The Stoichiometry of Binding of ATP and Its Derivatives to a Recombinant Selenophosphate Synthetase E197D Catalytically Inactive Mutant C17S

Selenophosphate synthetase (SPS) catalyses formation of the universal donor of selenium equivalents in a living cell. It performs the selenophosphate formation from ATP and selenide in ATP-dependent manner. We have checked a catalytically inactive mutant C17S of bacterial SPS from E.coli, E197D, for ATP hydrolysis and ATP-binding. The ratio obtained for ATP-binding is 9.52 nM ATP: 7.0 nmol enzyme, however, the fraction of the protein applied to the size-exclusive column TSK 2000 under reaction conditions was homogenious. It is likely under the ATP-binding conditions C17S mutant of SPS represents a monomer. A sequence alignment of bacterial mutant C17S from strain K12 with a human SEPHSI shows it exhibits of 31% homology. It is supposingly SPSI is a functional and structural analogue of C17S and has a similar biological activity.