Characterization of Sperm Immobilization Factor from Escherichia coli and Its Receptor to Study the Underlying Mechanism of Sperm Immobilization

Sperm immobilization factor (SIF) was extracted and purified from Escherichia coli filtrate. Characterization of SIF using Liquid chromatography –mass spectrometry (LC-MS) revealed its sequence similarity to chaperone protein HchA of E. coli O157:H7. Further the effect of SIF on sperm functions such as acrosome reaction was studied and the results showed that SIF (500μg/ml) significantly inhibits calcium ionophore induced acrosome reaction. SIF was also found to decrease Mg ++ ATPase activity of spermatozoa from 869.5 (control) to zero at 25μg/ml. The corresponding SIF binding receptor was also isolated and purified. The tryptic peptide analysis of SIF binding receptor by MALDI-TOF (Matrix assisted laser desorption ionizationtime of flight) showed its sequence similarity to chain A structure of human apolactoferrin. Further specificity of SIF and SIF binding receptor was studied by calorimetric studies that showed binding constant (K), enthalpy of binding (ΔH°), free energy (ΔG) and entropy (ΔS) to be 1460/M and -11.7kJ/mole, -18.76 kJ/mole and 22.77 J/moleK, respectively.