facilitating its manipulation in breeding programs. Key MessageThis study identified and validated a novel and large-effect QTL conferring Fusarium crown rot resistance on the long arm of chromosome 6HL in barley.

plant biology↗

Accurate estimation of SNP-heritability from biobank-scale data irrespective of genetic architecture

The proportion of phenotypic variance attributable to the additive effects of a given set of genotyped SNPs (i.e. SNP-heritability) is a fundamental quantity in the study of complex traits. Recent works have shown that existing methods to estimate genome-wide SNP-heritability often yield biases when their assumptions are violated. While various approaches have been proposed to account for frequency- and LD-dependent genetic architectures, it remains unclear which estimates of SNP-heritability reported in the literature are reliable. Here we show that genome-wide SNP-heritability can be accurately estimated from biobank-scale data irrespective of the underlying genetic architecture of the trait, without specifying a heritability model or partitioning SNPs by minor allele frequency and/or LD. We use theoretical justifications coupled with extensive simulations starting from real genotypes from the UK Biobank (N=337K) to show that, unlike existing methods, our closed-form estimator for SNP-heritability is highly accurate across a wide range of architectures. We provide estimates of SNP-heritability for 22 complex traits and diseases in the UK Biobank and show that, consistent with our results in simulations, existing biobank-scale methods yield estimates up to 30% different from our theoretically-justified approach.

genomics↗

RAISS: Robust and Accurate imputation from Summary Statistics

MotivationMulti-trait analyses using public summary statistics from genome-wide association studies (GWAS) are becoming increasingly popular. A constraint of multi-trait methods is that they require complete summary data for all traits. While methods for the imputation of summary statistics exist, they lack precision for genetic variants with small effect size. This is benign for univariate analyses where only variants with large effect size are selected a posteriori. However, it can lead to strong p-value inflation in multi-trait testing. Here we present a new approach that improve the existing imputation methods and reach a precision suitable for multi-trait analyses.\n\nResultsWe fine-tuned parameters to obtain a very high accuracy imputation from summary statistics. We demonstrate this accuracy for small size-effect variants on real data of 28 GWAS. We implemented the resulting methodology in a python package specially designed to efficiently impute multiple GWAS in parallel.\n\nAvailabilityThe python package is available at: https://gitlab.pasteur.fr/statistical-genetics/raiss, its accompanying documentation is accessible here http://statistical-genetics.pages.pasteur.fr/raiss/.\n\nContacthanna.julienne@pasteur.fr

bioinformatics↗

NAD+ treatment can increase directly the antioxidant capacity of rotenone-treated differentiated PC12 cells

NAD+ administration can produce profound beneficial effects in the animal models of aging and a number of diseases. Since oxidative stress plays key pathological roles in aging and multiple major disorders, it is crucial to elucidate the mechanisms underlying the protective effects of NAD+ administration on oxidative stress-induced cell death. Previous studies have suggested that NAD+ treatment can decrease oxidative cell death indirectly by such mechanisms as preventing mitochondrial permeability transition, while it is unclear if NAD+ administration may decrease oxidative cell death by increasing directly the antioxidant capacity of the cells. Our current study used rotenone-treated differentiated PC12 cells as a cellular model to test our hypothesis that NAD+ treatment may increase directly the antioxidant capacity of the cells exposed to oxidative stress. Our study has indicated that NAD+ treatment can significantly attenuate the rotenone-induced increase in oxidative stress in the cells. Moreover, NAD+ treatment can significantly enhance the GSH/GSSG ratio - a major index of antioxidant capacity - of rotenone-treated cells. Collectively, our study has provided the first evidence indicating that NAD+ treatment can increase directly the antioxidant capacity of cells exposed to oxidative stress. These findings have suggested a novel mechanism underlying the profound protective effects of NAD+ administration in numerous disease models: NAD+ administration can decrease oxidative stress-induced cell death by enhancing directly the antioxidant capacity of the cells. Our finding has also highlighted the nutritional potential of NAD+.

cell biology↗

SIRT2, ERK and Nrf2 mediate NAD+ treatment-induced increase in the antioxidant capacity of differentiated PC12 cells under basal conditions

NAD+ administration is highly beneficial in numerous models of diseases and aging. It is becoming increasingly important to determine if NAD+ treatment may increase directly the antioxidant capacity of cells under basal conditions. In current study we tested our hypothesis that NAD+ can enhance directly antioxidant capacity of cells under basal conditions by using differentiated PC12 cells as a cellular model. We found that NAD+ treatment can increase the GSH/GSSG ratios in the cells under basal conditions. NAD+ can also increase both the mRNA and protein level of {gamma}-glutamylcysteine ligase - a key enzyme for glutathione synthesis, which appears to be mediated by the NAD+-induced increase in Nrf2 activity. These NAD+-induced changes can be prevented by both SIRT2 siRNA and the SIRT2 inhibitor AGK2. The NAD+-induced changes can also be blocked by the ERK signaling inhibitor U0126. Moreover, the NAD+-induced ERK activation can be blocked by both SIRT2 siRNA and AGK2. Collectively, our study has provided the first evidence that NAD+ can enhance directly the antioxidant capacity of the cells under basal conditions, which is mediated by SIRT2, ERK, and Nrf2. These findings have suggested not only the great nutritional potential of NAD+, but also a novel mechanism underlying the protective effects of the NAD+ administration in the disease models: The NAD+ administration can enhance the resistance of the normal cells to oxidative insults by increasing the antioxidant capacity of the cells.

cell biology↗

Seasonal diets overwhelm host species in shaping the gut microbiota of Yak and Tibetan sheep

Host genetics and environmental factors can both shaping composition of gut microbiota, yet which factors are more important is still under debating. Yak (Bos grunniens) and Tibetan sheep (Ovis aries) are very different from the size and genetics. Nomadic Tibetan people keep them as main livestock and feeding them with same grazing systems, which provide a good opportunity to study the effects of diet and host species on gut microbiome. We collected fecal samples from yaks and Tibetan sheeps at different seasons when they were feed with different diets. Illumina data showed that major bacterial phyla of both animals are Bacteroidetes and Firmicutes, which agree with the previous reports. And the season effect had a higher impact on the gut microbiota than that of host species, though the animals are taxonomically distinguished each other at subfamily level. Since that the animal grazing differently at different seasons, this study indicated that diet can trump the host genetics even at higher taxonomic level. This finding provides a cautionary note for the researchers to link host genetics to the composition and function of the gut microbiota.\n\nImportanceYak and Tibetan sheep are very different from the size and genetics (from different sub-family). Nomadic Tibetan people keep them as main livestock and feeding them with same grazing systems, which provide a good opportunity to study the effects of diet and host species on the gut microbiota. Results indicated that diet can trump the host genetics even at higher taxonomic level. This finding provides a cautionary note for the researchers to link host genetics to the composition and function of the gut microbiota.

ecology↗

Chiral twisting in cytoskeletal polymers regulates filament size and orientation

While cytoskeletal proteins in the actin family are structurally similar, as filaments they act as critical components of diverse cellular processes across all kingdoms of life. In many rod-shaped bacteria, the actin homolog MreB directs cell-wall insertion and maintains cell shape, but it remains unclear how structural changes to MreB affect its physiological function. To bridge this gap, we performed molecular dynamics simulations for Caulobacter crescentus MreB and then utilized a coarse-grained biophysical model to successfully predict MreB filament properties in vivo. We discovered that MreB double protofilaments exhibit left-handed twisting that is dependent on the bound nucleotide and membrane binding; the degree of twisting determines the limit length and orientation of MreB filaments in vivo. Membrane binding of MreB also induces a stable membrane curvature that is physiologically relevant. Together, our data empower the prediction of cytoskeletal filament size from molecular dynamics simulations, providing a paradigm for connecting protein filament structure and mechanics to cellular functions.

biophysics↗

AIDE: annotation-assisted isoform discovery and abundanceestimation from RNA-seq data

Genome-wide accurate identification and quantification of full-length mRNA isoforms is crucial for investigating transcriptional and post-transcriptional regulatory mechanisms of biological phenomena. Despite continuing efforts in developing effective computational tools to identify or assemble full-length mRNA isoforms from second-generation RNA-seq data, it remains a challenge to accurately identify mRNA isoforms from short sequence reads due to the substantial information loss in RNA-seq experiments. Here we introduce a novel statistical method, AIDE (Annotation-assisted Isoform DiscovEry), the first approach that directly controls false isoform discoveries by implementing the testing-based model selection principle. Solving the isoform discovery problem in a stepwise and conservative manner, AIDE prioritizes the annotated isoforms and precisely identifies novel isoforms whose addition significantly improves the explanation of observed RNA-seq reads. We evaluate the performance of AIDE based on multiple simulated and real RNA-seq datasets followed by a PCR-Sanger sequencing validation. Our results show that AIDE effectively leverages the annotation information to compensate the information loss due to short read lengths. AIDE achieves the highest precision in isoform discovery and the lowest error rates in isoform abundance estimation, compared with three state-of-the-art methods Cufflinks, SLIDE, and StringTie. As a robust bioinformatics tool for transcriptome analysis, AIDE will enable researchers to discover novel transcripts with high confidence.

bioinformatics↗