Zinc ions induce the unfolding and self-association of boar spermadhesin PSP-I, a protein with a single CUB domain architecture, and promote its binding to heparin.
Spermadhesins are a family of seminal plasma proteins composed of a single CUB domain, which appear to be involved in various aspects of the fertilization process in pigs. PSP-I and PSP-II, the most abundant porcine spermadhesins, occur in seminal plasma as noncovalent heterodimers devoid of heparin-binding capability. Of note is the stability of this dimer, which is significantly affected by physiologically relevant conditions such as Zn2+ ions. Here, we show that PSP-I and PSP-II when separated appear to conserve the overall fold of the CUB domain observed in the crystal structure of the PSP-I/PSP-II heterodimer, as concluded from gel filtration, analytical ultracentrifugation, differential scanning calorimetry, and circular dichroism analyses. However, Zn2+ concentrations in the range of those found in boar seminal plasma induce the unfolding and self-association of PSP-I, apparently as a consequence of the exposure of hydrophobic core residues, whereas they have no effect on PSP-II. Remarkably, Zn2+-denatured and self-associated (but not structured monomeric) PSP-I is retained on a heparin column, resembling the behavior of free PSP-I and homologous spermadhesins of the heparin-binding fraction of boar seminal plasma, which also exhibit different aggregation states. Thus, the modulation of the structural organization and heparin-binding ability of PSP-I by Zn2+ might be a physiological phenomenon in seminal plasma.
Campanero-Rhodes
María A
MA
Instituto de Química Física Rocasolano, CSIC, Serrano 119, 28006 Madrid, Spain.
Menéndez
Margarita
M
Saiz
José L
JL
Sanz
Libia
L
Calvete
Juan J
JJ
Solís
Dolores
D
D000818:Animals; D002152:Calorimetry, Differential Scanning; D002413:Cations, Divalent / Q000737:chemistry; D002846:Chromatography, Affinity; D019281:Dimerization; D006493:Heparin / Q000737:chemistry; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012661:Semen / Q000737:chemistry / Q000378:metabolism; D029607:Seminal Vesicle Secretory Proteins / Q000737:chemistry* / Q000187:drug effects; D034421:Sus scrofa / Q000378:metabolism; D014461:Ultracentrifugation; D015032:Zinc / Q000737:chemistry* / Q000494:pharmacology
D002413:Cations, Divalent; D029607:Seminal Vesicle Secretory Proteins; C074521:seminal vesicle secretory protein II, porcine; C074520:seminal vesicle secretory protein 109, porcine; D006493:Heparin; D015032:Zinc