[
Parasitology,
2014]
Guanylate kinase, a nucleoside monophosphate kinase of Brugia malayi which is involved in reversible transfer of phosphate groups 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 the 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 and 38 m, 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 with human GK and showed ternary complex (BmGK-GMP-ATP) formation with sequential substrate binding. The secondary structure of BmGK consisted of 45% -helices, 18% -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 compared with human GK can provide the way for design of parasite-specific inhibitors.
[
Neuron,
1999]
Postsynaptic density 95 (PSD-95/SAP-90) is a membrane associated guanylate kinase (GK) PDZ protein that scaffolds glutamate receptors and associated signaling networks at excitatory synapses. Affinity chromatography identifies cypin as a major PSD-95-binding protein in brain extracts. Cypin is homologous to a family of hydrolytic bacterial enzymes and shares some similarity with collapsin response mediator protein (CRMP), a cytoplasmic mediator of semaphorin III signalling. Cypin is discretely expressed in neurons and is polarized to basal membranes in intestinal epithelial cells. Overexpression of cypin in hippocampal neurons specifically perturbs postsynaptic trafficking of PSD-95 and SAP-102, an effect not produced by overexpression of other PDZ ligands. In fact, PSD-95 can induce postsynaptic clustering of an otherwise diffusely localized K+ channel, Kv1.4. By regulating postsynaptic protein sorting, cypin may influence synaptic development and plasticity.