Isolation and characterization of a rabbit sperm tail protein

Rabbit sperm tails were obtained by a nitrogen cavitation procedure and separated by discontinuous sucrose gradient centrifugation. Proteins were extracted from sperm tails with 3[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate (CHAPS) and separative disk electrophoresis and DEAE-trisacryl column chromatography. A protein with an estimated mol wt of 20.1 +/- 1.1 kD was isolated and found to be homogeneous by SDS-PAGE and designated as rSMP-B. The isoelectric point of rSMP-B was in the range of pH 4.4-4.7. The amino acid composition was determined, and glycine was identified as the N-terminal residue. Antisera were raised against purified rSMP-B. Using a peroxidase-antiperoxidase method, the rSMP-B antigen was located on the surface of the midpiece and tail of the sperm. Testis sections showed intense staining of late spermatids located within the seminiferous tubules. Adult male rabbits were inoculated with rSMP-B protein and Freund's adjuvant. The testis and epididymis of the immunized animals showed absence of sperm. The immunolocalization findings and the immunization data suggest that rSMP-B is formed in late spermatid and that it is an essential structural component of sperm.