The amino acid sequence of AQN‐3, a carbohydrate‐binding protein isolated from boar sperm Location of disulphide bridges

Abstract

Gamete recognition and adhesion are essential steps in fertilization. Among others, carbohydrate-binding proteins on the sperm surface have been recoenized to nlav a central role in the initial interaction of the male aamete with comnonents of the zona pcllucida of the homologous investing oocyte. We have isolated several members of a carbohydrate-and zoia pellucida-binding protein family from ejaculated sperm. Here we report the biological origin and structural characterization of AQN-3, a component of this carbohydrate-binding family. The molecular weight of purified AQN-3 was determined by plasma desorption mass spectrometry. The protein was chemically and enzymatically degraded, the proteolytic fragments isolated and characterized by N-terminal sequencing and fast atom bombardment mass spectrometry. In this manner we established the complete amino acid sequence of AQN-3 and the location of its two disulphide bonds. No analogous protein sequence could be found in the MIPS protein sequence data bank, indicating that AQNJ may belong to a novel mammalian carbohydrate-binding protein family.

Mapping the heparin‐binding domain of boar spermadhesins

“…Peptide sequences were aligned in the amino acid sequences of AWN [12], PSP-I [13,14], AQN-1 [15], AQN-3 [16], and seminal plasma trypsin inhibitor [17].…”

“…Fragments C-3, C-10, C-l, and C-7 were derived from the N-terminal region of AQN-I, PSP-I, AQN-3, and AWN, respectively. Fragments C-10 and C-7 contained each two disulphide-bonded peptides, whereas C-3 and C-1 corresponded to the loop region formed by the conserved disulphide bridge between the first two cysteines of the proteins [12,13,15,16]. Fragments C-4, C-8, and C-11, contained each two peptides disulphide-bonded by the second conserved cystine of spermadhesins AQN-1 [15], PSP-I [13], and AWN [12].…”

“…Peptides were aligned in the amino acid sequences of AWN [12], PSP-I [13,14], AQN-I [15], AQN-3 [16], and acrosin inhibitor (AI) [17]. , PSP-I [13,14], AQN-3 [16], and AWN [12] showing the chymotryptic (C-) and elastase-derived (E-) fragments obtained by in situ proteolysis of heparin-bound seminal plasma proteins.…”

“…, PSP-I [13,14], AQN-3 [16], and AWN [12] showing the chymotryptic (C-) and elastase-derived (E-) fragments obtained by in situ proteolysis of heparin-bound seminal plasma proteins. The location of overlapping synthetic peptides PI-P13 of AWN employed to determine heparin-binding capability and AWN-heparin-binding inhibitory activity are shown beneath the AWN sequence.…”

Cloning of boar SPMI gene which is expressed specifically in seminal vesicle and codes for a sperm motility inhibitor protein

“…The hydropathy profile of the predicted SPMI protein suggests that the boar SPMI is a rather hydrophilic protein (Fig. 2). [12,13] and SPMI protein predicted by cloned eDNA sequence Fig. 3 shows that AQN-3 and SPMI are very homologous in amino acid sequence with a homology index of 97%.…”