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J. Virol., 10 1996, 6694-6700, Vol 70, No. 10
C Steinkuhler, A Urbani, L Tomei, G Biasiol, M Sardana, E Bianchi, A Pessi and R De Francesco
The protease domain of the hepatitis C virus (HCV) protein NS3 was
expressed in Escherichia coli, purified to homogeneity, and shown to be
active on peptides derived from the sequence of the NS4A-NS4B junction.
Experiments were carried out to optimize protease activity. Buffer
requirements included the presence of detergent, glycerol, and
dithiothreitol, pH between 7.5 and 8.5, and low ionic strength. C- and
N-terminal deletion experiments defined a peptide spanning from the P6 to
the P4' residue as a suitable substrate. Cleavage kinetics were
subsequently measured by using decamer P6-P4' peptides corresponding to all
intermolecular cleavage sites of the HCV polyprotein. The following order
of cleavage efficiency, in terms of kcat/Km, was determined: NS5A- NS5B
> NS4A-NS4B >> NS4B-NS5A. A 14-mer peptide containing residues 21
to 34 of the protease cofactor NS4A (Pep4A 21-34), when added in
stoichiometric amounts, was shown to increase cleavage rates of all
peptides, the largest effect (100-fold) being observed on the hydrolysis of
the NS4B-NS5A decamer. From the kinetic analysis of cleavage data, we
conclude that (i) primary structure is an important determinant of the
efficiency with which each site is cleaved during polyprotein processing,
(ii) slow cleavage of the NS4B-NS5A site in the absence of NS4A is due to
low binding affinity of the enzyme for this site, and (iii) formation of a
1:1 complex between the protease and Pep4A 21-34 is sufficient and required
for maximum activation.
Copyright © 1996, American Society for Microbiology
Activity of purified hepatitis C virus protease NS3 on peptide substrates
Istituto di Ricerche di Biologia Molecolare P. Angeletti Pomezia, Rome, Italy.
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