The PPP-family protein phosphatases PrpA and PrpB of Salmonella entetica serovar typhimurium possess distinct biochemical properties

Salmonella enterica serovar Typhimurium requires Mn2+, but only a few Mn2+- dependent enzymes have been identified from bacteria. To characterize Mn2+- dependent enzymes from serovar Typhimurium, two putative PPP-family protein phosphatase genes were cloned from serovar Typhimurium and named prpA and prpB. Their DNA-derived amino acid sequences showed 61% identity to the cor responding Escherichia coli proteins and 41% identity to each other. Each p hosphatase was expressed in E. coli and purified to near electrophoretic ho mogeneity. Both PrpA and PrpB absolutely required a divalent metal for acti vity. As with other phosphatases of this class, Mn2+ had the highest affini ty and stimulated the greatest activity. The apparent K-a of PrpA for Mn2of 65 muM was comparable to that for other bacterial phosphatases, but PrpB had a much higher affinity for Mn2+ (1.3 muM). The pH optima were pH 6.5 f or PrpA and pH 8 for PrpB, while the optimal temperatures were 45 to 55 deg reesC for PrpA and 30 to 37 degreesC for PrpB. Each phosphatase could hydro lyze phosphorylated serine, threonine, or tyrosine residues, but their rela tive specific activities varied with the specific substrate tested. These d ifferences suggest that each phosphatase is used by serovar Typhimurium und er different growth or environmental conditions such as temperature or acid ity.