Identification of substrates of the CRL4-HBx E3 ubiquitin ligase

Hepatitis B Virus (HBV) remains a major public health problem, and is a major cause liver cancer worldwide. HBV infection in vivo requires the function of the HBx protein, which facilitates expression of viral genes from the episomal genome by an unknown mechanism. Evidence suggests that HBx functions as a targeting subunit for the CRL4 E3 ubiquitin ligase, redirecting the complex to target and degrade an unknown host restriction factor. We used substrate trapping proteomics to search for ubiquitylation substrates of HBx. We used MLN4924 to block CRL activity and stabilize interactions between HBx and its substrates. We then performed APMS to identify bound proteins and potential substrates.