Inhibition of Human Immunodeficiency Virus Type 1 Entry by a Keggin Polyoxometalate

Wang, Xiaoli; Wang, Jiao; Zhang, Wenmei; Li, Boye; Zhu, Ying; Hu, Qin; Yang, Yishu; Zhang, Xiaoguang; Yan, Hong; Zeng, Yi

The HIV-1 envelope glycoproteins, composed of gp120 and gp41, are responsible for virus binding and membrane fusion. The first step in the HIV-1 entry into the host cells involves the binding of the gp120 envelope glycoprotein to the CD4 on the target cell membrane. Previous studies revealed that POMs were effective in blocking viral absorption by interacting with the gp120 glycoprotein [41] . In our assays, PT-1 did not directly bind to gp120 in the SPR assay, however, it competed with CD4 for binding to gp120. The CD4 receptor is a monomeric protein composed of four immunoglobulin (Ig)-like extracellular domains (D1-D4). Numerous mutagenesis tests indicated that the D1 domain (complementarity-determining region (CDR2, region 21-64) is critical for gp120 binding and can be blocked by anti-CD4 antibody [42, 43] . We thus used anti-CD4 RPA-T4 antibody (binds to D1 domain) to analyze the interaction of PT-1 and CD4 on the cell membrane. The FACS analysis confirmed the direct binding of PT-1 to the D1 domain of the CD4 receptor. When gp120 interacted with CD4 and co-receptor CXCR4 or CCR5, the gp41 transmembrane subunit experiences conformational changes, and the N-terminal heptad repeats (NHR) of gp41 associate with the C-terminal heptad repeat (CHR) to form a thermostable, six-helix bundle (6-HB) core. The NHR and CHR domains are critical for the membrane fusion. NHR and CHR derived protein, such as N36 and C34, blocked gp41 core formation by interacting with CHR and NHR, respectively, and served as important targets for HIV fusion inhibitors [44] . In our study, PT-1 interfered with gp41 formation by binding to an NHR peptide. The K D value of PT-1 binding to N36 was close to the IC 50 obtained in the cell-based assay, suggesting that PT-1 inhibited HIV-1 entry by interfering with NHR and disrupting gp41 six helix bundle formation.