Summary auto-generated
This study describes a three-dimensional homology model of the dengue 2 virus NS3 protease (DEN2pro) based on the crystal structure of the hepatitis C virus NS3 protease. The researchers modeled the NS3 protease N-terminal 175 residues, which contain two protein domains with a chymotrypsin-like fold. Unlike HCVpro, DEN2pro lacks a zinc-binding site but likely compensates with a salt bridge between Glu93 and Lys145 for structural stability. The study identified a 12-amino acid hydrophobic region (residues 70-81) within the 40-amino acid NS2B cofactor domain as the probable main interaction site with NS3. Substrate modeling revealed that DEN2pro recognizes a different cleavage motif than HCVpro, with pair of basic residues at the P1 and P2 positions rather than cysteine or threonine. The model was validated using Profiles 3D analysis, yielding acceptable reliability scores. These structural insights into cofactor binding, substrate interactions, and protease architecture should facilitate the design and development of dengue protease inhibitors as potential antiviral therapeutics.
Key findings
- A 12-residue hydrophobic domain within NS2B (residues 70-81) likely represents the core cofactor-protease interaction site, analogous to the NS4A cofactor interaction with HCV protease
- DEN2pro lacks the zinc-binding motif present in HCVpro but probably employs a salt bridge between Glu93 and Lys145 to provide structural stability
- The dengue protease recognizes dibasic amino acids at P1 and P2 substrate positions, fundamentally different from HCVpro substrate specificity, indicating distinct P1-binding site architecture
- DEN2pro contains two domains with chymotrypsin-like fold separated by a linker region, sharing overall structural organization with HCVpro despite only 14.8% sequence identity
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Abstract
The crystal structure coordinates of the hepatitis C virus NS3 protease (HCVpro) were used to develop an homology model of the dengue 2 virus NS3 protease (DEN2pro). The amino acid sequence of DEN2pro accommodates the same alpha-helices, beta-sheets and protein-binding domains as its HCVpro counterpart, but the model predicts a number of significant differences for DEN2pro and its interactions with substrates and cofactor. Whereas HCVpro contains a Zn2+-binding site, there is no equivalent metal-binding motif in DEN2pro. It is possible that the structural role played by the zinc ion may be provided by a salt bridge between Glu93 and Lys145. The two-component viral protease comprises NS3 and a virus-encoded cofactor, NS4A for HCV and NS2B for DEN2. Previous studies have identified a central 40 amino acid cofactor domain of the dengue virus NS2B that is required for protease activity. Modelling of the putative interactions between DEN2pro and its cofactor suggests that a 12 amino acid hydrophobic region within this sequence (70-GSSPILSITISE-81) may associate directly with NS3. Modelling also suggests that the substrate binds in an extended conformation to the solvent-exposed surface of the protease, with a P1-binding site that is significantly different from its HCV counterpart. The model described in this study not only reveals unique features of the flavivirus protease but also provides a structural basis for both cofactor and substrate binding that should prove useful in the early design and development of inhibitors.