Evidence that the lizard helospectin peptides are O-glycosylated

Six forms of helospectin (a vasoactive intestinal peptide analogue) were pu rified from the venom of the Heloderma horridum lizard. Their identificatio n was performed by combining sequencing by automated Edman degradation and electrospray mass spectrometry analysis on the complete peptides and their tryptic fragments. The products resulting from the action of an O-glycosida se were also analysed. Two forms were identified as the previously named Hs 1 and Hs2 of 38 and 37 amino-acid residues, respectively. Two forms corresp onded to Hs1 and Hs2 O-glycosylated by a N-acetylhexosamine-hexose motif at tached to the Ser32 residue. Two other forms were not completely characteri zed but might correspond to the O-glycosylated forms bearing a phosphate or a sulfate group. The glycosylation did not affect the capacity of the helo spectins to recognize and to activate the human and the rat VPAC(1) and VPA C(2) receptors.