CHEMICAL-STRUCTURE AND TRANSLATION INHIBITION STUDIES OF THE ANTIBIOTIC MICROCIN C7

Escherichia coil microcin C7 (MccC7) is an antibiotic that inhibits pr otein synthesis in vivo. It is a heptapeptide containing unknown modif ications at the N and C termini (Garcia-Bustos, J. F., Pezzi, N., and Mendez, E. (1985) Antimicrob. Agents Chemoth. 27, 791-797), The chemic al structure of MccC7 has been characterized by use of H-1 homonuclear and heteronuclear (C-13, N-15, P-31) nuclear magnetic resonance spect roscopy as well as mass spectrometry (1177 +/- 1 Dal. The heptapeptide Met-Arg-Thr-Gly-Asn-Ala-Asp is substituted at the N terminus by a N f ormyl group, The C-terminal substituent consists of the phosphodiester of 5'-adenylic acid and n-aminopropanol (AMPap), which is linked via the phosphorus atom to an amide group, thus forming a phosphoramide, T he main chain carbonyl of the C-terminal aspartic acid residue is conn ected via this amide bond to the modified nucleotide unit, MccC7: and the peptide unit inhibit protein translation in vitro while a syntheti c analog of the AMPap substituent is not active, Neither the peptide n or the AMPap molecule has an effect on the growth of MccC7-sensible ce lls, Our results strongly suggest that the peptide is responsible for MccC7 antibiotic activity while the C-terminal substituent is needed f or MccC7 transport. Implications of the structure determined in this w ork for MccC7 synthesis and mode of action are discussed.