Date of Award
Mitochondrial outer membrane permeabilization (MOMP) by Bax oligomerization triggers apoptosis. BCl-2 family proteins, classified as BH3 only proteins, pro-survival proteins, or pro-apoptotic proteins, control apoptosis partly through their agonist or antagonistic effects on Bax, which are mediated by their conserved BH3 domains. All BH3 domains form an alpha helix containing 5-7 conserved hydrophobic residues, designated H0-H5, and one conserved aspartic acid that drive interaction with Bax and other ‘multi-domain’ BCl-2 members. BH3 agonists induce Bax oligomerization, while BH3 antagonists sequester Bax to prevent MOMP. We discovered that voltage dependent anion channels (VDACs) in the MOM contain a putative BH3-like domain based on sequence similarity with known BH3 domains. This study tested the hypothesis that the VDAC2 isoform contains a functional BH3 domain that binds recombinant Bax in a manner similar to the Bim BH3 domain. Using fluorescent-tagged synthetic peptides, Bax bound VDAC2, but with a 4-fold lower affinity than the Bim BH3 domain. The conserved aspartate was important for this interaction, as substitution with arginine at this position reduced Bax affinity by 2.6-fold. A proline at the H0 position also promoted Bax binding to VDAC2. All known BH3 domains have a conserved leucine at the H2 position, but this is shifted one residue closer to H1 in VDAC2. Substitution of leucine for a smaller hydrophobic alanine at H2 substantially lowered the KD, suggesting the non-conserved position of the H2 Leu contributed to Bax’s lower affinity for VDAC2, along with the large aromatic residues at H1 (Tyr), H4 (Phe), and H5 (Phe). The N-terminus of VDAC2 thus has the essential elements of a BH3 domain, but the combination of residues at the conserved positions make it less well suited for binding to Bax.
Ferkany, Lillian, "Does VDAC2 Have A BH3 Domain?" (2023). Honors Theses. 2880.