Understanding how critical tumor suppressors lose function could unlock new therapeutic approaches for aggressive cancers like mesothelioma and uveal melanoma. These malignancies frequently harbor mutations in BAP1, a protein that normally protects cells by removing ubiquitin tags and facilitating DNA repair, yet the molecular details of its dysfunction have remained elusive.
Structural analysis and mutational screening have now pinpointed three specific glutamate residues—Glu31, Glu200, and Glu201—as essential control points for BAP1's catalytic activity. Glu31 directly anchors ubiquitin substrates through a salt bridge with ubiquitin's Arg72, while Glu200 and Glu201 maintain the proper protein architecture around this binding site through the β1-β2 loop structure. Disruption of any of these residues severely compromises the enzyme's ability to cleave ubiquitin chains. The research further reveals that PARylation—the addition of poly(ADP-ribose) chains—acts as a natural brake on BAP1 activity by disrupting these crucial salt bridge interactions.
This mechanistic insight places BAP1 within a sophisticated regulatory network where its tumor suppressor function can be dynamically controlled. The salt bridge mechanism represents a relatively uncommon binding strategy among deubiquitinases, suggesting BAP1 has evolved specialized substrate recognition capabilities. For cancer therapeutics, these findings illuminate potential intervention points: compounds that stabilize the salt bridge interactions or prevent aberrant PARylation could restore BAP1 function in tumors. However, the challenge lies in developing molecules that can selectively target these specific protein-protein interactions without affecting other cellular processes. This represents foundational work toward structure-based drug design for BAP1-deficient cancers.