Cell biology of acrosomal proteins: Zellbiologie akrosomaler Proteine

Abstract

Acrosin is a multifunctional enzyme combining several functional properties within a single molecule: the catalytic triad of the proteinase, hydrophobic domains responsible for the special membrane-associating character of the enzyme and the carbohydrate binding sites by which the molecule can bind to the zona pellucida. Acrosin occurs in the sperm acrosome as an inactive precursor, proacrosin, with a molecular mass of 53-55 kDa. Proacrosin is activated by a single proteolytic clip between Arg23 and Val24 generating the high molecular mass acrosin. The activation of proacrosin to the biologically active enzyme which occurs concomitantly with the acrosome reaction appears to be regulated on and by the zona pellucida. It is hypothesized that alternating cycles of binding to the zona, digestion of the zona and release from the zona together with the forward motility of the spermatozoon would be required to achieve penetration. Zusammenfassung. Acrosin ist ein multifunktionelles Enzym, das in sich verschiedeneEigenschaften kombiniert: die katalytische Triade einer Proteinase, hydrophobe Domanen, die fur die spezielle Membran-Affinitat wesentlich sind und Kohlenhydrat-Bindungsstellen, uber die das Enzym an der Zona pellucida binden kann. Acrosin kommt im Spermien-Akrosom als inaktive Vorstufe, Proacrosin, mit einer molekularen Masse von 53-55 kDa vor. Proacrosin wird durch einen proteolytischen Schnitt zwischen Arg23 und Val24 aktiviert und bildet das hohermolekulare Akrosin. Die Aktivierung von Proacrosin zum biologisch aktiven Enzym verlauft parallel zur akrosomalen Reaktion und scheint durch und an der Zona pellucida reguliert zu werden. Es wird hypothetisch angenommen, daB alternierende Zyklen von Bindung an der Zona, Verdauung des Zonamaterials und Freisetzung von der Zona gemeinsam mit der Vorwartsmotilitat der Spermien fur die Penetration erforderlich sind. Acrosomal proteins 111

Moonlighting proteins in sperm–egg interactions

“…To date, several sperm proteins have been described as ZP glycoprotein receptors in different species, such as acrosin, fertilin, Izumo and a disintegrin and metalloproteinase (ADAM) [1][2][3]. However, implication of these proteins has rarely been demonstrated in humans.…”

“…Key words: antisperm antibody, gamete interaction, moonlighting protein, sperm-egg interaction, sperm protein.Abbreviations: ALDOA, aldolase A; ASA, antisperm antibody; GSTM, GST Mu; hrZP, human recombinant ZP; PSA, Pisum sativum agglutinin; TPI, triose phosphate isomerase; VDAC2, voltagedependent anion channel 2; ZP, zona pellucida 1. To whom correspondence should be addressed (email francois.petit@abc.aphp.fr).…”