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Das, K.

Publications and source records attributed to Das, K..

At least 37 records · Page 2Linked to original sources

Structural insights into TRAP association with ribosome-Sec61 complex, and translocon inhibition by a CADA derivative

During co-translational translocation, the signal peptide of a nascent chain binds Sec61 translocon to initiate protein transport through the ER membrane. Our cryo-EM structure of ribosome-Sec61 shows binding of an ordered heterotetrameric TRranslocon-Associated Protein (TRAP) complex, in which TRAP-{gamma} is anchored at two adjacent positions of 28S rRNA and interacts with ribosomal protein L38 and Sec61/{gamma}. Four transmembrane helices (TMHs) of TRAP-{gamma} cluster with one C-terminal helix of each , {beta}, and {delta} subunits. The seven TMH bundle helps position a crescent-shaped trimeric TRAP-/{beta}/{delta} core in the ER lumen, facing the Sec61 channel. Further, our in vitro assay establishes the CADA derivative CK147 as a translocon inhibitor. A structure of ribosome-Sec61-CK147 reveals CK147 binding the channel and interacting with the plug helix from the lumenal side. The CK147-resistance mutations surround the inhibitor. These structures help in understanding the TRAP functions and provide a new Sec61 site for designing translocon inhibitors. Short SummaryCryo-EM structures reveal TRAP binding to ribosome-Sec61 complex, and CK147 inhibiting Sec61 by arresting the plug helix inside the channel.

cell biology↗

Yeast Mitochondrial Derived Vesicles (MDVs) have membrane potential and contain a functional ATP synthase

Vesicular transport is a means of communication. While cells can communicate between each other via secretion of extracellular vesicles, less is known regarding organelle-to organelle communication, in particularly in the case of mitochondria. Mitochondria are responsible for the production of energy and for essential metabolic pathways in the cell, as well as fundamental processes such as apoptosis and aging. Here we show that functional mitochondria, isolated from Saccharomyces cerevisiae release vesicles, independent of the fission machinery. We were then able for the first time to isolate these Mitochondrial Derived Vesicles (MDVs) and found that they are relatively uniform in size, of about 100nm and carry selective protein cargo including enrichment of ATP synthase subunits. Remarkably, we further found that these MDVs harbor a functional ATP synthase complex. Moreover, we demonstrate that these vesicles have a membrane potential, produce ATP, and seem to fuse with naive mitochondria. Our findings reveal a possible delivery mechanism of ATP producing vesicles, which can potentially regenerate ATP deficient mitochondria and may participate in organelle to organelle communication.

cell biology↗

Ubiquitination occurs in the mitochondrial matrix byeclipsed targeted components of the ubiquitin machinery

Ubiquitination is a critical type of post translational modification in eukaryotic cells. It is involved in regulating nearly all cellular processes in the cytosol and nucleus. Mitochondria, known as the metabolism heart of the cell, are organelles that evolved from bacteria. Using the subcellular compartment-dependent -complementation, we detect multiple components of ubiquitination machinery as being eclipsed distributed to yeast mitochondria. Subsequently, the results with respect to MTS (mitochondrial targeting sequence) targeted HA-tagged ubiquitin demonstrate that certain ubiquitination events specifically occur in yeast mitochondria and are independent of proteasome activity in the cytosol/nucleus. Importantly, we show that the E2 Rad6 affects the pattern of protein ubiquitination in mitochondria and provides an in vivo assay for its activity in the matrix of the organelle. This study shows that ubiquitination occurs in the mitochondrial matrix by eclipsed targeted components of the ubiquitin machinery, providing a new perspective of mitochondrial and ubiquitination research.

cell biology↗

Cryo-EM structures of Doravirine and Rilpivirine with HIV-1 Reverse Transcriptase/DNA Aptamer: Nonnucleoside Inhibitor Resistance by E138K and M184I Mutations

Structures trapping a verity of functional and conformational states of HIV-1 reverse transcriptase (RT) have been determined by X-ray crystallography. These structures have played important roles in understanding the mechanisms of catalysis, inhibition and drug resistance, and in driving drug design. However, structures of several desired complexes of RT could not be obtained even after many crystallization or crystal soaking experiments. The ternary complexes of doravirine and rilpivirine with RT/DNA are such examples. Structural study of HIV-1 RT by single-particle cryo-EM has been challenging due to the enzymes relatively smaller size and higher flexibility. We optimized a protocol for rapid structure determination of RT complexes by cryo-EM and determined six structures of wild-type and E138K/M184I mutant RT/DNA in complexes with the nonnucleoside inhibitors rilpivirine, doravirine, and nevirapine. RT/DNA/rilpivirine and RT/DNA/doravirine complexes have structural differences between them and from the representative conformation of RT/DNA/nevirapine (or efavirenz); the primer grip in the RT/DNA/doravirine and the YMDD motif in the RT/DNA/rilpivirine complexes have large shifts. The DNA primer 3-end in the doravirine-bound structure is positioned at the active site, but the complex is in a non-productive state. In the mutant RT/DNA/rilpivirine structure, I184 is stacked with the DNA such that their relative positioning can influence rilpivirine in the pocket. Simultaneously, E138K mutation widens the NNRTI-binding pocket entrance, potentially contributing to a faster rate of rilpivirine dissociation by E138K/M184I mutant RT, as reported by earlier kinetic studies. These structural differences have implications for drug design and for understanding molecular mechanisms of drug resistance.

biophysics↗

Intramuscular mRNA BNT162b2 vaccine against SARS-CoV-2 induces robust neutralizing salivary IgA

Intramuscularly administered vaccines stimulate robust serum neutralizing antibodies, yet they are often less competent in eliciting sustainable sterilizing immunity at the mucosal level. Our study uncovers, strong neutralizing mucosal component (NT50 [≤] 50pM), emanating from intramuscular administration of an mRNA vaccine. We show that saliva of BNT162b2 vaccinees contains temporary IgA targeting the Receptor-Binding-Domain (RBD) of SARS-CoV-2 spike protein and demonstrate that these IgAs are key mediators of potent neutralization. RBD-targeting IgAs were found to associate with the Secretory Component, indicating their bona-fide transcytotic origin and their dimeric tetravalent nature. The mechanistic understanding of the exceptionally high neutralizing activity provided by mucosal IgA, acting at the first line of defence, will advance vaccination design and surveillance principles, pointing to novel treatment approaches, and to new routes of vaccine administration and boosting. Significance statementWe unveiled powerful mucosal neutralization upon BNT162b2 vaccination, mediated by temporary polymeric IgA and explored its longitudinal properties. We present a model, whereby the molecular architecture of polymeric mucosal IgA and its spatial properties are responsible for the outstanding SARS-CoV-2 neutralization potential. We established a methodology for quantitative comparison of immunoreactivity and neutralization for IgG and IgAs in serum and saliva in molar equivalents for standardization in diagnostics, surveillance of protection and for vaccine evaluations.

microbiology↗

Sliding of HIV-1 reverse transcriptase over DNA creates a transient P pocket - Targeting P-pocket by fragment screening

HIV-1 reverse transcriptase (RT) slides over an RNA/DNA or dsDNA substrate while copying the viral RNA to a proviral DNA. We report a crystal structure of RT/dsDNA complex in which RT overstepped the primer 3-end of a dsDNA substrate and created a transient P-pocket at the priming site. We performed a high-throughput screening of 300 drug-like fragments by X-ray crystallography and identified binding of two to P-pocket, which is composed of structural elements from polymerase active site, primer grip, and template-primer that are resilient to drugresistance mutations. Analogs of a fragment were synthesized of which two showed noticeable RT inhibition. An engineered RT/DNA aptamer complex trapped the transient P-pocket in solution. Structures of the RT/DNA complex were determined with a fragment and a synthesized analog bound at P-pocket by single-particle cryo-EM. Identification of P-pocket and the devised structurebased platform provide an opportunity for designing new types of polymerase inhibitors.

biophysics↗

3'-Sulfated Lewis A is a Biomarker for Metaplastic and Oncogenic Transformation of Several Gastrointestinal Epithelia

IntroductionMultiple previous studies have shown the monoclonal antibody Das-1 (formerly called 7E12H12) specifically recognizes metaplastic and carcinomatous lesions in multiple organs of the gastrointestinal system (e.g. Barretts esophagus, intestinal-type metaplasia of the stomach, gastric adenocarcinoma, high-grade pancreatic intraepithelial neoplasm, and pancreatic ductal adenocarcinoma) as well as in other organs (bladder and lung carcinomas). Beyond being a useful biomarker in tissue, mAb Das-1 has recently proven to be more accurate than current paradigms for identifying cysts harboring advanced neoplasia. Though this antibody has been used extensively for clinical, basic science, and translational applications for decades, its epitope has remained elusive. MethodsIn this study, we chemically deglycosylated a standard source of antigen, which resulted in near complete loss of the signal as measured by western blot analysis. The epitope recognized by mAb Das-1 was determined by affinity to a comprehensive glycan array and validated by inhibition of a direct ELISA. ResultsThe epitope recognized by mAb Das-1 is 3-Sulfo-Lewis A (3-Sulfo-LeA). 3-Sulfo-LeA is broadly reexpressed across numerous GI epithelia and elsewhere only after metaplastic and carcinomatous transformation. Discussion3-Sulfo-LeA is a clinically important antigen that can be detected both intracellularly in tissue using immunohistochemistry and extracellularly in cyst fluid and serum by ELISA. The results open new avenues for tumorigenic risk stratification of various gastrointestinal lesions.

cancer biology↗

Crystal structure of prototype foamy virus (PFV) protease-reverse transcriptase fusion (PR-RT) reveals conformational plasticity: implications for function

In most cases, proteolytic processing of the retroviral Pol portion of the Gag-Pol polyprotein precursor produces protease (PR), reverse transcriptase (RT), and integrase (IN). However, foamy viruses (FVs), express Pol separately from Gag and, when Pol is processed, only the IN domain is released. Here, we report a 2.9 [A] resolution crystal structure of the mature PR-RT from prototype FV (PFV) that carries out both proteolytic processing and reverse transcription. PFV PR-RT is monomeric and the architecture of PFV PR is similar to one of the subunits of HIV-1 PR, which is a dimer. There is a C-terminal extension of PFV PR (101-145) that consists of two helices which are adjacent to the base of the RT palm subdomain, and anchors PR to RT. The polymerase domain of PFV RT consists of fingers, palm, thumb, and connection subdomains whose spatial arrangements are similar to the p51 subunit of HIV-1 RT. The RNase H and polymerase domains of PFV RT are connected by flexible linkers. Significant spatial and conformational (sub)domain rearrangements are therefore required for nucleic acid binding. The structure of PFV PR-RT provides insights into the conformational maturation of retroviral Pol polyproteins. IMPORTANCERetroviruses such as HIV and other human and animal pathogens have evolved to maximize the protein-coding capacity of their genomes. Retroviruses synthesize large polyprotein precursors that are subsequently cleaved to produce mature functional enzymes and structural proteins from the same mRNA template. These polyproteins play an important role in the viral life cycle. We report the monomeric structure of the prototype foamy virus protease-reverse transcriptase fusion (PR-RT) which serves as both a protease and reverse transcriptase. The monomeric PR domain is folded in a similar way as a single subunit of dimeric HIV-1 PR. PR is anchored close to the fingers subdomain of the RT by a long C-terminal extension (CTE) that folds into two helices that pack against the palm subdomain of the RT. The RT is folded similarly to the p51 subunit of HIV-1 RT with the RNase H subdomain packed against the thumb and opposite the connection and palm subdomains. This structure offers insight into the structural arrangement of the domains and subdomains of immature retroviral polyproteins and provides support for the concept of developing drugs that target interfaces between immature enzymes that are present only in retroviral polyprotein precursors.

biophysics↗

Unique features of stimulus-based probabilistic reversal learning

Reversal learning paradigms are widely-used assays of behavioral flexibility with their probabilistic versions being more amenable to studying integration of reward outcomes over time. Prior research suggests differences between initial and reversal learning, including higher learning rates, a greater need for inhibitory control, and more perseveration after reversals. However, it is not well-understood what aspects of stimulus-based reversal learning are unique to reversals, and whether and how observed differences depend on reward probability. Here, we used a visual probabilistic discrimination and reversal learning paradigm where male and female rats selected between a pair of stimuli associated with different reward probabilities. We compared accuracy, rewards collected, omissions, latencies, win-stay/lose-shift strategies, and indices of perseveration across two different reward probability schedules. We found that discrimination and reversal learning are behaviorally more unique than similar: latencies to select the better option, win-stay strategies, and perseveration were of a different pattern in reversal learning compared to discrimination learning. Additionally, fit of choice behavior using reinforcement learning models revealed a lower sensitivity to the difference in subjective reward values (greater exploration) and higher learning rates for the reversal phase. Interestingly, a consistent reward probability group difference emerged with a richer environment associated with longer reward collection latencies than a leaner environment. We also replicated previous reports on sex differences in reversal learning. Future studies should systematically compare the neural correlates of fine-grained behavioral measures to reveal possible dissociations in how the circuitry is recruited in each phase.

animal behavior and cognition↗

Sex-dependent effects of chronic intermittent voluntary alcohol consumption on attentional, not motivational, measures during probabilistic learning and reversal

BackgroundForced alcohol (ethanol, EtOH) exposure has been shown to cause significant impairments on reversal learning, a widely-used assay of cognitive flexibility, specifically on fully-predictive, deterministic versions of this task. However, previous studies have not adequately considered voluntary EtOH consumption and sex effects on probabilistic reversal learning. The present study aimed to fill this gap in the literature. MethodsMale and female Long-Evans rats underwent either 10 weeks of voluntary intermittent 20% EtOH access or water only (H2O) access. Rats were then pretrained to initiate trials and learn stimulus-reward associations via touchscreen response, and subsequently required to select between two visual stimuli, rewarded with probability 0.70 or 0.30. In the final phase, reinforcement contingencies were reversed. ResultsWe found significant sex differences on several EtOH-drinking variables, with females reaching a higher maximum EtOH consumption, exhibiting more high-drinking days, and escalating their EtOH at a quicker rate compared to males. During early abstinence, EtOH drinkers made more initiation omissions and were slower to initiate trials than H2O drinking controls, particularly during pretraining. EtOH drinking females were most affected. A similar pattern in trial initiations was also observed in discrimination, but not in reversal learning. EtOH drinking rats were unaffected in their reward collection and stimulus response times, indicating intact motivation and motor responding. Although there were sex differences in discrimination and reversal phases, performance improved over time. We also observed sex-independent drinking group differences in win-stay and lose-shift strategies specific to the reversal phase. ConclusionsFemales exhibit increased vulnerability to EtOH effects in early learning: there were sex-dependent EtOH effects on attentional measures during pretraining and discrimination phases. We also found sexindependent EtOH effects on exploration strategies during reversal. Future studies should aim to uncover the neural mechanisms for changes in attention and exploration in both acute and prolonged EtOH withdrawal.

pharmacology and toxicology↗

Cryo-EM structures reveal transcription initiation steps by yeast mitochondrial RNA polymerase

Cryo-EM structures of transcription pre-initiation complex (PIC) and initiation complex (IC) of yeast mitochondrial RNA polymerase show fully resolved transcription bubbles and explain promoter melting, template alignment, DNA scrunching, transition into elongation, and abortive synthesis. Promoter melting initiates in PIC with MTF1 trapping the -4 to -2 non-template (NT) bases in its NT-groove. Transition to IC is marked by a large-scale movement that aligns the template with RNA at the active site. RNA synthesis scrunches the NT strand into an NT-loop, which interacts with centrally positioned MTF1 C-tail. Steric clashes of the C-tail with RNA:DNA and NT-loop, and dynamic scrunching-unscrunching of DNA explain abortive synthesis and transition into elongation. Capturing the catalytically active IC-state with UTPS poised for incorporation enables modeling toxicity of antiviral nucleosides/nucleotides.

biophysics↗

In silico chemical profiling and identification of neuromodulators from Curcuma amada targeting Acetylcholinesterase

Curcuma amada or Mango ginger, a member of the Zingiberaceae family, has been revealed as a beneficiary medicinal plant having diverse pharmacological activities against a wide range of diseases. Due to having neuromodulation properties of this plant, the present study characterized the secondary metabolites of Curcuma amada for their drug-likeness properties, identified potent hits by targeting Acetylcholinesterase (AChE) and revealed neuromodulatory potentiality by network pharmacology approaches. Here in silico ADMET analysis was performed for chemical profiling, and molecular docking and molecular dynamics simulations were used to hit selection and binding characterizations. Accordingly, ADMET prediction showed that around 87.59% of compounds processed drug-likeness activity, where four compounds have been screened out by molecular docking. Guided from induced-fit docking, molecular dynamics simulations revealed phytosterol and curcumin derivatives as the most favorable AChE inhibitors with the highest binding energy, as resulted from MM-PBSA analysis. Furthermore, all of the four hits were appeared to modulate several signaling molecules and intrinsic cellular pathways in network pharmacology analysis, which are associated with neuronal growth survival, inflammation, and immune response, supporting their capacity to revert the condition of neuro-pathobiology. Together, the present in silico based characterization and system pharmacology based findings demonstrate Curcuma amada, as a great source of neuromodulating compounds, which brings about new development for complementary and alternative medicine for the prevention and treatment of neurodegenerative disorders.

bioinformatics↗

Visual processing and attention rather than face and emotion processing play a distinct role in ASD: an EEG study

Autism Spectrum Disorder results in deficit in social interaction, non-verbal communication and social reciprocity. Cognitive tasks pertaining to emotion processing are often preferred to distinguish the ASD children from the typically developing ones. We analysed the role of face and emotion processing in ASD and explored the feasibility of using EEG as a neural marker for detecting ASD. Subjects performed a visual perceptual task with face and nonface stimuli. Successful ASD detection was possible as early as 50 ms. post stimulus onset. Alpha and Beta oscillations seem to best identify autistic individuals. Multivariate pattern analysis and source localization studies points to the role of early visual processing and attention rather than emotion and face processing in detecting autism.

animal behavior and cognition↗

Neural Mediators of Altered Perceptual Choice and Confidence Using Social Information

Understanding how individuals utilize social information while making perceptual decisions and how it affects their decision confidence is crucial in a society. Till date, very little is known about perceptual decision making in humans under the influence of social cues and the associated neural mediators. The present study provides empirical evidence of how individuals get manipulated by social cues while performing a face/car identification task. Subjects were significantly influenced by what they perceived as decisions of other subjects while the cues in reality were manipulated independently from the stimulus. Subjects in general tend to increase their decision confidence when their individual decision and social cues coincide, while their confidence decreases when cues conflict with their individual judgments often leading to reversal of decision. Using a novel statistical model, it was possible to rank subjects based on their propensity to be influenced by social cues. This was subsequently corroborated by analysis of their neural data. Neural time series analysis revealed no significant difference in decision making using social cues in the early stages unlike neural expectation studies with predictive cues. Multivariate pattern analysis of neural data alludes to a potential role of frontal cortex in the later stages of visual processing which appeared to code the effect of social cues on perceptual decision making. Specifically medial frontal cortex seems to play a role in facilitating perceptual decision preceded by conflicting cues.

neuroscience↗

Rat bone marrow derived mesenchymal stem cells differentiate to germ cell like cells

Summary StatementThe in vitro differentiation of rMSCs provides an excellent model for studying cell commitment and their potential in stem cell technology. We have demonstrated that rat bone marrow derived MSCs are able to differentiate into germ-line cells in vitro which has an enormous scope in the advancement of fertility research. In future, this technique can be utilized in different domestic animal species for propagation of elite germ plasm.\n\nAbstractGerm cells undergo distinctive male or female pathways to produce spermatozoa or oocyte respectively essential for sexual reproduction. Mesenchymal stem cells (MSCs) have the capacity of trans-differentiation to form the multiple lineages of cells of mesoderm, endoderm, and ectoderm origin. Herein, MSCs were isolated from rat bone marrow and characterized by their morphological features, expression of surface markers by immunophenotyping and molecular biology tools as well as self renewal and differentiation capability. Thereafter, by inducing these cells with retinoic acid we could able to show that bone marrow derived MSCs are able to trans-differentiate into male germ cell-like cells which were further characterized by the expressions of germ cell specific markers. This in vitro study for the generation of germ-like cells suggests that bone marrow MSCs can be a potential source of germ cells that could be a sustainable source of sperm / oocyte production for potential therapeutic applications in future. Moreover, this technique can be applied in different domestic animal species for propagation of elite germ plasm.

cell biology↗

Structural basis of ECF-sigma-factor-dependent transcription initiation.

Extracytoplasmic (ECF) {sigma} factors, the largest class of alternative {sigma} factors, are related to primary {sigma} factors, but have simpler structures, comprising only two of the six conserved functional modules present in primary {sigma} factors: region 2 ({sigma}R2) and region 4 ({sigma}R4). Here, we report crystal structures of transcription initiation complexes containing Mycobacterium tuberculosis RNA polymerase (RNAP), M. tuberculosis ECF {sigma} factor {sigma}L, and promoter DNA. The structures show that {sigma}R2 and {sigma}R4 of the ECF {sigma} factor occupy the same sites on RNAP as in primary {sigma} factors, show that the connector between {sigma}R2 and {sigma}R4 of the ECF {sigma} factor--although unrelated in sequence--follows the same path through RNAP as in primary {sigma} factors, and show that the ECF {sigma} factor uses the same strategy to bind and unwind promoter DNA as primary {sigma} factors. The results define protein-protein and protein-DNA interactions involved in ECF-{sigma}-factor-dependent transcription initiation.

molecular biology↗

Structural basis of transcription inhibition by fidaxomicin (lipiarmycin A3)

Fidaxomicin is an antibacterial drug in clinical use in treatment of Clostridium difficile diarrhea1-2. The active pharmaceutical ingredient of fidaxomicin, lipiarmycin A3 (Lpm)1-4, is a macrocyclic antibiotic with bactericidal activity against Gram-positive bacteria and efflux-deficient strains of Gram-negative bacteria1-2, 5. Lpm functions by inhibiting bacterial RNA polymerase (RNAP)6-8. Lpm exhibits no cross-resistance with the classic RNAP inhibitor rifampin (Rif)7, 9 and inhibits transcription initiation at an earlier step than Rif8-11, suggesting that the binding site and mechanism of Lpm differ from those of Rif. Efforts spanning a decade to obtain a crystal structure of RNAP in complex with Lpm have been unsuccessful. Here, we report a cryo-EM12-13 structure of Mycobacterium tuberculosis RNAP holoenzyme in complex with Lpm at 3.5 [A] resolution. The structure shows that Lpm binds at the base of the RNAP \"clamp,\" interacting with the RNAP switch region and the RNAP RNA exit channel. The binding site on RNAP for Lpm does not overlap the binding sites for other RNAP inhibitors, accounting for the absence of cross-resistance of Lpm with other RNAP inhibitors. The structure exhibits an open conformation of the RNAP clamp, with the RNAP clamp swung outward by ~17{degrees} relative to its position in catalytically competent RNAP-promoter transcription initiation complexes, suggesting that Lpm traps an open-clamp conformational state. Single-molecule fluorescence resonance energy transfer14 experiments confirm that Lpm traps an open-clamp conformational state and define effects of Lpm on clamp opening and closing dynamics. We propose that Lpm inhibits transcription initiation by trapping an open-clamp conformational state, thereby preventing simultaneous engagement of transcription initiation factor {sigma} regions 2 and 4 with promoter -10 and -35 elements. The results provide information essential to understanding the mode of action of Lpm, account for structure-activity relationships of known Lpm analogs, and suggest modifications to Lpm that could yield new, improved Lpm analogs.

molecular biology↗

Revealing unidentified heterogeneity in different epithelial cancers using heterocellular subtype classification

Cancers are currently diagnosed, categorised, and treated based on their tissue of origin. However, how different cellular compartments of tissues (e.g., epithelial, immune and stem cells) are similar across cancer types is unknown. Here we used colorectal cancer subtypes and their signatures representing different colonic crypt cell types as surrogates to classify different epithelial cancers into five heterotypic cellular (heterocellular) subtypes. The stem-like and inflammatory heterocellular subtypes are ubiquitous across epithelial cancers so capture intrinsic, tissue-independent properties. Conversely, well-differentiated/specialized goblet-like/enterocyte heterocellular subtypes differ across cancer types due to their colorectum-specific genes. The transit-amplifying heterocellular subtype shows a dynamic range of cellular differentiation with shared common pathways (Wnt, FGFR) in certain cancer types. Importantly, this approach revealed previously unrecognised heterogeneity in pancreatic, breast, microsatellite-instability enriched and KRAS mutation-dependent cancers. Immune cell-type differences are common and useful for patient stratification for immunotherapy. This unique approach identifies cell type-dependent but tissue-independent heterogeneity in different cancers for precision medicine.

bioinformatics↗