Phylogenetic analysis of the MCL1 BH3 binding groove and rBH3 sequence motifs in the p53 and INK4 protein families

Abstract

B-cell lymphoma 2 (Bcl-2) proteins are central, conserved regulators of apoptosis. Bcl-2 family function is regulated by binding interactions between the Bcl-2 homology 3 (BH3) motif in pro-apoptotic family members and the BH3 binding groove found in both the pro-apoptotic effector and anti-apoptotic Bcl-2 family members. A novel motif, the reverse BH3 (rBH3), has been shown to interact with the anti-apoptotic Bcl-2 homolog MCL1 (Myeloid cell leukemia 1) and have been identified in the p53 homolog p73, and the CDK4/6 (cyclin dependent kinase 4/6) inhibitor p18INK4c, (p18, cyclin-dependent kinase 4 inhibitor c). To determine the conservation of rBH3 motif, we first assessed conservation of MCL1's BH3 binding groove, where the motif binds. We then constructed neighbor-joining phylogenetic trees of the INK4 and p53 protein families and analyzed sequence conservation using sequence logos of the rBH3 locus. This showed the rBH3 motif is conserved throughout jawed vertebrates p63 and p73 sequences and in chondrichthyans, amphibians, mammals, and some reptiles in p18. Finally, a potential rBH3 motif was identified in mammalian and osteichthyan p19INK4d (p19, cyclin dependent kinase 4 inhibitor d). These findings demonstrate that the interaction between MCL1 and other cellular proteins mediated by the rBH3 motif may be conserved throughout jawed vertebrates.

Polypyrimidine tract binding protein 1 (PTBP1) contains a novel regulatory sequence, the rBH3, that binds the prosurvival protein MCL1

“…The MCL1 binding pocket, into which the rBH3 of RRM1 binds, serves as the interface at which decisions regarding cell survival occur, as its canonical function is inhibiting apoptosis via binding and sequestering BH3 helices of proapoptotic Bcl-2 family proteins ( 38 ). We have recently shown that the MCL1 BH3-binding groove is conserved among all vertebrate classes, underscoring the evolutionary importance of this biological interface ( 55 ). Until recently, this apoptotic interface has historically been described as a terminal interaction within the apoptotic pathway, with no feed out to other cellular processes.…”