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A pH Switch Regulates the Inverse Relationship between Membranolytic and Chaperone-like Activities of HSP-1/2, a Major Protein of Horse Seminal Plasma

Kumar, C. Sudheer, Swamy, Musti J.
Biochemistry 2016 v.55 no.26 pp. 3650-3657
cholesterol, choline, conjugated linoleic acid, horses, hydrophobicity, models, pH, phospholipids, plasma membrane, proteins, seminal plasma, sperm capacitation, spermatozoa
HSP-1/2, a major protein of horse seminal plasma binds to choline phospholipids present on the sperm plasma membrane and perturbs its structure by intercalating into the hydrophobic core, which results in an efflux of choline phospholipids and cholesterol, an important event in sperm capacitation. HSP-1/2 also exhibits chaperone-like activity (CLA) in vitro and protects target proteins against various kinds of stress. In the present study we show that HSP-1/2 exhibits destabilizing activity toward model supported and cell membranes. The membranolytic activity of HSP-1/2 is found to be pH dependent, with lytic activity being high at mildly acidic pH (6.0–6.5) and low at mildly basic pH (8.0–8.5). Interestingly, the CLA is also found to be pH dependent, with high activity at mildly basic pH and low activity at mildly acidic pH. Taken together the present studies demonstrate that the membranolytic and chaperone-like activities of HSP-1/2 have an inverse relationship and are regulated via a pH switch, which is reversible. The higher CLA observed at mildly basic pH could be correlated to an increase in surface hydrophobicity of the protein. To the best of our knowledge, this is the first study reporting regulation of two different activities of a chaperone protein by a pH switch.