157 - Gametolysin

Abstract

This chapter describes the activity, specificity and structural chemistry of gemetolysin. Gametolysin consists of a 28 amino acid signal peptide, a 155 amino acid propeptide and a 455 amino acid mature peptide. A potential site for autocatalytic activation is contained in the middle of the propeptide and a zinc-binding site is found within the mature peptide; both sites are similar to those in mammalian collagenases. A putative calcium-binding site is present in the near C-terminal region of the mature peptide. The active enzyme secreted into the mating medium is a glycoprotein of 60–62 kDa, pi 6.5. A proenzyme with a slightly higher molecular mass than the active enzyme is found in gametes and also in vegetative cells. The proenzyme, which has been purified from both vegetative and gametic cells, contains a 25-amino acid propeptide at the N-terminus of the mature peptide. The proenzyme of gametolysin exists not only in gametes but also in the periplasm of vegetative cells. Steady-state levels of mRNA and proenzyme increase markedly during growth and mitotic cell division in the vegetative cell cycle.