Purification and Characterization of Guanylate kinase, a nucleoside monophosphate kinase of Brugia malayi

Abstract

Guanylate kinase, a nucleoside monophosphate kinase of Brugia malayi which is involved in reversible transfer of phosphate group from ATP to GMP, was cloned, expressed and characterized. The native molecular mass of BmGK was found to be 45 kDa as determined by Size Exclusion Chromatography and glutaraldehyde cross linking which revealed that protein is homodimer in nature. This is a unique characteristic among known eukaryotic GKs. GMP and ATP, served as the most effective phosphate acceptor and donor, respectively. Recombinant BmGK utilized both GMP and dGMP, as substrates showing Km. values of 30 µM and 38 µM, respectively. Free Mg+2 (un-complexed to ATP) and GTP play a regulatory role in catalysis of BmGK. The enzyme showed higher catalytic efficiency as compared to human enzyme and showed ternary complex (BmGK-GMP-ATP) formation with sequential substrate binding. The secondary structure of BmGK consisted of 45% α-helices, 18% β-sheets as revealed by CD analysis. Homology modelling and docking with GMP revealed conserved substrate binding residues with slight differences. Differences in kinetic properties and oligomerization of BmGK with human enzyme can provide the way for design of parasite specific inhibitors.