Conformational energy analysis of the pentapeptide Ac-Arg-Asn-Cys-Tyr-Asn-NMA from alpha 1-purothionin

Conformational energy analyses were carried out on the pentapeptide RNCYN (Ac-Arg-Asn-Cys-Tyr-Asn-NMA) and on related peptides. RNCYN is a highly conserved amino acid sequence in thionins and viscotoxins. The conformation of the pentapeptide was calculated to be an amphipathic alpha-helix, with the tyrosine and cysteine on the nonpolar side of the helix and the arginine and both asparagines on the polar side. Our results are inconsistent with the conformation determined using the Chou-Fasman prediction method, but are consistent with the conformation determined experimentally (using n.m.r.) for this pentapeptide sequence in alpha 1-purothionin.