Cell Surface Proteoglycans Are Necessary for A27L Protein-Mediated Cell Fusion: Identification of the N-Terminal Region of A27L Protein as the Glycosaminoglycan-Binding Domain

Abstract

We previously showed that vaccinia virus infection of BSC40 cells was blocked by soluble heparin, suggesting that cell surface heparan sulfate mediates vaccinia virus binding (C.-S. Chung, J.-C. Hsiao, Y.-S. Chang, and W. Chang, J. Virol. 72:1577–1585, 1998). In this study, we extended our previous work and demonstrated that soluble A27L protein bound to heparan sulfate on cells and interfered with vaccinia virus infection at a postbinding step. In addition, we investigated the structure of A27L protein that provides for its binding to heparan sulfate on cells. A mutant of A27L protein, named D-A27L, devoid of a cluster of 12 amino acids rich in basic residues, was constructed. In contrast to the soluble A27L protein, purified D-A27L protein was inactive in all of our assays, including binding to heparin in vitro, binding to heparan sulfate on cells, and the ability to block virus infection. These data demonstrated that the N-terminal region acts as a glycosaminoglycan (GAG)-binding domain critical for A27L protein binding to cells. Previously A27L protein was thought to be involved in fusion of virus-infected cells induced by acid treatment. When we investigated whether cell surface GAGs also participate in A27L-dependent fusion, our results indicated that soluble A27L protein blocked cell fusion, whereas D-A27L protein did not. Taken together, the results therefore demonstrated that A27L-mediated cell fusion is triggered by its interaction with cell surface GAGs through the N-terminal domain.

Vaccinia Virus Entry, Exit, and Interaction with Differentiated Human Airway Epithelia

“…However, the finding that vaccinia virus readily infected activated but not resting T cells suggested the presence of a specific cell surface viral receptor (9). In addition, recent studies found that vaccinia virus interacts with glycosaminoglycans that may be cell type specific and attached to several different receptors (8,19,31). Our data showing greater infection from the basolateral surface than at the apical surface are consistent with a previous study of MDCK epithelia (35) and support the conclusion that vaccinia virus uses a specific receptor or receptors that localize preferentially on the basolateral membrane.…”

Vaccinia Virus Motility

“…Among the several proteins on the IMV surface, three have been shown to bind to glycosoaminoglycans (GAGs). The A27L and H3L gene products bind to heparan sulfate (44,62,119) and the D8L protein binds to chondroitin sulfate (45). Virus binding to GAGs is only the initial interaction of the virus with the cell, and additional host and virus molecules are likely to be involved in virus penetration.…”

“…The A27L protein is multifunctional ( Figure 3A) and is attached to the IMV surface via interactions with proteins A17L and A14L (92,122). It is involved in IMV attachment (19), virus-cell fusion (23), cell-cell fusion (34,44,94), and wrapping of IMV to form IEV. It is also a target for IMV neutralization by Ab (93).…”

Identification of Linear Heparin-Binding Peptides Derived from Human Respiratory Syncytial Virus Fusion Glycoprotein That Inhibit Infectivity

“…Many viruses depend on cell surface GAGs to initiate infection in vitro (7,9,10,14,32,34,37,41,52,55,56,62,63). Previous work demonstrated that RSV also interacts with cell surface GAGs, as attachment and infectivity were diminished in the presence of soluble GAGs such as heparan sulfate and chondroitin sulfate B (20,26,45) or decreased by enzymatic removal of heparin-like GAGs following treatment with GAG lyases and by pretreatment of cells with chlorate to decrease cellular sulfation (26).…”