Polypeptide chains containing D-γ-hydroxyvaline

Life has an unexplained and distinct L-homochirality. Proteins typically incorporate only L-amino acids into their sequences. In the present study, D-Val and D-gamma-hydroxyvaline (D-Hyv; (V) under bar*) have been found within ribosomally expressed polypeptide chains. Four conopeptides were initially isolated, gld-(V) under bar*/gld-(V) under bar*(/) from the venom of Conus gladiator and mus-(V) under bar*/mus-(V) under bar*' from the venom of Conus mus. Their complete sequences (gld-(V) under bar*/gld-(V) under bar*' = Ala-Hyp-Ala-Asn-Ser-D-Hyv-Trp-Ser and mus-(V) under bar*/mus-(V) under bar*' = Ser-Hyp-Ala-Asn-Ser-D-Hyv-Trp-Ser) were determined by a combination of nano/pico-NMR and MS/MS methods. The amino acid triad that contains the gamma-hydroxylated residue, Ser-D-Hyv-Trp, is a novel structural motif that is stabilized by specific interactions between the D-amino acid and its neighboring L-counterparts. These interactions inhibit lactonization, a peptide backbone scission process that would normally be initiated by gamma-hydroxylated residues. Conopeptides possessing the Ser-D-Hyv-Trp motif have been termed gamma-hydroxyconophans. We have also isolated analogous conopeptides (gld-(V) under bar and mus-(V) under bar) containing D-Val instead of D-Hyv; these are termed conophans. gamma-Hydroxyconophans and conophans are particularly atypical because (i) they are not constrained as most conopeptides, (ii) they are extremely short in length, (iii) they have a high content of hydroxylated residues, and (iv) their sequences have no close match with other peptides in sequence databases. Their modifications appear to be part of a novel hyperhydroxylation mechanism found within the venom of cone snails that enhances neuronal targeting. The finding of D-Val and D-Hyv within this family of peptides suggests the existence of a corresponding D-stereospecific enzyme capable of D-Val oxidation.