Am. J. Biomed. Sci. 2013, 5(1), 25-33; doi: 10.5099/aj130100025 © 2013 by NWPII. All rights reserved. 25 American Journal of Biomedical Sciences ISSN: 1937-9080 nwpii.com/ajbms Characterization of Sperm Immobilization Factor from Escherichia coli and Its Receptor to Study the Underlying Mechanism of Sperm Immobilization Harpreet Vander, Sonia Gupta, Siftjit Kaur, Kiranjeet Kaur and Vijay Prabha* Department of Microbiology, Panjab University, Chandigarh, India *Corresponding Author: Dr. (Mrs) Vijay Prabha Professor Department of Microbiology Panjab University Chandigarh-160014. India Telephone: 91-172-2534140 Fax: 91-172-2541770 E mail: satishvijay11@yahoo.com Received:19 April 2012; | Revised:18 September 2012; | Accepted: 28 October 2012 Abstract 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 ionization- time 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. Keywords: Escherichia coli, sperm immobilization factor, spermatozoa, receptor, acrosome reaction. 1. Introduction Infections of the male genitourinary tract represent a significant health care problem and account for almost 15% of cases of male infertility [1]. The most discussed and tested microorganism concerning male infertility is Escherichia coli. It is also the principal pathogen causing prostatitis and epididymitis [2]. Diemer et al. [3] have reported negative influence of E. coli on sperm motility which also manifests as