Abstract
The present work describes cloning, expression, purification, characterization, and mutation of
Plasmodium falciparum guanylate kinase (PlasmoDB ID PFI1420w). Amino-acid sequence alignment revealed important differences especially in K42-V51, Y73-A77, and F100-L110, which include residues important for kinase activity, and at helix 3, which is important for domain movements. The catalytic efficiency for dGMP was 22-fold lower than that for GMP, whose value is the lowest among known guanylate kinases. dGMP was found to a competitive inhibitor for GMP with
K
i
=
0.148
mM and a mixed-type inhibitor with regard to ATP with measured
K
i
=
0.4
mM. The specificity constant (
K
cat/
K
m) of the four examined mutants varied for natural substrate GMP/dGMP, indicating the involvement of different mechanisms in substrate recognition and subsequent loop-domain movement. These results show that
P. falciparum guanylate kinase is structurally and biochemically distinct from other guanylate kinases and could be a possible target in drug development.