Ubiquitin recognition of BAP1: understanding its enzymatic function.

BRCA1-associated protein 1 (BAP1) is a nuclear localizing UCH, having tumor suppressor activity and is widely involved in many crucial cellular processes. BAP1 has garnered attention for its links with cancer, however, the molecular mechanism in the regulation of cancer by BAP1 has not been established. Amongst the four UCHs, only BAP1 and UCHL5 are able to hydrolyze small and large ubiquitin adducts but UCHL5 hydrolyzes only when it is present in the PA700 complex of the proteasome. The ability of BAP1 to cleave large ubiquitin derivatives is because of its relatively longer active-site crossover loop than other UCHs. The mechanism of ubiquitin recognition has not been studied for BAP1. The comparative enzymatic analysis of ubiquitin C-terminal hydrolase L1 (UCHL1), ubiquitin C-terminal hydrolase L3 (UCHL3), ubiquitin C-terminal hydrolase L5 (UCHL5N), and BAP1N has confirmed that enzymatically BAP1 is similar to UCHL5, which corroborates with the bioinformatics analysis done earlier. We have undertaken extensive mutational approaches to gain mechanistic insight into BAP1-ubiquitin interaction. Based on the homology-modeled BAP1 structure, we have identified a few BAP1 residues which possibly play a crucial role in ubiquitin interaction of which a few mutations have been identified in many cancers. Our comparative thermodynamic analysis reveals that BAP1-ubiquitin interaction is majorly driven by entropy factor which is unique amongst UCHs. Our study sheds light on BAP1 interaction with ubiquitin, which will be useful in understanding its enzymatic function.