Cooperativity in catalysis by canonical family II pyrophosphatases

Abstract

Bacterial family II pyrophosphatases (PPases) are homodimeric enzymes, with the active site located between two catalytic domains. Some family II PPases additionally contain regulatory cystathionine β-synthase (CBS) domains and exhibit positive kinetic cooperativity, which is lost upon CBS domain removal. We report here that CBS domain-deficient family II PPases of Bacillus subtilis and Streptococcus gordonii also exhibit positive kinetic cooperativity, manifested as an up to a five-fold difference in the Michaelis constants for two active sites. An Asn79Ser replacement in S. gordonii PPase preserved its dimeric structure but abolished cooperativity. The results of our study indicated that kinetic cooperativity is an inherent property of all family II PPase types, is not induced by CBS domains, and is sensitive to minor structural changes. These findings may have inferences for other CBS-proteins, which include important enzymes and membrane transporters associated with hereditary diseases.

Keywords: CBS domain; Cooperativity; Enzyme kinetics; Inorganic pyrophosphatase; Metalloenzyme.