Biophysical characterization of the oligomeric state of Bax and its complex formation with Bcl-XL.

The overexpression of Bax, a member of the Bcl-2 family, promotes cell death and the dimerization (or oligomerization) of Bax has been shown to be important for its function. Using size-exclusion chromatography and in vitro cross-linking experiments, we demonstrated that Bax exists mainly as a large oligomer of approximately 30 monomeric units. Furthermore, several binding assays demonstrated that Bcl-XL, an anti-apoptotic member of the Bcl-2 family, can bind to the oligomeric form of Bax without requiring Bax to dissociate to monomers.