Cylicin 2 (CYLC2)

The cytoskeletal calyx of mammalian sperm heads surrounding the basolateral part of the nucleus contains 2 kinds of basic proteins: cylicins, or multiple-band polypeptides, and calicin.

Like cylicin-1, the deduced cylicin-2 protein has a high content of charged amino acids, an abundance of lys-lys-asp tripeptides, and repetitive units that are predicted to form alpha helices. The authors attributed this discrepancy to the protein's unusually high concentration of charged amino acids. Both bovine cylicin genes are expressed specifically in testis. The predicted 348-amino acid protein contains 52% charged amino acids and has a calculated pI of 10.53. The N- and C-terminal regions of bovine and human cylicin-2 are highly homologous, but the human protein has several large deletions in the central region.