Enzymatic Characterization of Membrane-Associated Hepatitis C Virus NS3-4A Heterocomplex Serine Protease Activity Expressed in Human Cells
Bibliographic record
Abstract
The hepatitis C virus (HCV) nonstructural (NS)3-NS4A serine protease heterocomplex is a prime target for development of novel HCV therapies, due to its essential role in maturation of the viral polyprotein. While the mode of substrate/inhibitor recognition of the HCV NS3/NS4A serine protease has been extensively studied in vitro, important molecular aspects of the mechanism of action for this membrane-bound multifunctional enzyme remain unresolved in vivo. In particular, what influence does membrane association exert on the specificity and catalysis of NS3-4A protease? To carry out this study, we developed a specific and sensitive protease assay using a unique internally quenched fluorogenic substrate (IQFS). Our IQFS enables for the first time the direct, specific detection of NS3-4A protease activity within membrane fractions isolated from human cells expressing NS3-4A and the determination of its steady-state kinetic parameters, which were found to be K(m) = 51 +/- 3 microM and k(cat) = 0.39 min(-1). We also show that our fluorescence-based bioassay can be used to evaluate specifically the potency and mode of action of NS3-4A directed inhibitors, such as in the case of a known NS3-4A substrate-analogue inhibitor (K(i) = 22 nM). Our results indicate that the membrane anchoring of NS3 by NS4A does not affect the substrate/inhibitor recognition by the NS3-4A protease domain. Further investigation may reveal whether membrane association could be important for regulating other enzymatic activities associated with NS3 (e.g., helicase and/or ATPase) and/or regulating the recently proposed cross-talk between the protease and helicase activities.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".