Evolution of the sea urchin sperm protein bindin

[摘要] The sperm protein bindin is responsible for the species-specific adhesion of the sperm to the egg. The role ofbindin in the establishment of reproductive isolation in thespecies Strongylocentrotus franciscanus and S.purpuratus isconsidered. Evolutionary changes in the bindin molecule aredescribed from an analysis of new cDNA sequences obtainedfrom the species Strongylocentrotus franciscanus andLytechinus variegatus. These sequences are compared to thepreviously obtained bind in sequence from S.purpuratus. Themiddle third of the mature bindin sequence is highlyconserved in all three species, and the flanking sequencesshare short repeated sequences that vary in number betweenthe species. This sequence comparison identified the regionsof bindin that differ between the species, and that aretherefore likely to be responsible for the species-specificproperties of bindin.The regions of the bindin molecule responsible forforming the contact between the sperm and the egg wereinvestigated by assaying the ability of bindin-derivedpeptides to inhibit fertilization. Twenty-four peptides werestudied: seven based on the Strongylocentrotus purpuratusbindin sequence, eleven based on the S.franciscanus bindinsequence, and six control peptides. Values for IC_(50), theconcentration of peptide required to inhibit 50% of theproductive sperm contacts, were extracted from experimentalmeasurements of the extent of fertilization in the presenceof various concentrations of these peptides. The IC_(50)value averaged 220 µM for the control peptides. Five subregions of bindin are represented by peptides that had IC_(50) values less than 20 µM; the most potent peptide (SfO) had an IC_(50) value of 2.2 µM. Peptide SfR, derived from a region of the S.franciscanus bindin that differs from the S.purpuratus bindin, inhibited fertilization species-specifically. The peptides inhibit fertilization with a steep dose-response relationship, which probably reflects a requirement for the engagement of multiple bindin monomers in the initiation of the sperm-egg bond. These results demonstrate that a few specific regions of the bindin molecule are involved in the sperm-egg contact, and that these regions mediate the species-specificity of the interaction.

[发布机构] University:California Institute of Technology;Department:Biology

[关键词] Biology