What is the primary role of CatB and CatL proteases in the context of viral membrane fusion?

• A. They enhance viral replication in the host cell
• B. They facilitate conformational changes in proteins
• C. They degrade viral RNA during infection
• D. They prevent the entry of viruses into the host cell

Answer: (B)

The primary role of CatB (cathepsin B) and CatL (cathepsin L) proteases in the context of viral membrane fusion is to facilitate conformational changes in proteins. These proteases are cysteine proteases that are involved in the processing of viral proteins, particularly in the activation of viral glycoproteins that mediate the fusion of the viral envelope with the host cell membrane.

During the entry process of many enveloped viruses, the viral fusion proteins undergo conformational changes that are crucial for the fusion event to occur. CatB and CatL contribute to this process by cleaving specific sites on the viral proteins, which leads to the necessary conformational alterations that allow the viral membrane to fuse with the host cell membrane. This step is critical for the successful entry of the virus into the host cell, as it enables the viral genetic material to be released into the cytoplasm and begin the infection process.

The other options do not accurately describe the role of these proteases in viral membrane fusion. While CatB and CatL are involved in various cellular processes, their main contribution in the context provided revolves around facilitating the necessary conformational changes in viral proteins needed for entry into host cells.