Molecular evolution, binding site interpretation and functional divergence of aspartate semialdehyde dehydrogenase.

Aspartate Semialdehyde Dehydrogenase (ASDH) is an important enzyme essential for the viability of pathogenic microorganisms. ASDH is mainly involved in amino acid and cell wall biosynthesis of microorganisms, hence it is considered to be a promising target for drug design. This enzyme depicts similar mechanistic function in all microorganisms; although, the kinetic efficiency of an enzyme differs according to their active site residual composition. Therefore, understanding the residual variation and kinetic efficiency of the enzyme would pave new insights in structure-based drug discovery and a novel drug molecule against ASDH. Here, ASDH from endosymbiont of is used as a prime enzyme to execute evolutionary studies. The phylogenetic analysis was opted to classify 400 sequences of ASDH enzymes based on their structure and electrostatic surfaces. Analysis resulted in 37 monophyletic clades of diverse pathogenic and non-pathogenic organisms. The representative structures of 37 ASDHs from different clades were further deciphered to structural homologues. These enzymes exhibited presence of more positively charged surfaces than negatively charged surfaces in the active site pocket which restrains evolutionary significance. Docking studies of NADP with 37 enzymes reveals that site-specific residual variation in the active site pocket modulates the binding affinity (ranges of -13 to -9 kcal/mol). Type-I and Type-II divergence studies show, no significant functional divergence among ASDH, but residual changes were found among the enzyme that modulates the biochemical characteristics and catalytic efficiency. The present study not only explores residual alteration and catalytic variability, it also aids in the design of species-specific inhibitors.Communicated by Ramaswamy H. Sarma.