Structural basis of oligosaccharide receptor recognition by human papillomavirus - PubMed (original) (raw)
Structural basis of oligosaccharide receptor recognition by human papillomavirus
Jhimli Dasgupta et al. J Biol Chem. 2011.
Abstract
High risk human papillomavirus types 16 (HPV16) and 18 (HPV18) can cause cervical cancer. Efficient infection by HPV16 and HPV18 pseudovirions requires interactions of particles with cell-surface receptor heparan sulfate oligosaccharide. To understand the virus-receptor interactions for HPV infection, we determined the crystal structures of HPV16 and HPV18 capsids bound to the oligosaccharide receptor fragment using oligomeric heparin. The HPV-heparin structures revealed multiple binding sites for the highly negatively charged oligosaccharide fragment on the capsid surface, which is different from previously reported virus-receptor interactions in which a single type of binding pocket is present for a particular receptor. We performed structure-guided mutagenesis to generate mutant viruses, and cell binding and infectivity assays demonstrated the functional role of viral residues involved in heparin binding. These results provide a basis for understanding virus-heparan sulfate receptor interactions critical for HPV infection and for the potential development of inhibitors against HPV infection.
Figures
FIGURE 1.
Overall structures of HPV L1 capsid binding to heparin oligosaccharides. a–c, structure of the HPV16 L1 pentamer in complex with heparin fragments. d–f, structure of the HPV18 L1 pentamer in complex with heparin fragments. When the L1 capsids are drawn as surface (a, b, d, and e), the heparin molecule is drawn as a stick model. When L1 is shown in as a ribbon (c and f), the heparin oligosaccharides are shown as surface. The electrostatics of the HPV16 and HPV18 L1 capsid surface are color-coded as follows: red, negative charge; blue, positive charge; and white, neutral. The heparin binding on the L1 capsid surface appears to be asymmetric in a and d, which is attributed to different types of binding sites and also to the fact that some of the binding sites are blocked by another pentamer through crystal packing. g, sequence alignment of HPV16 L1 and HPV18 L1. Residues involved in heparin binding are marked: HPV16 (rectangles) and HPV18 (ovals). Different colors show different modes of binding. h and i, representative views of the 2_Fo_ − Fc electron density maps for two of the heparin molecules in the co-crystal structure with HPV16 and HPV18 capsids.
FIGURE 2.
Detailed interactions between the HPV16 L1 capsid with heparin. a, top view of an HPV16 pentameric L1 capsid showing surface loops involved in heparin binding in discreet color. b, binding of heparin through residues on the FG- and HI-loops. c, heparin binding through residues on the FG-, HI-, and BC-loops of two different monomers. d, heparin binding to the side wall of the L1 pentamer through residues on the EF-loop and the α4-loop on the base of the pentamer. e, heparin binding to the side wall through residues on the BC-loop and the α4-loop. In all panels, dashed lines are drawn to show charge-charge interactions or hydrogen bonds between heparin and HPV L1 residues.
FIGURE 3.
Detailed interactions between the HPV18 L1 capsid and heparin. a, heparin binding through residues on the FG- and HI-loops of two neighboring subunits. b, heparin binding through the EF-, FG-, and HI-loops. c, heparin binding to the side wall of the L1 pentamer through residues on the EF-loop and the α4-loop on the base of the pentamer. d, heparin binding to the side wall through residues on the BC- and EF-loops on the top and the α4-loop on the base of the pentamer. In all panels, dashed lines are drawn to show interactions between heparin and HPV L1 residues.
FIGURE 4.
ECM and cell binding of mutant HPV16. a, mutant virus binding to the ECM. Red, laminin 5; green, viral capsid. b, mutant virus binding to HaCaT cells. Red, actin; green, viral capsid. Projections of three confocal sections are displayed. The color of the channels was changed using Adobe Photoshop CS2 software. The five mutants are listed on the corresponding panels. The results are summarized in Table 2. ctrl, no-virus control.
FIGURE 5.
Interaction of mutant HPV16 with heparin. a, binding of WT and mutant HPV16 pseudoparticles to heparin-coated ELISA plates. b, sensitivity of WT HPV16 pseudoviral infection to high molecular weight heparin (Hep-hmw) and 10-mer heparin (Hep-10mer) (50 μg/ml final concentration). Unlike the high molecular weight heparin, which has long oligosaccharide chains, the 10-mer heparin somehow did not block the infectivity, possibly due to the inability of the short oligomer to compete with the much longer oligosaccharides on the EMC and the cell surface.
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