Jerry Adams-Projects

Jerry Adams-Projects

Projects

Determining the structure of the oligomers of Bak and Bax

The pivotal step in commitment of cells to undergo apoptosis is the formation of oligomers of Bak or Bax that permeabilise the mitochondrial outer membrane, but the structure of these oligomers remains unknown. To gain insights into their structures, we have devised a way to isolate substantial amounts of pure oligomers from mammalian cells, and are attempting to define their structures by both x-ray crystallography and cryoEM.

Clarifying how oligomeric Bak and Bax perforate the mitochondrial outer membrane

Although permeabilisation of the mitochondrial outer membrane (MOM) by oligomers of Bak and Bax is the pivotal event in apoptosis, how the topology of these proteins with respect to the MOM changes on oligomerisation has been unknown. A long-standing model is that two of their central alpha helices (a5 and a6) leave the protein core and penetrate the MOM as a hairpin. However, studies with Dr Ruth Kluck’s lab at the institute suggest instead that these helices insert only shallowly into the MOM, in-plane with it, and most likely disrupt its integrity by crowding the outer leaflet and forming proteolipidic pores (Westphal et al, in press2014).

Defining early steps in activation of Bax

In unstressed cells, Bax is mainly a cytosolic monomer with its membrane anchor (a9) tucked into a surface groove. To perform its apoptotic function, Bax must first dislodge a9, so that it can accumulate on the MOM, but the trigger for this is uncertain. It has been proposed that binding to a novel site remote from the cognate surface groove on Bax provokes extrusion of a9, but this site remains poorly defined. We hope by structural and mutagenic analysis to clarify how this site contributes to Bax activation.