Poster Presentation The 47th Lorne Conference on Protein Structure and Function 2022

Key role for the α1-α2 loop in restraining BAK activation identified from the structure of BAK bound to activating antibody 7D10 (#218)

Michelle S Miller 1 , Adeline Y Robin 1 , Sweta Iyer 1 , Melissa X Shi 1 , Ahmad Z Wardak 1 , Daisy Lio 1 , Nicholas A Smith 2 , Brian J Smith 2 , Richard W Birkinshaw 1 , Peter E Czabotar 1 , Ruth M Kluck 1 , Peter M Colman 1
  1. Walter and Eliza Hall Institute, Parkville, VIC, Australia
  2. Department of Chemistry and Physics, La Trobe Institute for Molecular Sciences, Bundoora, Victoria, Australia

BAK is a key effector of apoptosis that is activated by BH3-only proteins to permeabilise the outer mitochondrial membrane and release apoptotic effector proteins into the cytosol. We have previously reported the discovery of antibody 7D10 which can activate BAK on mitochondria through binding to an epitope located in the loop connecting helices α1 and α2. Here we report the crystal structure of the complex between 7D10 and the BAK mutant L100A. The crystal structure provided insights into the mechanism by which 7D10 activates BAK and revealed a regulatory role for the α1-α2 loop, and particularly for residue Met60. Mutating Met60 to alanine or glycine results in reduced protein stability and elevated sensitivity to activation by BID, illustrating the importance of Met60 as a linchpin stabilising the inert, monomeric structure of BAK.