Biochemical characterization of a glycosylphosphatidylinositol-linked hyaluronidase on mouse sperm.
On the basis of DNA homology to bee venom hyaluronidase, it was recently suggested that the GPI-linked mammalian sperm antigen, PH-20, may function as a cell surface hyaluronidase [Gmachl, M., & Kreil, G. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 3569-3573]. We have quantified the activity of the soluble acrosomal hyaluronidase of mouse sperm and further demonstrate the existence of a membrane-bound hyaluronidase, detected on both acrosome-intact and acrosome-reacted mouse sperm, distinct from the soluble form of the enzyme. The membrane-bound hyaluronidase was specifically released by PI-PLC, indicating that it is GPI linked. Acrosome-intact and acrosome-reacted sperm released several polypeptides (68, 44, 39, 34, 17, and 15 kDa) when treated with PI-PLC. In addition, GPI-linked polypeptides unique to acrosome-intact or to acrosome-reacted sperm were identified. Fractionation of the PI-PLC-released components from acrosome-reacted sperm using size exclusion chromatography revealed a single peak of hyaluronidase activity which comigrates with a 68 kDa GPI-linked protein present in these fractions. Taken together, these data demonstrate the existence of at least two isoforms of hyaluronidase: a soluble form within the acrosomal vesicle which is released during acrosomal exocytosis and a GPI-linked form which is present on the surface of both acrosome-intact and acrosome-reacted sperm. Both forms may be necessary for successful penetration of the extracellular vestments that surround the egg prior to fertilization.
Thaler
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Department of Biology, University of California, Riverside 92521, USA.
Cardullo
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D000177:Acrosome / Q000201:enzymology; D000818:Animals; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000201:enzymology; D017261:Glycosylphosphatidylinositols; D006821:Hyaluronoglucosaminidase / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D008297:Male; D051379:Mice; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases; D013094:Spermatozoa / Q000166:cytology / Q000201:enzymology*
D017261:Glycosylphosphatidylinositols; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D006821:Hyaluronoglucosaminidase; D043265:Phosphatidylinositol Diacylglycerol-Lyase