SEQUENTIAL ASSIGNMENTS AND IDENTIFICATION OF SECONDARY STRUCTURE ELEMENTS OF THE COLICIN E9 IMMUNITY PROTEIN IN SOLUTION BY HOMONUCLEAR ANDHETERONUCLEAR NMR

H-1-H-1, H-1-N-15, and H-1-H-1-N-15 multidimensional NMR spectroscopic studies of the 86 amino acid protein that provides immunity against t he DNase action of colicin E9 are reported. Through a combination of 2 D NOESY and TOCSY and 3D TOCSY-HMQC, NOESY-HMQC, and HMQC-NOESY-HMQC e xperiments, almost complete H-1 NMR and backbone N-15 NMR assignments have been obtained, and the secondary structure of the protein has bee n partially elucidated. Approximately 50% of the protein forms three h elices. The specificity determining region of the DNase immunity prote in, identified from previously reported biochemical studies to include residues 32-40, is helical, indicating that the protein-protein inter action involves residues from at least one helix.