title: Galectin-3 is associated with prostasomes in human semen.
abstract: Galectin-3 is a beta-galactoside-binding protein involved in immunomodulation, cell interactions, cancer progression, and pathogenesis of infectious organisms. We report the identification and characterization of galectin-3 in human semen. In the male reproductive tract, the approximately 30 kDa galectin-3 protein was identified in testis, epididymis, vas deferens, prostate, seminal vesicle, and sperm protein extracts. In seminal plasma, galectin-3 was identified in the soluble fraction and in prostasomes, cholesterol-rich, membranous vesicles that are secreted by the prostate and incorporated into seminal plasma during ejaculation. Two-dimensional immunoblot analysis of purified prostasomes identified five galectin-3 isoelectric variants with a pI range of 7.0 to 9.2. Affinity purification and tandem mass spectrometry of beta-galactoside-binding proteins from prostasomes confirmed the presence of galectin-3 in prostasomes and identified a truncated galectin-3 variant. The intact galectin-3 molecule contains a carbohydrate recognition domain and a non-lectin domain that interacts with protein and lipid moieties. The identification of a monovalent galectin-3 fragment with conserved carbohydrate-binding activity indicates the functional relevance of this truncation and suggests a regulatory mechanism for galectin-3 in prostasomes. Surface biotinylation studies suggested that galectin-3 and the truncated galectin-3 variant are localized to the prostasome surface. Prostasomes are proposed to function in immunosuppression and regulation of sperm function in the female reproductive tract, are implicated in facilitating sexually-transmitted infections, and are indicated in prostate cancer progression. Given the overlap in functional significance, the identification of galectin-3 in prostasomes lays the groundwork for future studies of galectin-3 and prostasomes in reproduction, disease transmission, and cancer progression.
authors.affiliation: Department of Biochemistry and Molecular Biology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Jones
authors.forename: Sarika
authors.initials: S
authors.lastname: Saraswati
authors.forename: Ashley S
authors.initials: AS
authors.lastname: Block
authors.forename: Cheryl F
authors.initials: CF
authors.lastname: Lichti
authors.forename: Maha
authors.initials: M
authors.lastname: Mahadevan
authors.forename: Alan B
authors.initials: AB
authors.lastname: Diekman
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D019921:Biotinylation; D002499:Centrifugation, Density Gradient; D002850:Chromatography, Gel; D005697:Galactosides / Q000378:metabolism; D037502:Galectin 3 / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D005837:Genitalia, Male / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008297:Male; D008566:Membranes; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D022142:Secretory Vesicles / Q000378:metabolism*; D012661:Semen / Q000737:chemistry / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D013499:Surface Properties; D053719:Tandem Mass Spectrometry; D014461:Ultracentrifugation
chemical_list: D000911:Antibodies, Monoclonal; D005697:Galactosides; D037502:Galectin 3