Pro-apoptotic cleavage products of Bcl-xL form cytochrome c-conducting pores in pure lipid membranes.
During apoptotic cell death, cells usually release apoptogenic proteins such as cytochrome c from the mitochondrial intermembrane space. If Bcl-2 family proteins induce such release by increasing outer mitochondrial membrane permeability, then the pro-apoptotic, but not anti-apoptotic activity of these proteins should correlate with their permeabilization of membranes to cytochrome c. Here, we tested this hypothesis using pro-survival full-length Bcl-x(L) and pro-death Bcl-x(L) cleavage products (DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L)). Unlike Bcl-x(L), DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L) caused the release of cytochrome c from mitochondria in vivo and in vitro. Recombinant DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L), as well as Bcl-x(L), cleaved in situ by caspase 3-possessed intrinsic pore-forming activity as demonstrated by their ability to efficiently permeabilize pure lipid vesicles. Furthermore, only DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L), but not Bcl-x(L), formed pores large enough to release cytochrome c and to destabilize planar lipid bilayer membranes through reduction of pore line tension. Because Bcl-x(L) and its C-terminal cleavage products bound similarly to lipid membranes and formed oligomers of the same size, neither lipid affinity nor protein-protein interactions appear to be solely responsible for the increased membrane-perturbing activity elicited by Bcl-x(L) cleavage. Taken together, these data are consistent with the hypothesis that Bax-like proteins oligomerize to form lipid-containing pores in the outer mitochondrial membrane, thereby releasing intermembrane apoptogenic factors into the cytosol.
Basañez
G
G
Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-1855, USA. basanezg@mail.nih.gov
Zhang
J
J
Chau
B N
BN
Maksaev
G I
GI
Frolov
V A
VA
Brandt
T A
TA
Burch
J
J
Hardwick
J M
JM
Zimmerberg
J
J
D000818:Animals; D017209:Apoptosis; D002462:Cell Membrane / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism*; D003911:Dextrans / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000201:enzymology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D051020:bcl-X Protein
C494813:Bcl2l1 protein, rat; D003574:Cytochrome c Group; D003911:Dextrans; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein