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J. Virol., Jan 1995, 198-205, Vol 69, No. 1
R Bartenschlager, L Ahlborn-Laake, K Yasargil, J Mous and H Jacobsen
Processing of the hepatitis C virus polyprotein is accomplished by a series
of cotranslational and posttranslational cleavages mediated by host cell
signalases and two virally encoded proteinases. Of these the NS3 proteinase
is essential for processing at the NS3/4A, NS4A/4B, NS4B/5A, and NS5A/5B
junctions. Processing between NS3 and NS4A occurs in cis, implying an
intramolecular reaction mechanism, whereas cleavage at the other sites can
also be mediated in trans. Sequence analysis of the amino termini of mature
cleavage products and comparisons of amino acid residues around the
scissile bonds of various hepatitis C virus isolates identified amino acid
residues which might contribute to substrate specificity and processing
efficiency: an acidic amino acid at the P6 position, a Thr or Cys at the P1
position, and a Ser or Ala at the P1' position. To study the importance of
these residues for NS3- mediated cleavage we have undertaken a mutational
analysis using an NS3'-5B polyprotein expressed by recombinant vaccinia
viruses in mammalian cells. For all NS3-dependent cleavage sites P1
substitutions had the most drastic effects on cleavage efficiency, showing
that amino acid residues at this position are the most critical substrate
determinants. Since less drastic effects were found for substitutions at
the P1' position, these residues appear to be less important for proper
cleavage. For all cleavage sites the P6 acidic residue was dispensable,
suggesting that it is not essential for substrate recognition and
subsequent cleavage. Analysis of a series of mutations at the NS3/4A site
revealed great flexibility for substitutions compared with more stringent
requirements at the trans cleavage sites. On the basis of these results we
propose a model in which processing in cis is determined primarily by
polyprotein folding, whereas cleavage in trans is governed not only by the
structure of the polyprotein but also by specific interactions between the
proteinase and the polyprotein substrate at or around the scissile bond.
Copyright © 1995, American Society for Microbiology
Substrate determinants for cleavage in cis and in trans by the hepatitis C virus NS3 proteinase
Institute for Virology, Johannes-Gutenberg-University of Mainz, Germany.
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