title: Biochemical characterization of sperm agglutination antigen-1, a human sperm surface antigen implicated in gamete interactions.
abstract: The anti-sperm monoclonal antibody (mAb) S19 was previously demonstrated to agglutinate human spermatozoa, inhibit sperm penetration of cervical mucus, and inhibit sperm-zona pellucida binding. These results implicated the cognate S19 antigen, designated sperm agglutination antigen-1 (SAGA-1), in gamete interactions and identified SAGA-1 as an attractive candidate for immunocontraceptive development. In the present study, evaluation of sperm agglutination with video microscopy showed that the S19 mAb rapidly and completely agglutinated human spermatozoa in a "tangled" pattern of agglutination. One- and two-dimensional immunoblot analyses identified SAGA-1 as a highly acidic, polymorphic sperm protein with an apparent molecular mass of 15-25 kDa and an isoelectric point of 2.5-3.0. Periodate treatment abolished this immunoreactivity, demonstrating that the S19 mAb reacted with a carbohydrate epitope and indicating that SAGA-1 is a glycoprotein. Absence of S19 immunoreactivity in postvasectomy seminal fluid implicated the testis, epididymis, and/or proximal vas deferens in the expression of SAGA-1. In solubility and phase partitioning assays, SAGA-1 was extracted from spermatozoa in Triton X-114 and exhibited the hydrophobic characteristics of integral and glycosylphosphatidyl inositol-anchored membrane proteins. These results identify SAGA-1 as a hydrophobic, highly acidic sperm glycoprotein that is localized on the entire sperm surface and has potential significance as a target for antibodies that inhibit sperm function and gamete interactions.
authors.affiliation: Center for Recombinant Gamete Contraceptive Vaccinogens, Department of Cell Biology, University of Virginia, Charlottesville 22908, USA.
authors.forename: A B
authors.initials: AB
authors.lastname: Diekman
authors.forename: V A
authors.initials: VA
authors.lastname: Westbrook-Case
authors.forename: S
authors.initials: S
authors.lastname: Naaby-Hansen
authors.forename: K L
authors.initials: KL
authors.lastname: Klotz
authors.forename: C J
authors.initials: CJ
authors.lastname: Flickinger
authors.forename: J C
authors.initials: JC
authors.lastname: Herr
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D000954:Antigens, Surface / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D019085:Fluorescent Antibody Technique, Direct; D006801:Humans; D015151:Immunoblotting; D066298:In Vitro Techniques; D008297:Male; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010504:Periodic Acid; D012661:Semen / Q000187:drug effects / Q000276:immunology / Q000502:physiology; D013073:Sperm Agglutination / Q000276:immunology*; D013094:Spermatozoa / Q000187:drug effects / Q000276:immunology* / Q000502:physiology
chemical_list: D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D003902:Detergents; D008562:Membrane Glycoproteins; D010504:Periodic Acid