Characterization of two glycosylated boar spermadhesins.
Boar spermadhesins AQN-1, AQN-3 and AWN form a recently described protein family, synthesized by the sexual accessory glands, and become associated with the sperm head upon ejaculation. They contain 109-133 amino acid residues, two conserved disulphide bridges, are not glycosylated, and have 40-60% primary structure identity. These boar polypeptides are multifunctional proteins, which possess heparin-, serine-protease-inhibitor- and/or zona-pellucida-glycoprotein-binding capability and have, therefore, been implicated in sperm capacitation and sperm-oocyte attachment. AQN-2 (18-20 kDa), however, is unique among boar spermadhesins in that it is the only member of the family which is known to be glycosylated and which possesses weak zona-pellucida-binding but not seminal-plasma-inhibitor-binding ability. In this study we report the structural and functional characterization of the two glycoproteins contained in the AQN-2 fraction. One component is identical with PSP-I, a major porcine seminal plasma protein whose function has not yet been identified, while the second protein is a glycosylated isoform of AQN-3. Here we show that the inability of the glycosylated boar spermadhesins to bind seminal-plasma protease inhibitors as well as the weak binding of glycosylated AQN-3 to zona pellucida glycoproteins is due to the presence of the oligosacharide chain on a conserved asparagine residue. This indicates that modification of a spermadhesin polypeptide framework may serve to modulate its ligand-binding capabilities.
Calvete
J J
JJ
Institut für Reproduktionsmedizin, Tierärztliche Hochschule Hannover, Germany.
Solís
D
D
Sanz
L
L
Díaz-Mauriño
T
T
Schäfer
W
W
Mann
K
K
Töpfer-Petersen
E
E
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000378:metabolism*; D004527:Egg Proteins; D006031:Glycosylation; D006493:Heparin / Q000378:metabolism; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism; D008969:Molecular Sequence Data; D011956:Receptors, Cell Surface; D029589:Seminal Plasma Proteins; D017386:Sequence Homology, Amino Acid; D015842:Serine Proteinase Inhibitors / Q000378:metabolism; D013094:Spermatozoa / Q000378:metabolism*; D013552:Swine; D000072216:Zona Pellucida Glycoproteins
D002352:Carrier Proteins; D015815:Cell Adhesion Molecules; D004527:Egg Proteins; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D029589:Seminal Plasma Proteins; D015842:Serine Proteinase Inhibitors; D000072216:Zona Pellucida Glycoproteins; C425042:spermadhesin; D006493:Heparin