Testisin (TEST1)

PRSS21 encodes a cell-surface anchored serine protease, which is a member of the trypsin family of serine proteases. It is predicted to be active on peptide linkages involving the carboxyl group of lysine or arginine. The protein localizes to the cytoplasm and the plasma membrane of premeiotic testicular germ cells and it may be involved in progression of testicular tumors of germ cell origin. The deduced 314-amino acid ESP1 precursor protein has a calculated molecular mass of 33.1 kD, and the 273-amino acid active form has a calculated molecular mass of 30.6 kD.

ESP1 contains an N-terminal signal peptide, a propeptide, an active site catalytic triad of conserved his, asp, and ser residues, and a hydrophobic C terminus, which suggests that ESP1 is a membrane-type serine protease.