An N-terminal partial sequence of the 13 kDa Pycnopodia helianthoides sperm chemoattractant 'startrak' possesses sperm-attracting activity.

Freshwater extracts of starfish ovaries were used to purify the sperm-attracting peptide 'startrak' from Pycnopodia helianthoides using hydrophobic interaction chromatography and DEAE-high-pressure liquid chromatography. Partially purified attractant had a molecular mass of 13 kDa, estimated from gel filtration and polyacrylamide gel electrophoresis results. The purified attractant was subjected to amino acid analysis and direct sequencing, and was found to consist largely of a single peptide composed of an estimated 127 residues based on a molecular mass of 13kDa. An N-terminal sequence of amino acids from positions 3 to 34 was obtained and synthesized as: NH2-Ala-Glu-Leu-Gly-Leu-Cys-Ile-Ala-Arg-Val-Arg-Gln-Gln-Asn-Gln-Gly-Gln- Asp-Asp-Val-Ser-Ile-Tyr-Gln-Ala-Ile-Met-Ser-Gln-Cys-Gln-Ser-COOH. The synthetic peptide possessed sperm-attracting activity 130 times greater than the activity of partially purified startrak and showed a pattern of species-specificity of sperm chemotaxis similar to that of startrak. Antibody prepared against synthetic peptide removed the sperm-attracting activity from crude and partially purified preparations of startrak. The partial sequence of startrak was not homologous with that of any of the known echinoid sperm motility-activating peptides.