THE PROTEIN COMPLEXITY OF THE CYTOSKELETON OF BOVINE AND HUMAN SPERM HEADS - THE IDENTIFICATION AND CHARACTERIZATION OF CYLICIN-II

The cytoskeletal calyx of mammalian sperm heads surrounding the basola teral part of the nucleus contains two kinds of basic proteins: Calici n, a polypeptide of approximate M(r) 60,000 as estimated from SDS-PAGE , and the group of the very basic cylicins (pI > 10.0), formerly desig nated as ''multiple-band polypeptides.'' Recently, bovine cylicin I ha s been cDNA cloned and identified as a new type of a cytoskeletal prot ein, which contains numerous Lys-Lys-Asp tripeptides accumulated in ni ne central repetitive units predicted to form alpha-helices. We now re port the cDNA cloning and localization of a second species of cylicin, bovine cylicin II, present in bovine and human sperm heads: Cylicin I I (488 amino acids, M(r) 53,561, pI 10.55) shows the same prominent mo lecular characteristics as cylicin I, including a high content of char ged amino acids, the abundance of Lys-Lys-Asp tripeptides, and repetit ive units of presumably alpha-helical configuration, but also presents some differences. As with cylicin I mRNA, the 2.6-kb mRNA has also be en shown to be specifically expressed in testis. The possible existenc e of a larger cylicin multigene family and its contribution to the cyt oskeleton and the morphogenesis of the sperm head are discussed. (C) 1 995 Academic Press, Inc.