Affinity labeling of a tyrosine residue in the ATP binding site of the recA protein from Escherichia coli with 5'-p-fluorosulfonylbenzoyladenosine

Abstract

We have covalently modified the recA protein from Escherichia coli with the adenine nucleotide analog 5'-p-fluorosulfonylbenzoyladenosine (5'-FSBA). The rate at which the protein is modified shows a sigmoidal dependence on the concentration of 5'-FSBA suggesting that binding of the analog is characterized by positive cooperativity. Covalent modification of the protein results in irreversible inactivation of its single-stranded DNA-dependent ATPase activity such that 100% inactivation is achieved when 25% of the enzyme monomers have been modified. Attachment of 5'-FSBA is specific for the ATP-binding site of recA protein as judged by the following criteria: (i) attachment of the affinity label to the protein appears to saturate at 1 mol of 5'-FSBA/mol of protein; (ii) binding of 5'-FSBA to recA protein is inhibited by ATP and competitive inhibitors of its ATP hydrolytic activity, e.g. adenosine-5'-O-(thiotriphosphate), ADP, UTP, and GTP, but not by adenosine; (iii) attachment of 5'-FSBA to the protein occurs at a single site as determined by high pressure liquid chromatography peptide separation. Following trypsin digestion of recA protein that had been covalently modified with [3H]5'-FSBA we isolated a single labeled peptide (T31) containing the exclusive site of 5'-FSBA attachment. A secondary proteolytic digestion was performed on both 5'-FSBA modified T31 and unmodified T31 using Staphylococcus aureus V8 protease, and by comparison of the amino acid compositions of the resulting peptides we identified Tyr-264 as the exclusive site of 5'-FSBA attachment in recA protein.