Research synopsis

Some of the early work carried out was on evolutionary relationship of viruses and structural comparison of proteins. Subsequently, the three-dimensional structures of two isometric ss-RNA plant viruses, sesbania mosaic virus and physalis mottle virus were determined using single crystal X-ray diffraction techniques. Their mode of assembly was investigated using structural and biophysical methods. These studies were extended to a number of site specific and deletion mutants of sesbania mosaic virus and physalis mottle virus. It was found that several of the mutants assemble in to virus like particles when expressed in E. coli. The structures of several deletion and site specific mutants were determined. The structures determined include particles with T=3 as well as T=1 icosahedral symmetry. The smaller T=1 particles are formed by N-terminal deletion mutants of sesbania mosaic virus. It was also possible to disrupt the assembly of sesbania mosaic virus by a suitable site specific mutation. The structure of a dimeric unit of sesbania mosaic virus coat protein obtained by disrupting the assembly was elucidated. In collaboration with P. Balaram and Hema Balaram, the three dimensional structures of three proteins from the malarial parasite, Plasmodium falciparum, triosephosphate isomerase, adenylosuccinate synthase and hypoxanthine guanine phosphoribosyl transferase and structures of several of their ligand complexes were determined. The structures of several enzymes involved in propionate and propanediol metabolism in Salmonella typhimurium have been structurally and biochemically elucidated. The enzymes studied include methylisocitrate lyase, methylcitrate synthase, acetate kinase, propionate kinase and threonine deaminase. Several ligand complexes of these enzymes have been structurally and biochemically investigated with the view of elucidating enzyme mechanisms. The structure and function of the pyridoxal phosphate dependent enzyme serinehydroxymethyl transferase from Bacillus stearothermophilus has been extensively investigated. Structures of the native and ligand complexes of pyridoxal phosphate dependent enzymes actetylornithine aminotransferase, D-serine deaminase, D-cysteine desulfhydrase, arginine decarboxylase from Salmonella typhimurium have been determined and related to their function. Structures of another pyridoxal dependent enzyme diaminopropionate lyase from E. coli and its complexes with ligands have been determined. Structures a few other enzymes, adenylosuccinate synthase, propanol dehydrogenase and a mutarotase from Salmonella typhimurium have been elucidated. Structures of several proteins such as SurE, YnaF, Yda that are essential for the survival of Salmonella typhimurium under environmental stress have been determined. SurE has been used as a model protein to investigate the significance of domain swapping interactions in protein symmetry and function. The most recent work carried out in collaboration with Rik Wierenga is on the structure and function of SCP2-like thiolases of prokaryotes.

Collaborators