Viral Adhesins (See also Chap. 161) All viral pathogens must bind to host cells, enter them, and replicate within them. Viral coat proteins serve as the ligands for cellular entry, and more than one ligand-receptor interaction may be needed; for example, HIV uses its envelope glycoprotein (gp) 120 to enter host cells by binding to both CD4 and one of two receptors for chemokines (designated CCR5 and CXCR4). Similarly, the measles virus H glycoprotein binds to both CD46 and the membrane-organizing protein moesin on host cells. The gB and gC proteins on herpes simplex virus bind to heparan sulfate; this. | Chapter 114. Molecular Mechanisms of Microbial Pathogenesis Part 3 Viral Adhesins See also Chap. 161 All viral pathogens must bind to host cells enter them and replicate within them. Viral coat proteins serve as the ligands for cellular entry and more than one ligand-receptor interaction may be needed for example HIV uses its envelope glycoprotein gp 120 to enter host cells by binding to both CD4 and one of two receptors for chemokines designated CCR5 and CXCR4 . Similarly the measles virus H glycoprotein binds to both CD46 and the membrane-organizing protein moesin on host cells. The gB and gC proteins on herpes simplex virus bind to heparan sulfate this adherence is not essential for entry but rather serves to concentrate virions close to the cell surface. This step is followed by attachment to mammalian cells mediated by the viral gD protein. Herpes simplex virus can use a number of eukaryotic cell surface receptors for entry including the herpesvirus entry mediator related to the tumor necrosis factor receptor members of the immunoglobulin superfamily two proteins called nectin-1 and nectin-2 and modified heparan sulfate. Bacterial Adhesins Among the microbial adhesins studied in greatest detail are bacterial pili and flagella Fig. 114-1 . Pili or fimbriae are commonly used by gram-negative and gram-positive bacteria for attachment to host cells and tissues. In electron micrographs these hairlike projections up to several hundred per cell may be confined to one end of the organism polar pili or distributed more evenly over the surface. An individual cell may have pili with a variety of functions. Most pili are made up of a major pilin protein subunit molecular weight 17 000-30 000 that polymerizes to form the pilus. Many strains of Escherichia coli isolated from urinary tract infections express mannose-binding type 1 pili whose binding to the integral membrane glycoproteins called uroplakins that coat the cells in the bladder epithelium is inhibited by .
