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

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• 作者：Mar&iacute ; a A. Campanero-Rhodes ; Margarita Mené ; ndez ; José ; L. Sá ; iz ; Libia Sanz ; Juan J. Calvete ; and Dolores Sol&iacute ; s
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：July 11, 2006
• 年：2006
• 卷：45
• 期：27
• 页码：8227 - 8235
• 全文大小：195K
• 年卷期：v.45,no.27(July 11, 2006)
• ISSN：1520-4995

文摘

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, themost abundant porcine spermadhesins, occur in seminal plasma as noncovalent heterodimers devoid ofheparin-binding capability. Of note is the stability of this dimer, which is significantly affected byphysiologically relevant conditions such as Zn²⁺ ions. Here, we show that PSP-I and PSP-II when separatedappear 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 scanningcalorimetry, and circular dichroism analyses. However, Zn²⁺ concentrations in the range of those foundin boar seminal plasma induce the unfolding and self-association of PSP-I, apparently as a consequenceof 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 ofboar seminal plasma, which also exhibit different aggregation states. Thus, the modulation of the structuralorganization and heparin-binding ability of PSP-I by Zn²⁺ might be a physiological phenomenon in seminalplasma.