Structural-Functional Integrity of Hypothetical Proteins Identical to ADPribosylation Superfamily Upon Point Mutations

P.      Chellapandi

Abstract

In the present study, we have evaluated the impacts of point mutations on structural and functional evolution of hypothetical proteins identical to bacterial ADP-ribosylation superfamily members using bioinformatics approaches. A combined approach of molecular modelling and dynamics was employed to generate energetically stable structures from hypothetical protein sequences. Improper energy and structural constraints of the resulted homology models were stabilized by molecular dynamic simulation and hybrid Monte Carlo approaches. Since amino acid substitutions occurring in highly mutable functional sites, catalytic activity or substrate specificity would be expected to adjust without compromising their structural stability. In silico mutagenesis studies showed that protein structural stability has not been changed upon point mutations, but functional firmness has modified unusually from virulence to avirulence. Protein variants such as BTA3V10 (Gly⁴²¹→Val⁴²¹), BTA3V11 (Gly⁴²¹→Leu⁴²¹), BTA3V17 (Gly⁴²²→Phe⁴²²) and PTS15V1 (Cys²⁶→Met²⁶) and PTS15V2 (Cys²⁶→Thy²⁶) generated from this study showed to have a fast fold rate and stable energetic structures compared to wild type proteins. Overall, structures and functional integrity of the hypothetical proteins were identical to the members in bacterial ADP-ribosylation superfamily. A catalytic activity of ADP-ribosyltransferase existing in the hypothetical proteins would determine whether virulent state or avirulent state by deleterious mutations occurring in the subdynamic space of a conserved domain.

Keywords: ADP ribosylation, avirulent toxin, coevolution, functional evolution, point mutation, structural stability.

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