Poster Presentation The 44th Lorne Conference on Protein Structure and Function 2019

Structural and functional characterisation of the BCL-2 family member BCL-rambo (#126)

Kristen Scicluna 1 2 , Ahmad Wardak 1 , Richard W Birkinshaw 1 2 , Angus D Cowan 1 2 , Jason M Brouwer 1 2 , Grant Dewson 1 2 , Peter E Czabotar 1 2
  1. The Walter + Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
  2. Department of Medical Biology, University of Melbourne, Parkville, VIC, Australia

Apoptosis is a process of programmed cell suicide regulated by proteins of the BCL-2 family. Interplay between pro- and anti-apoptotic family members determines cell fate. BCL-2 family members have been the focus of extensive investigation as their dysregulation is a major driver of diseases such as cancer, nonetheless, several members remain poorly characterised. BCL-rambo is one such member sharing sequence and predicted structural homology with that of other BCL-2 family proteins. This 485-amino acid protein possesses all four BCL-2 homology (BH) domains characteristic of the BCL-2 family, a C-terminal transmembrane (TM) domain responsible for mitochondrial localisation and an atypical 250-amino acid extension (BHNo domain) that is predicted to be disordered1. The function of BCL-rambo remains ambiguous with conflicting reports suggesting both pro- and anti- apoptotic roles as well as a role in mitophagy2, the selective elimination of mitochondria. Evidence of protein:protein interactions between BCL-rambo and other BCL-2 family is lacking. As BCL-rambo expression has been implicated in glioblastoma, acute lymphoblastic leukaemia and rectal adenocarcinoma3, clarification regarding its structure and function are of great interest.

We have utilised x-ray crystallography to solve the structure of the BCL-2 fold region of BCL-rambo. The structure revealed some surprising features, in particular, a novel helix previously not observed on any other family member. In addition, complementary biochemical studies identified a potential unprecedented mode of apoptotic regulation through the apoptotic effectors BAK and BAX. These findings detail salient structural features of BCL-rambo and may elucidate a potential target within the mitochondrial apoptotic pathway for therapy.

  1. Kataoka, T. et al. Bcl-rambo, a novel Bcl-2 homologue that induces apoptosis via its unique C-terminal extension. JBC 276, 19548–19554 (2001).
  2. Nakazawa, M. et al. The human Bcl-2 family member Bcl-rambo localizes to mitochondria and induces apoptosis and morphological aberrations in Drosophila. PLoS ONE 11, e0157823 (2016).
  3. Jensen, S. A. et al. Bcl2L13 is a ceramide synthase inhibitor in glioblastoma. PNAS 111, 5682–5687 (2014).