Isolation and partial characterization of an ion channel protein from human sperm membranes

Abstract

Human sperm cells were fractionated and plasma membrane proteins were separated by molecular gel sieving chromatography (Sephacryl S-200 followed by HPLC). A poreforming protein was extracted from sperm cell membranes. The partially purified protein migrated with M r 100,000–110,000, as determined by molecular sieving gel chromatography, and with a M r 90,000 when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. The channel activity was also extracted with Triton X-114, suggesting a hydrophobic nature for this protein. This protein was incorporated into planar lipid bilayers, resulting in the formation of voltage-dependent ion channels. Single channel fluctuations of 130 pS/unit in 0.1 m NaCl were resolved; however, channels preferentially aggregated in triplets having an open state life-time that persisted for several seconds. The channels studied here were more selective for monovalent cations than anions, but also showed some permeability to anions and larger electrolytes, suggesting a large functional pore diameter. The role of this sperm channel in normal sperm physiology and/or fertilization is presently unclear.