title: Equatorin: identification and characterization of the epitope of the MN9 antibody in the mouse.
abstract: Equatorin (MN9 antigenic molecule) is a widely distributed acrosomal protein in mammalian sperm. During the acrosome reaction, some amount of equatorin translocates to the plasma membrane, covering the equatorial region. From the results of studies of both in vitro and in vivo fertilization inhibition using the MN9 antibody, equatorin has been suggested to be involved in fusion with the oolemma. In the present study, we cloned equatorin and, using mass spectrometry and carbohydrate staining, found it to be a highly glycosylated protein. Equatorin is a sperm-specific type 1 transmembrane protein, and glycosidase treatment and recombinant protein assays verified that it is an N,O-sialoglycoprotein. In addition, the gamete interaction-related domain recognized by the MN9 antibody is posttranslationally modified. The modified domain was identified near threonine 138, which was most likely to be O-glycosylated when analyzed by amino acid substitution, dephosphorylation, and O-glycosylation inhibitor assays. Immunogold electron microscopy localized the equatorin N-terminus, where the MN9 epitope is present, on the acrosomal membrane facing the acrosomal lumen. These biochemical properties and the localization of equatorin are important for further analysis of the translocation mechanism leading to gamete interaction.
authors: Department of Anatomy and Developmental Biology, Chiba University Graduate School of Medicine, Chiba, Japan.
authors: Kenji
authors: K
authors: Yamatoya
authors: Keiichi
authors: K
authors: Yoshida
authors: Chizuru
authors: C
authors: Ito
authors: Mamiko
authors: M
authors: Maekawa
authors: Mitsuaki
authors: M
authors: Yanagida
authors: Kenji
authors: K
authors: Takamori
authors: Hideoki
authors: H
authors: Ogawa
authors: Yoshihiko
authors: Y
authors: Araki
authors: Kenji
authors: K
authors: Miyado
authors: Yoshiro
authors: Y
authors: Toyama
authors: Kiyotaka
authors: K
authors: Toshimori
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000941:Antigens / Q000032:analysis* / Q000378:metabolism; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D003001:Cloning, Molecular; D024202:Electrophoretic Mobility Shift Assay; D004822:Epididymis / Q000378:metabolism; D000939:Epitopes / Q000032:analysis*; D008297:Male; D013058:Mass Spectrometry; D051379:Mice; D008813:Mice, Inbred ICR; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013737:Testis / Q000378:metabolism
chemical_list: D000941:Antigens; D000939:Epitopes; D012333:RNA, Messenger