The cleavage events that contribute to the processing of Love RA, Parge HE, Wickersham JA, Hostomsky Z, Habuka the HCV polyprotein can be grouped into three general cate-N, Moomaw EW, Adachi T, et al. The Crystal Structure of gories, each mediated by different enzymes. First, the struc-Hepatitis C Virus NS3 Proteinase Reveals a Trypsin-like Fold tural proteins located within the N-terminal third of the polyand a Structural Zinc Binding Site. Cell 1996;87:331-342. protein are cleaved from the nascent polyprotein in reactions mediated by the cellular enzyme, signalase. These reactions ABSTRACT are thus associated with the translocation of segments of the E1 and E2 proteins into the lumen of the endoplasmic During replication of hepatitis C virus (HCV), the final reticulum, and are required for the subsequent transport and steps of polyprotein processing are performed by a viral glycosylation of the envelope proteins within the endoplasmic proteinase located in the N-terminal one-third of nonreticulum and Golgi. Most of the capsid protein and the residstructural protein 3. The structure of NS3 proteinase from ual polyprotein fragment spanning the region from NS2B to HCV BK strain was determined by X-ray crystallography NS5B remain on the cytoplasmic side of the endoplasmic at 2.4 A หresolution. NS3P folds as a trypsin-like proteinase reticulum membrane. The second major type of cleavage is with two b barrels and a catalytic triad of His-57, Asp-81, represented by the NS2B/NS3 scission. This cleavage occurs Ser-139. The structure has a substrate-binding site consis-
in cis (that is, as an intramolecular reaction) and is dependent tent with the cleavage specificity of the enzyme. Novel upon polypeptide sequences on either side of the cleavage features include a structural zinc-binding site and a long site. The NS2/NS3 cleavage is zinc dependent, leading to the N-terminus that interacts with neighboring molecules by interesting conclusion that the NS2/NS3 precursor is a metalbinding to a hydrophobic surface patch.
loproteinase. 1,2 The third type of cleavage is mediated by the primary viral proteinase that is located within the N-termi-Kim JL, Morgenstern KA, Lin C, Fox T, Dwyer MD, Landro nal one third of NS3. This proteinase directs both a cis cleav-JA, Chambers SP. Crystal Structure of the Hepatitis C Virus age at the NS3/4A site, as well as trans (intermolecular reac-NS3 Protease Domain Complexed With a Synthetic NS4A tion) cleavages at each of the downstream sites (NS4A/4B, Cofactor Peptide. Cell 1996;87:343-355. NS4B/5A, NS5A/5B). 3,4 An interesting feature of these reactions is that the NS3 proteinase requires an accessory viral protein for optimal cleavage activity. This accessory factor is