Entry and uncoating of non-enveloped viruses: Viropexis occurs in endocytic (phagocytic) vacuoles and uncoating is facilitated primarily by which lysosomal enzyme activity?

Introduction / Context:
Many non-enveloped (naked) viruses enter cells via receptor-mediated endocytosis (viropexis). Acidification and lysosomal enzymes then promote capsid disassembly (uncoating) to release the genome.

Given Data / Assumptions:

• Viropexis occurs in endocytic vesicles.
• Question asks which enzyme class is central to uncoating.

Concept / Approach:
Lysosomal proteases degrade protein components of the capsid or trigger conformational changes that allow pore formation and genome release. DNA gyrase is a bacterial enzyme (topoisomerase II) and irrelevant to viral uncoating. Lipases target lipids, more relevant to enveloped-virus membrane changes than naked capsid breakdown.

Step-by-Step Solution:
Locate process: endosome/lysosome with decreasing pH. Identify key catalysts: proteases attacking capsid proteins. Exclude bacterial DNA gyrase and lipases as primary factors for naked capsid uncoating. Choose lysosomal protease.

Verification / Alternative check:
Inhibiting endosomal acidification or protease activity blocks uncoating for several naked viruses, confirming protease dependence.

Why Other Options Are Wrong:

• DNA gyrase: bacterial enzyme; not present in human lysosomes.
• Lysosomal lipase: targets lipids; capsid is proteinaceous.
• All of these: incorrect because only lysosomal protease is appropriate.

Common Pitfalls:
Assuming all lysosomal enzymes contribute equally; for protein capsids, proteases are the key drivers.

Final Answer:
lysosomal protease