K. Veluraja

Database Analysis of O-Glycosylation Sites in Proteins

Statistical analysis was carried out to study the sequential aspects of amino acids around the O-glycosylated Ser/Thr. 992 sequences containing O-glycosylated Ser/Thr were selected from the O-GLYCBASE database of O-glycosylated proteins. The frequency of occurrence of amino acid residues around the glycosylated Ser/Thr revealed that there is an increased number of proline residues around the O-glycosylation sites in comparison with the nonglycosylated serine and threonine residues. The deviation parameter calculated as a measure of preferential and nonpreferential occurrence of amino acid residues around the glycosylation site shows that Pro has the maximum preference around the O-glycosylation site. Pro at +3 and/or -1 positions strongly favors glycosylation irrespective of single and multiple glycosylation sites. In addition, serine and threonine are preferred around the multiple glycosylation sites due to the effect of clusters of closely spaced glycosylated Ser/Thr. The preference of amino acids around the sites of mucin-type glycosylation is found likely to be similar to that of the O-glycosylation sites when taken together, but the acidic amino acids are more preferred around Ser/Thr in mucin-type glycosylation when compared totally. Aromatic amino acids hinder O-glycosylation in contrast to N-glycosylation. Cysteine and amino acids with bulky side chains inhibit O-glycosylation. The preference of certain potential sequence motifs of glycosylation has been discussed.

Monosialogangliosides and Their Interaction with Cholera Toxin—Investigation by Molecular Modeling and Molecular Mechanics

Abstract Molecular mechanics and molecular dynamics studies are performed to investigate the conformational preference of cell surface monosialogangliosides (GM3, GM2 and GM1) in aqueous environment. Water mediated hydrogen bonding network plays a significant role in the structural stabilization of GM3, GM2 and GM1. The spatial flexibility of NeuNAc of gangliosides at the binding site of cholera toxin reveals a limited allowed eulerian space of 2.4% with a much less allowed eulerian space (1.4%) for external galactose of GM1. The molecular mechanics of monosialoganglioside-cholera toxin complex reveals that cholera toxin can accommodate the monosialogangliosides in three different modes. Direct and water mediated hydrogen bonding interactions stabilize these binding modes and play an essential role in defining the order of specificity for different monosialogangliosides towards cholera toxin. This study identifies the NeuNAc binding site as a site for design of inhibitors that can restrict the pathogenic activity of cholera toxin.

Theoretical Investigation on the Binding Specificity of Sialyldisaccharides with Hemagglutinins of Influenza A Virus by Molecular Dynamics Simulations

Background: Recognition of terminal sialyldisaccharides by influenza A hemagglutinin initiates the infection process of influenza. Results: MD simulations on sialyldisaccharide-hemagglutinin (H1, H3, H5, and H9) complexes reveal the molecular basis of specific recognition. Conclusion: The order of the binding specificity of Neu5Acα(2–3)Gal and Neu5Acα(2–6)Gal is H3 > H5 > H9 > H1 and H1 > H3 > H5 > H9, respectively. Significance: The insights from this study will help in designing carbohydrate-based therapeutics against influenza viral infections. Recognition of cell-surface sialyldisaccharides by influenza A hemagglutinin (HA) triggers the infection process of influenza. The changes in glycosidic torsional linkage and the receptor conformations may alter the binding specificity of HAs to the sialylglycans. In this study, 10-ns molecular dynamics simulations were carried out to examine the structural and dynamic behavior of the HAs bound with sialyldisaccharides Neu5Acα(2–3)Gal (N23G) and Neu5Acα(2–6)Gal (N26G). The analysis of the glycosidic torsional angles and the pair interaction energy between the receptor and the interacting residues of the binding site reveal that N23G has two binding modes for H1 and H5 and a single binding mode for H3 and H9. For N26G, H1 and H3 has two binding modes, and H5 and H9 has a single binding mode. The direct and water-mediated hydrogen bonding interactions between the receptors and HAs play dominant roles in the structural stabilization of the complexes. It is concluded from pair interaction energy and Molecular Mechanic-Poisson-Boltzmann Surface Area calculations that N26G is a better receptor for H1 when compared with N23G. N23G is a better receptor for H5 when compared with N26G. However, H3 and H9 can recognize N23G and N26G in equal binding specificity due to the marginal energy difference (≈2.5 kcal/mol). The order of binding specificity of N23G is H3 > H5 > H9 > H1 and N26G is H1 > H3 > H5 > H9, respectively. The proposed conformational models will be helpful in designing inhibitors for influenza virus.

Conformations of Higher Gangliosides and Their Binding with Cholera Toxin—Investigation by Molecular Modeling, Molecular Mechanics, and Molecular Dynamics

Abstract Molecular mechanics and molecular dynamics studies are performed to investigate the conformational preference of cell surface higher gangliosides (GT1A and GT1B) and their interaction with Cholera Toxin. The water mediated hydrogen bonding network exists between sugar residues in gangliosides. An integrated molecular modeling, molecular mechanics, and molecular dynamics calculation of cholera toxin complexed with GT1A and GT1B reveal that, the active site of cholera toxin can accommodate these higher gangliosides. Direct and water mediated hydrogen bonding interactions stabilize these binding modes and play an essential role in defining the order of specificity for different higher ganglioside towards cholera toxin. This study identifies that the binding site of cholera toxin is shallow and can accommodate a maximum of two NeuNAc residues. The NeuNAc binding site of cholera toxin may be crucial for the design of inhibitors that can prevent the infection of cholera.

Preparation, properties and application of tamarind seed gum reinforced banana fibre composite materials

Technology has been developed to prepare a biodegradable and environmental friendly composite material from tamarind seed gum and banana fibre. Tamarind seed gum is prepared from the endosperm of roasted seeds of the tamarind tree. The different temperature condition maintained for roasting the seeds are 130, 160, and 180°C. Banana fibres are extracted from different varieties of banana trees, which are used for the preparation of composite material. The tensile strength of the composite material is measured and shows dependency on the variety of banana fibre used in the preparation and also the roasting temperature condition of the tamarind seed. Tamarind seed gum (the seed roasted at the temperature condition of 130°C) and Red banana fibre composite shows the highest tensile strength of 3.97 MPa and Poovan fibre composites shows the lowest tensile strength of 1.90 MPa. The composite material of other varieties shows tensile strength in between these two values. The percentage of moisture absorption of the composite material has a direct correlation to the tensile strength. In addition, investigation on fire retardant test of tamarind seed gum — banana fibre composite material revealed that untreated and varnish coated banana fibre composite material has good fire retardant characteristics. This is an important feature to promote the use of this composite material as a false roofing material instead of thermocole.

3DSDSCAR--a three dimensional structural database for sialic acid-containing carbohydrates through molecular dynamics simulation.

The inherent flexibility and lack of strong intramolecular interactions of oligosaccharides demand the use of theoretical methods for their structural elucidation. In spite of the developments of theoretical methods, not much research on glycoinformatics is done so far when compared to bioinformatics research on proteins and nucleic acids. We have developed three dimensional structural database for a sialic acid-containing carbohydrates (3DSDSCAR). This is an open-access database that provides 3D structural models of a given sialic acid-containing carbohydrate. At present, 3DSDSCAR contains 60 conformational models, belonging to 14 different sialic acid-containing carbohydrates, deduced through 10 ns molecular dynamics (MD) simulations. The database is available at the URL: http://www.3dsdscar.org.

Disialogangliosides and their interaction with cholera toxin: Investigation by molecular modeling, molecular mechanics and molecular dynamics

Abstract Molecular mechanics and molecular dynamics studies are performed to investigate the conformational preference of cell surface disialogangliosides (GD1A, GD1B and GD3) in aqueous environment. The molecular mechanics calculation reveals that water mediated hydrogen bonding network plays a significant role in the structural stabilization of GD1A, GD1B and GD3. These water mediated hydrogen bonds not only exist between neighboring residues but also exist between residues that are separated by 2 to 3 residues in between. The conformational energy difference between different conformational states of gangliosides correlates very well with the number of water mediated and direct hydrogen bonds. The spatial flexibility of NeuNAc of gangliosides at the binding site of cholera toxin is worked out. The NeuNAc has a limited allowed eulerian space at the binding site of Cholera Toxin (2.4%). The molecular modeling, molecular mechanics and molecular dynamics of disialo- ganglioside-cholera toxin complex reveal that cholera toxin can accommodate the disialo- ganglioside GD1A in three different modes. A single mode of binding is permissible for GD1B and GD3. Direct and water mediated hydrogen bonding interactions stabilizes these binding modes and play an essential role in defining the order of specificity for different disialogangliosides towards cholera toxin. This study not only provides models for the disialoganglioside-cholera toxin complexes but also identifies the NeuNAc binding site as a site for design of inhibitors that can restrict the pathogenic activity of cholera toxin.

Molecular Modeling of Sialyloligosaccharide Fragments into the Active site of Influenza Virus N9 Neuraminidase

Abstract Molecular modeling studies have been carried out to investigate the interactions between substrate sialyloligosaccharide (SOS) fragments bearing different glycosidic linkages and influenza virus N9 neuraminidase, a surface glycoprotein of influenza virus subtype N9. The studies revealed that the allowed orientation for sialic acid (SA) is less than 1% in the Eulerian space at the active site. The active site of this enzyme has enough space to accommodate various SOS fragments, NeuNAcα(2–3)Gal, NeuNAcα (2–6)Gal, NeuNAcα (2–8)NeuNAc and NeuNAcα (2–9)NeuNAc, but on specific conformations. In the bound conformation, among these substrates there exists a conformational similarity leading to a structural similarity, which may be an essential requirement for the cleavage activity of the neuraminidases irrespective of the type of glycosidic linkage.

Identification and Analysis of Binding Site Residues in Proteincarbohydrate Complexes using Energy Based Approach

Protein-carbohydrate interactions play important roles in several biological processes in living organisms. Understanding the recognition mechanism of protein-carbohydrate complexes is a challenging task in molecular and computational biology. In this work, we have developed an energy based approach for identifying the binding sites and important residues for binding in protein-carbohydrate complexes. Our method identified 3.3% of residues as binding sites in protein- carbohydrate complexes whereas the binding site residues in protein-protein, protein-RNA and protein-DNA complexes are 10.8%, 7.6% and 8.7%, respectively. In all these complexes, binding site residues are accommodated in singleresidue segments so that the neighboring residues are not involved in binding. Binding propensity analysis indicates the dominance of Trp to interact with carbohydrates through aromatic-aromatic interactions. Further, the preference of residue pairs and tripeptides interacting with carbohydrates has been delineated. The information gained in the present study will be beneficial for understanding the recognition mechanism of protein-carbohydrate complexes and for predicting the binding sites in carbohydrate binding proteins.

Molecular Modelling and Molecular Dynamics studies of GD1A, GD1B and their complexes with BoNT/B--perspectives in interaction and specificity.

The conformational property for the oligosaccharide structure of GD1A and GD1B in aqueous environment is studied by 10 ns Molecular Dynamics simulation using all atom model. Based on the trajectory analysis four conformational models are proposed for GD1A and one for GD1B. Direct and water mediated hydrogen bonding interactions plays a prominent role in stabilizing these conformational structures. The Molecular Modelling and 10 ns MD simulation of Botulinum Neuro Toxin/B-GD1A and BoNT/B-GD1B complex revealed that this toxin can interact with GD1A in the single binding mode and with GD1B in two binding modes. Least mobility is seen for GD1A in the binding pocket of BoNT/B. The GTSM comparison, pair interaction energy calculation, total energy calculation, MM/PBSA binding free energy calculation and RMSD predicts that GD1A is a better receptor for BoNT/B compared to GD1B. The internal NeuNAc1 tends to form more than 70% of hydrogen bonds with BoNT/B both in GD1A and GD1B, hence specifying this particular site as a crucial space for the therapeutic design that can restrict the pathogenic activity of BoNT/B.