title: Acrosome reaction-related steroidal saponin, Co-ARIS, from the starfish induces structural changes in microdomains.
abstract: Cofactor for acrosome reaction-inducing substance (Co-ARIS) is a steroidal saponin from the starfish Asterias amurensis. Saponins exist in many plants and few animals as self-defensive chemicals, but Co-ARIS has been identified as a cofactor for inducing the acrosome reaction (AR). In A. amurensis, the AR is induced by the cooperative action of egg coat components (ARIS, Co-ARIS, and asterosap); however, the mechanism of action of Co-ARIS is obscure. In this study we elucidated the membrane dynamics involved in the action of Co-ARIS. We found that cholesterol specifically inhibited the Co-ARIS activity for AR induction and detected the binding of labeled compounds with sperm using radioisotope-labeled Co-ARIS. Co-ARIS treatment did not reduce the content of sperm sterols, however, the condition was changed and localization of GM1 ganglioside on the periacrosomal region disappeared. We then developed a caveola-breaking assay, a novel method to detect the effect of chemicals on microdomains of culture cell, and confirmed the disturbance of somatic cell caveolae in the presence of Co-ARIS. Finally, by atomic force microscopy observations and surface plasmon resonance measurements using an artificial membrane, we revealed that Co-ARIS colocalized with GM1 clusters on the microdomains. Through this study, we revealed a capacitation-like event for AR in starfish sperm.
authors.affiliation: Department of Biosciences and Informatics, Keio University, Yokohama, Kanagawa, 223-8522, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Naruse
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Suetomo
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Matsubara
authors.forename: Toshinori
authors.initials: T
authors.lastname: Sato
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yanagawa
authors.forename: Motonori
authors.initials: M
authors.lastname: Hoshi
authors.forename: Midori
authors.initials: M
authors.lastname: Matsumoto
mesh_terms: D020101:Acrosome Reaction / Q000187:drug effects*; D000818:Animals; D047271:Asterias / Q000737:chemistry* / Q000187:drug effects*; D001665:Binding Sites; D001681:Biological Assay; D016466:CHO Cells; D021941:Caveolae / Q000187:drug effects / Q000378:metabolism; D002784:Cholesterol / Q000737:chemistry / Q000494:pharmacology*; D006224:Cricetinae; D003412:Cricetulus; D005677:G(M1) Ganglioside / Q000378:metabolism; D007700:Kinetics; D008297:Male; D021962:Membrane Microdomains / Q000737:chemistry* / Q000187:drug effects* / Q000378:metabolism; D008567:Membranes, Artificial; D008968:Molecular Conformation; D012503:Saponins / Q000737:chemistry / Q000494:pharmacology*; D013094:Spermatozoa / Q000187:drug effects / Q000502:physiology; D014316:Tritium / Q000378:metabolism
chemical_list: D008567:Membranes, Artificial; D012503:Saponins; C553681:cofactor for acrosome reaction-inducing substance, Asterias amurensis; D014316:Tritium; D005677:G(M1) Ganglioside; D002784:Cholesterol