Impact of mutations affecting the basic cluster motif in NS5A DIII on RNA replication and virus production.

Abstract

<p>(A) Schematic representation of NS5A domains: amphipathic α-helix (AH); domain (D) I, II and III; low complexity sequences (LCS) 1 and 2. The positions of the hemagglutinin (HA) epitope tag inserted within DII and the serine cluster (SC; S452/454/457) in DIII are indicated on the top. An alignment of the amino acid sequence of the NS5A basic cluster motif of several HCV isolates belonging to genotype 1 to 7 is given at the bottom. Numbers refer to amino acid residues 352 to 355 of the JFH1 isolate (corresponding to polyprotein residues 2328 to 2331). *, invariant amino acid residue across the displayed HCV isolates;:, conservation of physicochemical properties of the amino acid. The following HCV genomes were used for the alignment (gene bank accession numbers are given in parenthesis): H77 (AF009606), Con1 (AJ238799), Ad78 (AJ132997), J6 2a (Af177036), 452 (DQ437509), ED43 (Y11604), SA13 (AF064490), 6a33 (AY859526), QC69 (EF108306) and JFH1. (B) Given glutamic acid residue substitutions were inserted into a subgenomic JFH1 Firefly luciferase reporter replicon (sgJFH1-Fluc; top panel) and replication kinetics were determined. The various sgJFH1 constructs were transfected into Huh7-Lunet cells and harvested 4, 12, 18, 24, 48 and 72 h later. Luciferase activity was quantified and values were normalized to the respective 4 h-value. Mean and SEM of three independent experiments are shown. Background was determined with an RdRp-defective mutant (GDD). (C) The same mutations were introduced into the full-length HCV chimera Jc1 [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005376#ppat.1005376.ref004" target="_blank">4</a>] shown in the top and 24, 48 and 72 h after transfection into Huh7-Lunet cells virus amounts contained in culture supernatants were quantified by limiting dilution assay. Values were normalized to the wildtype (WT) virus that was set to 100%. Mean and SEM of three independent experiments are shown. Background of the assay was determined with a deletion mutant lacking the envelope glycoprotein coding region (ΔE1E2). (D) NS5A amounts contained in cells 72 h after transfection with the Jc1 variants were determined by Western Blot with NS5A-specific antibodies; ß-actin served as loading control. Numbers in the left refer to apparent molecular weights of marker proteins in kilo Dalton (KDa).</p