The hppA gene of Helicobacter pylori encodes the class C acid phosphatase precursor.

Screening of the Helicobacter pylori genomic library with sera from infected humans and from immunized rabbits resulted in identification of the 25 kDa protein cell envelope (HppA) which exhibits acid phosphatase activity. Enzyme activity was demonstrated by specific enzymatic assays with whole-cell protein preparations of H. pylori strain N6 and from Escherichia coli carrying the hppA gene (pUWM192). HppA showed optimum activity at pH 5.6 and was resistant to inhibition by EDTA. Bioinformatics analysis and site-directed mutagenesis of two putative active site residues (D73 and D192) provide further insight into the sequence-structure-function relationships of HppA as a member of the DDDD phosphohydrolase superfamily.