X-Ray Crystallographic Analysis of Boar PSP-I/PSP-II Complex

PSP-I and PSP-II are major proteins isolated from porcine seminal plasma (PSP). Both, PSP-I (109 amino acids) and PSP-II (116 amino acids) are glycoproteins and display site heterogeneity, i.e. they contain a single N-glycosylated asparagine residue (PSP-I N50 and PSP-II N98) which accomodates different glycan moieties (Calvete et al.,1993; Calvete et al., 1995а) PSP-II forms a non-covalent heterodimer with certain glycoforms of PSP-I (Calvete et al., 1995а). Both subunits of the heterodimer belong to the spermadhesin protein family (Calvete et al., 1995b). In the pig, this group of proteins include sperm surface-associated lectins that are thought to mediate the initial binding of spermatozoa to carbohydrate structures of zona pellucida glycoproteins (Dostalova et al., 1995; Calvete et al., 1996). The PSP-I/PSP-III heterodimer contains a binding site for zona pellucida glycoproteins located around PSP-II N50 (Calvete et al., 1995а) The zona pellucida-binding characteristics and easiness of isolation of PSP-I/PSP-II (Calvete et al., I 995a), makes this spermadhesin a paradigm for studying protein-carbohydrate interactions involved in gamete recognition. Moreover, spermadhesins are composed of a single CUB domain architecture (Bork et al., 1993) whose three-dimensional structure remains to be determined.