Conserved beta-tubulin binding domain for the microtubule-associated motors underlying sperm motility and fast axonal transport.

An antiserum against tubulin, NS20, has been previously shown to inhibit anterograde and retrograde axonal transport by 50% in vivo and in vitro. We report here that Protein A purified NS20 antibodies also attenuate sperm motility by 50% in demembranated sea urchin sperm. This inhibition is absorbed out by preincubating the NS20 antibodies with a biochemically purified porcine microtubule preparation, with recombinant Trypanosoma beta- (but not alpha-) tubulin and most specifically, with a 37 amino acid (a.a.) synthetic peptide corresponding to a domain near (but not including) the porcine beta-tubulin C terminus. Furthermore, addition of this beta-tubulin peptide alone is sufficient to attenuate motility by 50% in demembranated sperm, indicating that this critical 37a.a. NS20 antigen is a motor binding domain. Together, the results suggest that at least two phenotypically distinct forms of microtubule-based motility, axonal transport and flagellar beating, are homologous at the fundamental level of the microtubule domains (the beta-tubulin peptide and we suggest a distinct but similarly located alpha-tubulin domain) mediating the attachment of tubulin-associated motors.