DELETION OF A SINGLE AMINO-ACID CHANGES THE FOLDING OF AN APAMIN HYBRID SEQUENCE PEPTIDE TO THAT OF ENDOTHELIN

The solution conformations of a hybrid sequence peptide related to the bee venom peptide apamin have been determined using two-dimensional H -1-nmr. Apamin is an 18 amino acid peptide containing a C-terminal hel ix that is stabilized by two disulfide bonds. The deletion of one resi due (K4) of the N-terminal ''scaffold'' region of the apamin sequence results in a helical peptide, but with a change in the pairing of cyst eines to form the disulfide cross links. The new disulfide arrangement is analogous to that of the vasoconstrictor peptide endothelin. Two s ets of nmr resonances were observed for the apamin-deletion (AD) pepti de, due to cis-trans isomerism at the A4-P5 peptide bond. The cis isom er of the AD peptide contains a tight turn in residues 3-6, which is r equired for formation of the alpha-helix in residues 7-15. Nuclear Ove rhauser effects observed for the trans AD peptide are not consistent w ith any single unique fold, indicating the presence of conformational averaging when the peptide adopts the trans form. Distance geometry ca lculations on the cis AD peptide reveal an alpha-helical structure tha t appears to be more like that of apamin than the crystal structure of human endothelin, despite the reversal of the disulfide pattern in th e AD peptide from that of apamin to that of endothelin. (C) 1997 John Wiley & Sons, Inc.