Biochemical characterization of sperm agglutination antigen-1, a human sperm surface antigen implicated in gamete interactions

• Published in: Biology of reproduction 1997-11, Vol.57 (5), p.1136-1144
• Main Authors: DIEKMAN, A. B, WESTBROOK-CASE, V. A, NAABY-HANSEN, S, KLOTZ, K. L, FLICKINGER, C. J, HERR, J. C
• Format: Article
• Language: English
• Subjects: Antibodies, Monoclonal - immunology; Antigens, Surface - chemistry; Antigens, Surface - immunology; Antigens, Surface - metabolism; Biological and medical sciences; Birth control; Detergents - pharmacology; Electrophoresis, Polyacrylamide Gel; Fluorescent Antibody Technique, Direct; Gynecology. Andrology. Obstetrics; Humans; Immunoblotting; In Vitro Techniques; Male; Medical sciences; Membrane Glycoproteins - chemistry; Membrane Glycoproteins - immunology; Membrane Glycoproteins - metabolism; Microscopy, Fluorescence; Other methods of contraception. Sterilization; Periodic Acid; Semen - drug effects; Semen - immunology; Semen - physiology; Sperm Agglutination - immunology; Spermatozoa - drug effects; Spermatozoa - immunology; Spermatozoa - physiology
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod57.5.1136

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.