Identification of a glycosylated relaxin-like molecule from the male Atlantic stingray, Dasyatis sabina

The alkaline gland fluid of the Atlantic stingray (Dasyatis sabina) contains a molecule that cross-reacts weakly to anti-porcine relaxin antibodies. This material was isolated and purified to homogeneity by reversed-phase high-performance liquid chromatography. In SDS gel electrophoresis, the molecule showed an apparent molecular mass of 13 kDa which upon reduction formed two polypeptide chains of 4 and 9 kDa, respectively. Sequence analyses revealed a 27-amino acid residue A chain and a 54-amino acid residue B chain which contained an N-glycosylation site in position B37. The distribution of the six cysteines and possibly the disulfide bonding is identical to that found in insulins and most relaxins. Although the stingray relaxin-like molecule contains the structurally relevant glycine residues within the A chain, in the midregion of the B chain it has only one of the two requisite binding site arginines, which explains the lack of relaxin bioactivity in standard mammalian assays. Stingray relaxin is the first member of the relaxin family identified in a nonhomeotherm male. Carbohydrate analysis of relaxin revealed an N-linked asialo, agalacto, bisected biantennary, and a core-fucosylated oligosaccharide in the position of Asn B37 which makes it the first reported glycosylated relaxin-like molecule.