Structural basis for the mechanism and substrate specificity of glycocyamine kinase, a phosphagen kinase family member

The crystal structure determination of recombinant GK[alpha][beta] and GK[beta][beta] from the marine worm Namalycastis sp. with a transition state analogue, [Mg.sup.2+]-ADP-N[O.sup.3-]-glycocyamine is described. The active site environments of the glycocyamine kinase (GK), homodimeric creatine kinase (CK), and monomeric arginine kinase (AK) at the bound states provide insight into the structural determinants of substrate specificity and the coupling between the structural asymmetry and negative cooperativity proposed for CK which is not supported in the case of GK.