The IalA invasion gene of Bartonella bacilliformis encodes a (di)nucleoside polyphosphate hydrolase of the MutT motif family and has homologs in other invasive bacteria

The product of the ialA invasion gene of Bartonella bacilliformis has been expressed as a thioredoxin fusion protein. It is a (di)nucleoside polyphosphate hydrolase of the MutT motif protein family with strong sequence similarity to plant diadenosine tetraphosphate hydrolases. It hydrolyses nucleoside and dinucleoside polyphosphates with four or more phosphate groups, always producing an NTP as one product. Diadenosine tetraphosphate (Ap₄A) is the preferred substrate with a K(m) of 10 μM and a k(cat) of 3.0 s^-1. It is inhibited by Ca²⁺ and F^- (K(i) = 30 μM). Hydrolysis of Ap₄A in H₂¹⁸O yielded [¹⁸O]AMP as the only labelled product. In terms of sequence, reaction mechanism and properties, IalA is very similar to eukaryotic Ap₄A hydrolases and unlike previously described bacterial Ap₄A hydrolases. Homologs are present in the genomes of other invasive pathogens. They may function to reduce stress-induced dinucleotide levels during invasion and so enhance pathogen survival.