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Journal of Virology, October 2001, p. 9939-9946, Vol. 75, No. 20
Department of Biochemistry, Istituto di
Ricerche di Biologia Molecolare "P. Angeletti,"
Pomezia,1 and Department of
Chemistry, Università degli Studi di Salerno, Baronissi
(Salerno),2 Italy
Received 4 May 2001/Accepted 23 July 2001
The NS2-NS3 region of the hepatitis C virus polyprotein encodes a
proteolytic activity that is required for processing of the NS2/3
junction. Membrane association of NS2 and the autocatalytic nature of
the NS2/3 processing event have so far constituted hurdles to the
detailed investigation of this reaction. We now report the first
biochemical characterization of the self-processing activity of a
purified NS2/3 precursor. Using multiple sequence alignments, we were
able to define a minimal domain, devoid of membrane-anchoring
sequences, which was still capable of performing the processing
reaction. This truncated protein was efficiently expressed and
processed in Escherichia coli. The processing reaction could be significantly suppressed by growth in minimal medium in the
absence of added zinc ions, leading to the accumulation of an
unprocessed precursor protein in inclusion bodies. This protein was
purified to homogeneity, refolded, and shown to undergo processing at
the authentic NS2/NS3 cleavage site with rates comparable to those
observed using an in vitro-translated full-length NS2/3 precursor.
Size-exclusion chromatography and a dependence of the processing rate
on the concentration of truncated NS2/3 suggested a functional
multimerization of the precursor protein. However, we were unable to
observe trans cleavage activity between cleavage-site mutants and active-site mutants. Furthermore, the cleavage
reaction of the wild-type protein was not inhibited by addition of a
mutant that was unable to undergo self-processing. Site-directed
mutagenesis data and the independence of the processing rate from the
nature of the added metal ion argue in favor of NS2/3 being a cysteine protease having Cys993 and His952 as a catalytic dyad. We conclude that
a purified protein can efficiently reproduce processing at the NS2/3
site in the absence of additional cofactors.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.20.9939-9946.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Characterization of the Hepatitis C Virus NS2/3
Processing Reaction by Using a Purified Precursor
Protein
*
Corresponding author. Mailing address: Department of
Biochemistry, IRBM, Via Pontina Km 30,600, 00040 Pomezia, Italy. Phone: 39-06-91093232. Fax: 39-06-91093225. E-mail:
Christian_Steinkuhler{at}Merck.Com.
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