Monoclonal antibodies specific for an acetylated form of alpha-tubulin recognize the antigen in cilia and flagella from a variety of organisms.

Abstract

Seven monoclonal antibodies raised against tubulin from the axonemes of sea urchin sperm flagella recognize an acetylated form of .alpha.-tubulin present in the axoneme of a variety of organisms. The antigen was not detected among soluble, cytoplasmic, .alpha.-tubulin isoforms from a variety of cells. The specificity of the antibodies was determined by in vitro acetylation of sea urchin and Chlamydomonas cytoplasmic tubulins in crude extracts. Of all the acetylated polypeptides in the extracts, only .alpha.-tubulin became antigenic. Among Chlamydomonas tubulin isoforms, the antibodies recognize only the axonemal .alpha.-tubulin isoform acetylated in vivo on the .epsilon.-amino group of lysine(s) (L''Hernault, S. W., and J. L. Rosenbaum, 1985, Biochemistry, 24:473-478). The antibodies do not recognize unmodified axonemal .alpha.-tubulin, unassembled .alpha.-tubulin present in a flagellar matrix-plus-membrane fraction, or soluble, cytoplasmic .alpha.-tubulin from Chlamydomonas cell bodies. The antigen was found in protein fractions that contained axonemal microtubules from a variety of sources, including cilia from sea urchin blastulae and Tetrahymena, sperm and testis from Drosophila, and human sperm. In contrast, the antigen was not detected in preparations of soluble, cytoplasmic tubulin, which would not have contained tubulin from stable microtubule arrays such as centrioles, from unfertilized sea urchin eggs, Drosophila embryos, and HeLa cells. Although the acetylated .alpha.-tubulin recognized by the antibodies is present in axonemes from a variety of sources and may be necessary for axoneme formation, it is not found exclusively in any one subset of morphologically distinct axonemal microtubules. The antigen was found in similar proportions in fractions from sea urchin sperm axonemes enriched for central pair or outer doublet B or outer doublet A microtubules. Therefore the acetylation of .alpha.-tubulin does not provide the mechanism that specifies the structure of any one class of axonemal microtubules. Preliminary evidence indicates that acetylated .alpha.-tubulin is not restricted to the axoneme. The antibodies described in this report may allows us to deduce the role of tubulin acetylation in the structure and function of microtubules in vivo.