Free thiol groups are essential for infectivity of human cytomegalovirus

This study investigates the role of free thiol groups in human cytomegalovirus (CMV) infectivity. Researchers treated CMV with DTNB, a membrane-impermeable thiol-blocking reagent, and found that it completely abolished viral infectivity in a dose-dependent manner, though the virus retained its ability to bind to host cells. Remarkably, when DTNB-inactivated CMV was treated with dithiothreitol (DTT), a disulfide-reducing agent, approximately 65% of infectivity was recovered. These findings demonstrate that free accessible thiol groups on CMV surface proteins are essential for the infection process, likely participating in disulfide bond formation or interchange during viral entry. In contrast, HSV-1 infectivity was unaffected by DTNB treatment, suggesting that CMV uniquely exposes critical thiol groups. The results indicate that DTNB-blocked thiol groups prevent post-attachment events required for successful infection, while the virus-receptor attachment itself remains intact. The authors propose that thiol-disulfide interchange may be critical for CMV entry and fusion, potentially involving viral glycoproteins gB and gH.

Key findings

• DTNB treatment completely blocks CMV infectivity in a dose-dependent manner, with maximal effect at 250 µM and rapid inactivation within 30-45 minutes
• DTNB-inactivated CMV retains 70% binding capacity to host cells, indicating the virus can attach normally but cannot complete infection
• DTT treatment restores approximately 65% of CMV infectivity lost through DTNB blocking, demonstrating that viral infectivity depends on accessible free thiol groups
• HSV-1 infectivity is unaffected by DTNB treatment, indicating CMV uniquely exposes critical thiol groups essential for entry
• Free thiol groups on CMV likely participate in disulfide bond formation or interchange required for post-attachment entry events