To characterize the CD4-independent HIV-binding protein of 160kDa on human spermatozoa.
The N-terminal amino acid sequence of the 160kDa protein and its peptide obtained by tryptic digestion were determined. Polymerase chain reaction amplification of human testicular cDNA was performed using degenerate primers corresponding to peptide sequences of the 160kDa protein. Localization of 160kDa protein on sperm was performed using fluorescently labeled gp120, followed by inhibition experiments using antagonists to determine the specificity.
The partial cDNA sequence of the 160kDa protein demonstrated 99% identity with human macrophage mannose receptor. Sequence of testicular mannose receptor was obtained and exhibited 99% identity with that of macrophage mannose receptor. Furthermore, mannose receptor protein from sperm extract was found to have a molecular weight of 160kDa, congruent with that of 160kDa HIV-binding protein. gp120 binding and mannose receptor expression were localized to the equatorial segment in 10% of ejaculated sperm, which increased after capacitation. Mannan at molar excess concentrations completely inhibited gp120 binding to sperm.
The 160kDa, CD4-independent HIV-binding sperm protein has been identified as the human mannose receptor protein. The role of mannose receptor in HIV transmission and association with risk of sexual transmission merit further investigation.
From the Department of Biochemistry, National Institute for Research in Reproductive Health, Indian Council of Medical Research, Parel, Mumbai, Maharashtra, India.
Received for publication December 10, 2007; accepted April 4, 2008.
Supported by a grant from the Department of Biotechnology, India.
Correspondence to: Dr Atmaram H. Bandivdekar, PhD, Department of Biochemistry, National Institute for Research in Reproductive Health, Indian Council of Medical Research, Jehangir Merwanji Street, Parel, Mumbai 400 012, Maharashtra, India (e-mail: firstname.lastname@example.org).