2-DIMENSIONAL H-1-NMR STUDY OF A TETRADECAPEPTIDE WITH THE CONSENSUS SEQUENCE ARG(5)-ASP-VAL-ARG-GLY - STRUCTURAL EFFECTS OF THE OUTSIDE SUBSTITUTION SER(12) BY ALA(12)

Conformation of a tetradecapeptide with a RXVRG consensus sequence, Ar g(5)-Asp-Val-Arg-Gly(9), found in several precursors of antibacterian peptides, was investigated in dimethylsulfoxide solution by proton NMR spectroscopy. Complete resonance assignments and conformational param eters were obtained through correlated (COSY) and nuclear Overhauser ( NOESY) techniques. The (3)J(alpha H, beta H) coupling constants and th e intramolecular NOE, NH...beta H, were used to analyse the conformers around the C alpha-C beta bond and, in four cases, to obtain stereosp ecific assignments. Use of restraints derived from NOE connectivities and (3)J(NH, alpha H) coupling constants allows the determination of a range of phi and psi dihedral angles for all the residues in the sequ ence. The present NMR results provide favourable evidence for the form ation of two bends in the consensus sequence of the tetradecapeptide. The first one has most of the features of a Glu(4)- Val(7) beta-turn ( low temperature coefficient of the Val(7)NH chemical shift, Arg(5) alp ha H...Val(7)NH and Asp(6)NH...Val(7)NH NOE correlations). The second one exhibits only the Asp(6) alpha H...Arg(7)NH and Val(7)NH...Arg(8)N H NOE interactions. These consensus sequence organizations proposed we re confirmed by molecular modeling based on low potential energy struc ture on the [4-9] fragment with high agreement of NOE data. Overall, t he substitution of Ser(12) by Ala(12) shifts the conformation of the h ydrophobic moiety [10-14] towards a quite random coil structure in thi s fragment and strongly destabilizes the folded structures of the cons ensus domain where only one NH (Val(7)) is solvent-shielded opposed to three (Asp(6) to Arg(8)) in the [Ser(12)] tetradecapeptide. These con formational changes could be related to the processing enzyme activiti es on these model oligopeptides.