Binding of Hepatitis C Virus E2 Glycoprotein to CD81 Does Not Correlate with Species Permissiveness to Infection

Abstract

Hepatitis C virus (HCV) glycoprotein E2 binds to human cells by interacting with the CD81 molecule, which has been proposed to be the viral receptor. A correlation between binding to CD81 and species permissiveness to HCV infection has also been reported. We have determined the sequence of CD81 from the tamarin, a primate species known to be refractory to HCV infection. Tamarin CD81 (t-CD81) differs from the human molecule at 5 amino acid positions (155, 163, 169, 180, and 196) within the large extracellular loop (LEL), where the binding site for E2 has been located. Soluble recombinant forms of human CD81 (h-CD81), t-CD81, and African green monkey CD81 (agm-CD81) LEL molecules were analyzed by enzyme-linked immunosorbent assay for binding to E2 glycoprotein. Both h-CD81 and t-CD81 molecules were able to bind E2. Competition experiments showed that the two receptors cross-compete and that the t-CD81 binds with stronger affinity than the human molecule. Recently, h-CD81 residue 186 has been characterized as the critical residue involved in the interaction with E2. Recombinant CD81 mutant proteins were expressed to test whether human and tamarin receptors interacted with E2 in a comparable manner. Mutation of residue 186 (F186L) dramatically reduced the binding capability of t-CD81, a result that has already been demonstrated for the human receptor, whereas the opposite mutation (L186F) in agm-CD81 resulted in a neat gain of binding activity. Finally, the in vitro data were confirmed by detection of E2 binding to cotton-top tamarin (Saguinus oedipus) cell line B95-8 expressing endogenous CD81. These results indicate that the binding of E2 to CD81 is not predictive of an infection-producing interaction between HCV and host cells.Hepatitis C virus (HCV) is the major etiologic agent of non-A non-B hepatitis, infecting an estimated 400 million people worldwide (3). A striking feature of HCV infection is the tendency towards a chronic status leading to liver diseases such as chronic hepatitis, cirrhosis, and hepatocellular carcinoma (24). Moreover, HCV infection is also associated with mixed cryoglobulinemia, a B-lymphocyte proliferative disorder (2). HCV is an enveloped virus classified as a Flavivirus (20); its genome is a positive-strand RNA of 9.5 kb, containing a single open reading frame encoding a large polyprotein precursor (5, 6), whose cleavage results in mature structural and nonstructural viral proteins (18). A basic polypeptide (core) and two envelope glycoproteins (E1 and E2) are the putative HCV structural proteins (30). Because of the lack of a cell culture system for virus growth, most of the studies aimed at understanding the biological activity of viral envelope proteins have been performed on recombinant proteins (15,16,27,28). A truncated soluble recombinant form of HCV E2 glycoprotein has been reported to bind the surface of human cells (22) by interacting with the CD81 molecule (9, 19).CD81 is a member of the tetraspanin family, membrane proteins containing four transmembrane domains, a short int...

Extrahepatic disorders of HCV infection: A distinct entity of B-cell neoplasia?

“…Binding of HCV to CD81 alone is insufficient for viral infection. This is illustrated by the observation that tamarins from the Saguinus genus of New World monkeys are not susceptible to HCV infection even though tamarin CD81 binds E2 with higher affinity than human CD81 (40,41).…”

EWI-2 Is a Major CD9 and CD81 Partner and Member of a Novel Ig Protein Subfamily

“…We propose that a widely expressed partner protein such as EWI-2 could conceivably play a key role in many of these functions. Also, the CD81 large extracellular loop is clearly involved in HCV binding (37), although it may be neither necessary nor sufficient for HCV entry (82)(83)(84). Thus again, a major partner protein such as the EWI-2 molecule could possibly make an important contribution during HCV pathogenesis.…”

PGRL Is a Major CD81-Associated Protein on Lymphocytes and Distinguishes a New Family of Cell Surface Proteins

“…Despite the clear demonstration that E2 binds CD81, it seems that additional interactions between the virus and the host cell are required for fusion and viral entry (18,19). It is not known what other host cell proteins may facilitate hepatitis C virus entry.…”