Investigation of an octapeptide inhibitor of Escherichia coli ribonucleotide reductase by transferred nuclear Overhauser effect spectroscopy.

Several peptides contained within the C-terminal sequence of the B2 subunit of Escherichia coli ribonucleotide reductase (RNR) were investigated for their ability to inhibit the enzyme, presumably by interfering with association of the B1 and B2 subunits. AcYLVGQIDSE, corresponding by sequence homology to a nonapeptide that inhibits herpes simplex RNR [Gaudreau et al. (1987) J. Biol. Chem. 262, 12413] shows no inhibition of the E. coli enzyme (IC50 greater than 3 mM), whereas AcDDLSNFQL, the C-terminal octapeptide of the E. coli B2 subunit, is a noncompetitive inhibitor (Ki = 160 microM). Neither bradykinin (RPPGFSPFR) nor the pentapeptide AcSNFQL inhibits the E. coli enzyme. Transferred nuclear Overhauser enhancement spectroscopy was used to probe the conformation of AcDDLSNFQL when it is bound to the B1 subunit. These experiments suggest that the peptide adopts a turn in the region of Asn5 and Phe6 and that a hydrophobic cluster of the phenylalanine and leucine side chains is involved in the interaction surface.