Hepatitis C virus nonstructural protein 4B: a journey into unexplored territory

Abstract

Hepatitis C virus (HCV) is a positive-strand RNA virus that replicates its genome in a membrane-associated replication complex. Nonstructural protein 4B (NS4B) induces the specific membrane alteration, designated as membranous web (MW), that harbours this complex. HCV NS4B is an integral membrane protein predicted to comprise four transmembrane segments in its central part. The N-terminal part comprises two amphipathic alpha-helices of which the second has the potential to traverse the membrane bilayer, likely upon oligomerisation. The C-terminal part comprises a predicted highly conserved alpha-helix, a membrane-associated amphipathic alpha-helix and two reported palmitoylation sites. NS4B interacts with other viral nonstructural proteins and has been reported to bind viral RNA. In addition, it was found to harbour an NTPase activity. Finally, NS4B has recently been found to have a role in viral assembly. Much work needs to be done with respect to further dissecting these multiple functions as well as providing a refined membrane topology and complete structure of NS4B. Progress in this direction should yield important insights into the functional architecture of the HCV replication complex and may reveal new opportunities for antiviral intervention against a leading cause of chronic hepatitis, liver cirrhosis and hepatocellular carcinoma worldwide.

Hepatitis c virus and host cell lipids: An intimate connection

“…52 However, the importance of these properties of NS4B for the viral replication cycle is still not clear. 53 NS5A, a master regulator of HCV replication and assembly, is a dimeric zinc-binding metalloprotein. 54 It is composed of four domains: 55 an N-terminal AH essential for attachment to cellular membranes and contributing to LD targeting; 56,57 an RNA binding domain (D1); an intrinsically unfolded and poorly conserved D2 contributing to RNA replication; 58 and a C-terminally located D3, crucial for virus assembly (D3).…”

Hepatitis C Virus Is Released via a Noncanonical Secretory Route

“…This encodes a polyprotein which is posttranslationally cleaved into six nonstructural (NS) proteins, the ion channel p7 protein, and the structural proteins Core, E1, and E2 (1). The NS proteins reside at the outer leaflet of the endoplasmic reticulum (ER) membrane where NS4B and NS5A in particular induce membrane alterations resulting in the formation of the membranous web, which is the major site for HCV replication (2)(3)(4)(5). Core is targeted to adjacent lipid droplets (LDs) (6,7), which represent intracellular lipid deposits and are considered important for production of infectious particles (1,7,8).…”

Analysis of Immumoreactivity of Heterologously Expressed Non-structural Protein 4B (NS4B) from Hepatitis C Virus (HCV) Genotype 1a

“…NS4B is amongthe HCV major immunogenic proteins and it is widely used in anti-HCV antibody detection in diagnostic serologic tests (6)(7)(8). Furthermore, since NS4B is a key protein in virus life cycle, it provides new opportunities for antiviral intervention against a leading cause of liver diseases worldwide (12). Therefore, rapid, high yield, and economical production of recombinant HCV NS4B is essential for producing HCV diagnostic kits.…”