A free terminal carboxylate group is required for PhrA pentapeptide inhibition of RapA phosphatase

In the Bacillus subtilis phosphorelay signal transduction system for sporul ation initiation, signals competing with the differentiation process are in terpreted by aspartyl-phosphate phosphatases that specifically dephosphoryl ate the Spo0F or Spo0A response regulators. The RapA phosphatase. is regula ted by the PhrA pentapeptide that directly and specifically inhibits its ac tivity. PhrA specificity for RapA inhibition is dependent upon the amino ac id sequence of the peptide. Here we show that the pentapeptide affinity for the phosphatase requires a free carboxylate group at the C-terminal amino acid. A free C-terminal carboxylic acid PhrA pentapeptide inhibits RapA pho sphatase activity at a 1: 1 ratio and it is approximately 200 fold more act ive than a C-terminal arn ide peptide. Therefore, coordination of the termi nal carboxylate group appears to be critical for peptide binding to RapA. P ublished by Elsevier Science Inc.