Semanti Ghosh

Hypoglycosylation of dystroglycan due to T192M mutation: a molecular insight behind the fact.

Abnormal glycosylation of dystroglycan (DG), a transmembrane glycoprotein, results in a group of diseases known as dystroglycanopathy. A severe dystroglycanopathy known as the limb girdle disease MDDGC9 [OMIM: 613818] occurs as a result of hypoglycosylation of alpha subunit of DG. Reasons behind this has been traced back to a point mutation (T192M) in DG that leads to weakening of interactions of DG protein with laminin and subsequent loss of signal flow through the DG protein. In this work we have tried to analyze the molecular details of the interactions between DG and laminin1 in order to propose a mechanism about the onset of the disease MDDGC9. We have observed noticeable changes between the modeled structures of wild type and mutant DG proteins. We also have employed molecular docking techniques to study and compare the binding interactions between laminin1 and both the wild type and mutant DG proteins. The docking simulations have revealed that the mutant DG has weaker interactions with laminin1 as compared to the wild type DG. Till date there are no previous reports that deal with the elucidation of the interactions of DG with laminin1 from the molecular level. Our study is therefore the first of its kind which analyzes the differences in binding patterns of laminin1 with both the wild type and mutant DG proteins. Our work would therefore facilitate analysis of the molecular mechanism of the disease MDDGC9. Future work based on our results may be useful for the development of suitable drugs against this disease.

A structural perspective on the interactions of TRAF6 and Basigin during the onset of melanoma: A molecular dynamics simulation study

Metastatic melanoma is the most fatal type of skin cancer. The roles of matrix metalloproteinases (MMPs) have well been established in the onset of melanoma. Basigin (BSG) belongs to the immunoglobulin superfamily and is critical for induction of extracellular MMPs during the onset of various cancers including melanoma. Tumor necrosis factor receptor‐associated factor 6 (TRAF6) is an E3‐ligase that interacts with BSG and mediates its membrane localization, which leads to MMP expression in melanoma cells. This makes TRAF6 a potential therapeutic target in melanoma. We here conducted protein‐protein interaction studies on TRAF6 and BSG to get molecular level insights of the reactions. The structure of human BSG was constructed by protein threading. Molecular‐docking method was applied to develop the TRAF6‐BSG complex. The refined docked complex was further optimized by molecular dynamics simulations. Results from binding free energy, surface properties, and electrostatic interaction analysis indicate that Lys340 and Glu417 of TRAF6 play as the anchor residues in the protein interaction interface. The current study will be helpful in designing specific modulators of TRAF6 to control melanoma metastasis.

Intermolecular Interaction Study of Dissimilatory Sulfite Reductase (DsrAB) from Sulfur Oxidizing Proteobacteria Allchromatium vinosum

Dissimilatory Sulfite Reductase (dSiR) is the main redox enzyme system utilized in sulfur metabolism in both sulfur oxidizing and reducing prokaryotes. Anoxygenic phototrophic bacteria Allochromatium vinosum produces elemental sulfur during sulfur cycle which is ultimately oxidized sulfate by DSR operon. Allochromatium vinosum encodes dsrAB reverse dSiR that oxidizes thiosulfate or elemental sulfur. DsrAB is a α2β2 hetero-tetrameric complex. In our present study, we first reported the three dimensional structure of DsrAB protein complex from Allochromatium vinosum and we also predicted the protein-protein interactions between DsrA and DsrB proteins. DsrAB is a major redox enzyme complex required in both sulfur oxidation and reduction processes so this structure function relationship investigation will help in researches to predict the biochemical mechanism of sulfur-oxidation. The importance of the study lies in the fact that sulfur metabolism pathways are used in waste remediation and bio-hydrogen production. This is the most important aspect of our analysis.

Comparative analysis of the mechanisms of sulfur anion oxidation and reduction by dsr operon to maintain environmental sulfur balance

Sulfur metabolism is one of the oldest known redox geochemical cycles in our atmosphere. These redox processes utilize different sulfur anions and the reactions are performed by the gene products of dsr operon from phylogenetically diverse sets of microorganisms. The operon is involved in the maintenance of environmental sulfur balance. Interestingly, the dsr operon is found to be present in both sulfur anion oxidizing and reducing microorganisms and in both types of organisms DsrAB protein complex plays a vital role. Though there are various reports regarding the genetics of dsr operon there are practically no reports dealing with the structural aspects of sulfur metabolism by dsr operon. In our present study, we tried to compare the mechanisms of sulfur anion oxidation and reduction by Allochromatium vinosum and Desulfovibrio vulgaris respectively through DsrAB protein complex. We analyzed the modes of bindings of sulfur anions to the DsrAB protein complex and observed that for sulfur anion oxidizers, sulfide and thiosulfate are the best substrates whereas for reducers sulfate and sulfite have the best binding abilities. We analyzed the binding interaction pattern of the DsrA and DsrB proteins while forming the DsrAB protein complexes in Desulfovibrio vulgaris and Allochromatium vinosum. To our knowledge this is the first report that analyzes the differences in binding patterns of sulfur substrates with DsrAB protein from these two microorganisms. This study would therefore be essential to predict the biochemical mechanism of sulfur anion oxidation and reduction by these two microorganisms i.e., Desulfovibrio vulgaris (sulfur anion reducer) and Allochromatium vinosum (sulfur anion oxidizer). Our observations also highlight the mechanism of sulfur geochemical cycle which has important implications in future study of sulfur metabolism as it has a huge application in waste remediation and production of industrial bio-products viz. vitamins, bio-polyesters and bio-hydrogen.

Insight into the molecular mechanism of the sulfur oxidation process by reverse sulfite reductase (rSiR) from sulfur oxidizer Allochromatium vinosum

Sulfur metabolism is one of the oldest known biochemical processes. Chemotrophic or phototrophic proteobacteria, through the dissimilatory pathway, use sulfate, sulfide, sulfite, thiosulfate or elementary sulfur by either reductive or oxidative mechanisms. During anoxygenic photosynthesis, anaerobic sulfur oxidizer Allochromatium vinosum forms sulfur globules that are further oxidized by dsr operon. One of the key redox enzymes in reductive or oxidative sulfur metabolic pathways is the DsrAB protein complex. However, there are practically no reports to elucidate the molecular mechanism of the sulfur oxidation process by the DsrAB protein complex from sulfur oxidizer Allochromatium vinosum. In the present context, we tried to analyze the structural details of the DsrAB protein complex from sulfur oxidizer Allochromatium vinosum by molecular dynamics simulations. The molecular dynamics simulation results revealed the various types of molecular interactions between DsrA and DsrB proteins during the formation of DsrAB protein complex. We, for the first time, predicted the mode of binding interactions between the co-factor and DsrAB protein complex from Allochromatium vinosum. We also compared the binding interfaces of DsrAB from sulfur oxidizer Allochromatium vinosum and sulfate reducer Desulfovibrio vulgaris. This study is the first to provide a comparative aspect of binding modes of sulfur oxidizer Allochromatium vinosum and sulfate reducer Desulfovibrio vulgaris.

Alanine substitution mutations in the DNA binding region of a global staphylococcal virulence regulator affect its structure, function, and stability

SarA, a winged-helix DNA binding protein, is a global virulence regulator in Staphylococcus aureus. The putative DNA binding region of SarA is located between amino acid residues Leu 53 and Gln 97. Previous studies have demonstrated that residues at positions 84, 88, 89, and 90 are critical for its function. To precisely understand the roles of the DNA binding residues, we have investigated nine mutants of a recombinant SarA (rSarA) along with the rSarA mutants carrying mutations at the above four positions. Of the thirteen mutants, eleven mutants show weaker DNA binding activity in vitro compared to rSarA. As noted earlier, the DNA binding affinity of rSarA was maximally affected due to the mutation at position 84 or 90. Each of the functionally-defective mutants also possesses an altered structure and stability. Additionally, the mutations at positions 84 and 90 have severely affected the formation of hydrogen (H) bonds at the interface between SarA and the cognate DNA. The mutation at position 64 also has perturbed the generation of some interface H-bonds. Therefore, the disruption of H-bonds in the protein-DNA interface and the structural alteration in the protein may be responsible for the reduced DNA binding activity of the mutants.

Molecular Interactions, Structural Transitions and Alterations in SoxB Protein Due to SoxYZ Interaction from Two Distinct β-Proteobacteria: An In silico Approach Towards the Thiosulfate Oxidation and Recycling of SoxY Protein

Microbial oxidation–reduction reactions utilizing the environmental thiosulfate ions and mediated mainly by the sox operon are very much essential to maintain the sulfur balance in the environment. Majority of the previously documented wet laboratory studies show genetics behind the functionality of Sox proteins encoded by the sox operon. However, the molecular details of the involvements of the essential SoxB, SoxY and SoxZ proteins in the beta-proteobacteria have not yet been elucidated. In this work, an attempt was made to analyze the interaction profiles of the aforementioned SoxB, SoxY and SoxZ proteins to predict their roles in biological sulfur oxidation process. In order to establish the possible roles of these Sox proteins, we built the homology models of these proteins from the two different beta-proteobacteria Dechloromonas aromatica and Thiobacillus denitrificans. We then used molecular docking and simulation studies to further analyze the interaction profiles of these sox proteins. Our analyses revealed that SoxB protein from T. denitrificans exhibited steadier and stronger interactions with SoxYZ protein complex. On the other hand, SoxB protein from D. aromatica was found to exhibit a spontaneous interaction with greater ΔG values and therefore was well documented to exhibit a dual role. This is the first research article to discern the molecular level of interaction profiles of SoxB with SoxYZ protein complex in the beta-proteobacteria D. aromatica and T. denitrificans during the oxidations of thiosulfate. It would further prompt the future investigation into the mutational impact on the sequential interaction pattern in sox operon.

Structural study of the effects of mutations in proteins to identify the molecular basis of the loss of local structural fluidity leading to the onset of autoimmune diseases.

Protein-Protein Interactions (PPIs) are crucial in most of the biological processes and PPI dysfunctions are known to be associated with the onsets of various diseases. One of such diseases is the auto-immune disease. Auto-immune diseases are one among the less studied group of diseases with very high mortality rates. Thus, we tried to correlate the appearances of mutations with their probable biochemical basis of the molecular mechanisms leading to the onset of the disease phenotypes. We compared the effects of the Single Amino Acid Variants (SAVs) in the wild type and mutated proteins to identify any structural deformities that might lead to altered PPIs leading ultimately to disease onset. For this we used Relative Solvent Accessibility (RSA) as a spatial parameter to compare the structural perturbation in mutated and wild type proteins. We observed that the mutations were capable to increase intra-chain PPIs whereas inter-chain PPIs would remain mostly unaltered. This might lead to more intra-molecular friction causing a deleterious alteration of proteins normal function. A Lyapunov exponent analysis, using the altered RSA values due to polymorphic and disease causing mutations, revealed polymorphic mutations have a positive mean value for the Lyapunov exponent while disease causing mutations have a negative mean value. Thus, local spatial stochasticity has been lost due to disease causing mutations, indicating a loss of structural fluidity. The amino acid conversion plot also showed a clear tendency of altered surface patch residue conversion propensity than polymorphic conversions. So far, this is the first report that compares the effects of different kinds of mutations (disease and non-disease causing polymorphic mutations) in the onset of autoimmune diseases.

Analysis of the Structural Details of DsrO Protein from Allochromatium vinosum to Identify the Role of the Protein in the Redox Transport Process Through the dsr Operon

Sulfur oxidation is one of the oldest known redox processes in our environment mediated by phylogenetically diverse sets of microorganisms. The sulfur oxidation process is mediated mainly by dsr operon which is basically involved in the balancing and utilization of environmental sulfur compounds. DsrMKJOP complex from the dsr operon is the central player of this operon. DsrO is a periplasmic protein which binds FeS clusters responsible for electron transfer to DsrP protein from the dsr operon. DsrP protein is known to be involved in electron transfer to DsrM protein. DsrM protein would then donate the electrons to DsrK protein, the catalytic subunit of this complex. In the present work, we tried to analyze the role of DsrO protein of the dsr operon from the ecologically and industrially important organism Allochromatium vinosum. There are no previous reports that deal with the structural details of the DsrO protein. We predicted the structure of the DsrO protein obtained by homology modeling. The structure of the modeled protein was then docked with various sulfur anion ligands to understand the molecular mechanism of the transportation process of sulfur anion ligands by this DsrMKJOP complex. This study may therefore be considered as a first report of its kind that would therefore enlighten the pathway for analysis of the biochemical mechanism of sulfur oxidation reaction cycle by dsr operon.

Mutation study of DsrM from Allochromatium vinosum using the amino acid sequences.

Sulfur metabolism is one of the oldest known environmental processes. The operon involved in this process is called the dsr operon. The vital role of the operon is to maintain the environmental sulfur balance. The dsr operon of proteobacteria consists of 15 genes, viz. dsrABEFHCMKLJOPNRS. The proteins encoded by the dsr operon are essential for the transfer of sulfur globules from periplasm to cytosol and oxidation of the stored sulfur. In the present study we tried to analyze the probable molecular details of the DsrM proteins from a diverse set of microbial species using their sequence information. There are certain mutations in the sequences of the DsrM proteins from the different proteobacterial species. The effects of mutations in the sequences of DsrM proteins were predicted from the evolutionary point of view. This is so far the first report of its kind. Our study would therefore enable the researches to predict the hitherto unknown biochemistry of sulfur oxidation using the amino acid sequences of the DsrM proteins.