Characterization of a coiled filamentous structure, "truncated cone", in the acrosome of abalone sperm.

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Abstract
A filamentous structure in the apex of the acrosome, termed "truncated cone", was isolated from abalone sperm heads, and its structural component was characterized. Observation of the isolated truncated cone fraction by negative staining revealed that the truncated cone was composed of a helically coiled filamentous structure which was resistant to treatment with non-ionic detergent and high salt solutions. SDS PAGE of the isolated truncated cone fraction revealed 3 major polypeptides of 60, 86, and 200 kD. Immunofluorescence microscopy and immunoelectron microscopy using affinity-purified monospecific antibody against the 60 kD protein revealed that the 60 kD protein was localized exclusively to the truncated cone in both the isolated truncated cone fraction and the acrosome-reacted sperm. Immunoblotting analysis showed tht anti-vimentin antibody cross-reacted with this 60 kD protein. These results suggest that the 60 kD protein is a component of the truncated cone, which shares antigenic determinants with vimentin.