title: Novel partners of SPAG11B isoform D in the human male reproductive tract.
abstract: Human sperm-associated antigen 11 (SPAG11) is closely related to beta-defensins in structure, expression, and function. Like the beta-defensins, SPAG11 proteins are predominantly expressed in the male reproductive tract, where their best-known major roles are in innate host defense and reproduction. Although several hypotheses have emerged to describe the evolution of beta-defensin and SPAG11 multifunctionality, few describe these multiple functions in terms of defensin interactions with specific proteins. To gain insight into the protein interaction potentials of SPAG11 and the signaling pathways that SPAG11 may influence, we used a yeast two-hybrid screening of a human testis-epididymis library. The results reveal human SPAG11B isoform D (SPAG11B/D) interactions with tryptase alpha/beta 1 (TPSAB1), tetraspanin 7 (TSPAN7), and attractin (ATRN). These interactions were confirmed by coimmunoprecipitation and glutathione S-transferase affinity matrix binding. SPAG11B/D and the three interacting proteins are expressed in the proximal epididymis, and all function in immunity and fertility pathways. We analyzed the functional consequences of SPAG11B/D interaction with TPSAB1 and showed that SPAG11B/D is both a substrate and a potent inhibitor of TPSAB1 activity. Furthermore, we show that (like SPAG11B/D) TSPAN7 and ATRN are associated with spermatozoa.
authors.affiliation: Departments of Pediatrics and Cell and Developmental Biology, Laboratories for Reproductive Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA. yash@med.unc.edu
authors.forename: Yashwanth
authors.initials: Y
authors.lastname: Radhakrishnan
authors.forename: Katherine G
authors.initials: KG
authors.lastname: Hamil
authors.forename: Jiann-An
authors.initials: JA
authors.lastname: Tan
authors.forename: Gail
authors.initials: G
authors.lastname: Grossman
authors.forename: Peter
authors.initials: P
authors.lastname: Petrusz
authors.forename: Susan H
authors.initials: SH
authors.lastname: Hall
authors.forename: Frank S
authors.initials: FS
authors.lastname: French
mesh_terms: D000954:Antigens, Surface / Q000378:metabolism*; D005837:Genitalia, Male / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D059470:Tetraspanins; D053802:Tryptases / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: C492192:ATRN protein, human; D000954:Antigens, Surface; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; C521209:SPAG11B protein, human; C404405:TSPAN7 protein, human; D059470:Tetraspanins; C546348:TPSAB1 protein, human; D053802:Tryptases