Deciphering molecular specificity in MCL-1/BAK interaction and its implications for designing potent MCL-1 inhibitors

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• The BCL-2 protein family regulates mitochondrial apoptosis.
• MCL-1, an anti-apoptotic protein, inhibits cell death by binding to BAK.
• Understanding MCL-1/BAK interaction is key for developing BH3 mimetics in cancer treatment.

Purpose of the Study:

• To elucidate the molecular mechanism of MCL-1 binding to BAK.
• To investigate the structural basis for the affinity of BAK-derived peptides to MCL-1.
• To identify key interactions influencing MCL-1/BAK complex formation and BH3 mimetic efficacy.

Main Methods:

• X-ray crystallography to determine the structures of MCL-1 bound to BAK-BH3 peptides.
• Site-directed mutagenesis to assess the role of specific amino acid residues and sub-pockets.
• Biochemical assays to measure binding affinities and inhibitor efficacy.

Main Results:

• An extended BAK-BH3 peptide shows a 65-fold higher affinity for MCL-1 compared to a canonical BH3 peptide.
• Crystal structures reveal distinct binding modes and critical hydrophobic interactions, including a π-π stacking in the p5 sub-pocket.
• Mutations in the p5 sub-pocket significantly impair MCL-1/BAK interaction and affect MCL-1 inhibitor efficacy.

Conclusions:

• The p5 hydrophobic sub-pocket of MCL-1 is crucial for high-affinity binding to BAK.
• Distinct binding specificities of BAK-BH3 peptides to MCL-1 are elucidated.
• These findings provide insights for designing novel BH3 mimetics targeting the MCL-1/BAK interaction for cancer therapy.