The Role of the C-terminus in Bacillus subtilis Inorganic Pyrophosphatase Activity

Abstract

Inorganic pyrophosphatases hydrolyse inorganic pyrophosphate ensuring that the pool of phosphate is continuously available in a cell for subsequent metabolic reactions. Bacillus subtilis PPase is the first member of the Family II of PPases, unique not only in terms of physical/biochemical characteristics, but also enzyme primary structure. Prompted by the plausible existence of two distinct evolutionary paths for development of this universal function in the cell and, consequently, distinct active sites, a research into the role of a signature sequence near the C-terminus of B. subtilis enzyme was commenced. Two truncated variants and a series of site specific mutants were produced and the effect of the mutations on enzyme activity, stability and multimerization was analysed. Overall, there is no evidence for the C-terminus having a role in multimerization. However, both its conserved and non-conserved regions are absolutely vital for full enzyme activity. The signature sequence is found to be required for both the composition and correct conformation of the active site. Substrate specificity studies suggest the C-terminal domain is able to adopt a conformation permitting the binding of a larger substrate molecule. The work provides important insights into the nature of activity of Family II PPases that could facilitate design of drugs effective against a significant number of pathogenic microorganisms depending upon these enzymes for macromolecular syntheses.