Binding of mannose-6-phosphate and heparin by boar seminal plasma PSP-II, a member of the spermadhesin protein family.
PSP-I/PSP-II, a heterodimer of glycosylated spermadhesins, is the major component of boar seminal plasma. Similarly to other spermadhesins, the PSP-II subunit is a lectin which displays heparin- and zona pellucida glycoprotein-binding activities. We have investigated the ligand binding capabilities of the heterodimer and the isolated subunits using several polysaccharides, glycoproteins, and phospholipids. PSP-II binds the sulfated polysaccharides heparin and fucoidan in a dose-dependent and seemingly-specific manner. In addition, PSP-II binds oligosaccharides containing exposed mannose-6-phosphate monoester groups and the binding is selectively inhibited by mannose-6-phosphate and glucose-6-phosphate. Inhibition experiments indicate that binding of PSP-II to sulfated polysaccharides and mannose-6-phosphate-containing oligosaccharides involves distinct but possibly overlapping binding sites. Heterodimer formation with PSP-I abolishes both the heparin and the mannose-6-phosphate binding capabilities, suggesting that the corresponding sites may be located at the dimer interface. Using the crystal structure of PSP-I/PSP-II heterodimer as a template, we have explored possible binding sites which satisfy the observed binding characteristics. In the proposed models, PSP-II Arg43 appears to play a pivotal role in both heparin- and mannose-6-phosphate-complexation as well as in heterodimer formation.
Instituto de Química Física Rocasolano, C.S.I.C., Madrid, Spain. d.solis@iqfr.csic.es
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Solís
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Romero
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Jiménez
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Díaz-Mauriño
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Calvete
D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D019281:Dimerization; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D006493:Heparin / Q000378:metabolism*; D037102:Lectins / Q000737:chemistry; D008360:Mannosephosphates / Q000378:metabolism*; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D012661:Semen / Q000378:metabolism*; D029607:Seminal Vesicle Secretory Proteins; D013552:Swine
D006023:Glycoproteins; D037102:Lectins; D008360:Mannosephosphates; D029607:Seminal Vesicle Secretory Proteins; C074521:seminal vesicle secretory protein II, porcine; C074520:seminal vesicle secretory protein 109, porcine; C027693:mannose-6-phosphate; D006493:Heparin; D003577:Cytochrome P-450 Enzyme System