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Publication Abstract from PubMed

The physiological changes that sperm undergo in the female reproductive tract rendering them fertilization-competent constitute the phenomenon of capacitation. Cholesterol efflux from the sperm surface and protein kinase A (PKA)-dependent phosphorylation play major regulatory roles in capacitation, but the link between these two phenomena is unknown. We report that apolipoprotein A-I binding protein (AI-BP) is phosphorylated downstream to PKA activation, localizes to both sperm head and tail domains, and is released from the sperm into the media during in vitro capacitation. AI-BP interacts with apolipoprotein A-I, the component of high-density lipoprotein involved in cholesterol transport. The crystal structure demonstrates that the subunit of the AI-BP homodimer has a Rossmann-like fold. The protein surface has a large two compartment cavity lined with conserved residues. This cavity is likely to constitute an active site, suggesting that AI-BP functions as an enzyme. The presence of AI-BP in sperm, its phosphorylation by PKA, and its release during capacitation suggest that AI-BP plays an important role in capacitation possibly providing a link between protein phosphorylation and cholesterol efflux.

Biochemical and structural characterization of apolipoprotein A-I binding protein, a novel phosphoprotein with a potential role in sperm capacitation.,Jha KN, Shumilin IA, Digilio LC, Chertihin O, Zheng H, Schmitz G, Visconti PE, Flickinger CJ, Minor W, Herr JC Endocrinology. 2008 May;149(5):2108-20. Epub 2008 Jan 17. PMID:18202122^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.