Oligomeric C-terminal truncated Bax preferentially releases cytochrome c but not adenylate kinase from mitochondria, outer membrane vesicles and proteoliposomes.
The mechanism by which the proapoptotic protein Bax releases cytochrome c from mitochondria is not fully understood. The present work approaches this problem using C-terminal truncated oligomeric Bax (BaxDeltaC). Micromolar concentrations of BaxDeltaC released cytochrome c from isolated rat heart and liver mitochondria, while the release of adenylate kinase was not significantly affected. BaxDeltaC also released cytochrome c but not adenylate kinase from outer membrane vesicles filled with these proteins. However, BaxDeltaC was ineffective in releasing cytochrome c when outer membrane vesicles were obtained in the presence of glycerol, conditions under which the number of contact sites was drastically reduced. BaxDeltaC did not liberate encapsulated cytochrome c and adenylate kinase from pure phospholipid vesicles or vesicles reconstituted with porin. However, when the hexokinase-porin-adenine nucleotide translocase complex from brain mitochondria was reconstituted in vesicles, BaxDeltaC released internal cytochrome c but not adenylate kinase. In all these systems, only a small portion of total cytochrome c present in either mitochondria or vesicles could be liberated by BaxDeltaC. BaxDeltaC also increased the accessibility of external cytochrome c to either oxidation by complex IV or reduction by complex III in intact liver and heart mitochondria.


CONCLUSIONS
(1) BaxDeltaC selectively releases cytochrome c and enables a bidirectional movement of cytochrome c across the outer mitochondrial membrane. (2) A multiprotein complex that resembles the mitochondrial contact sites is a prerequisite for BaxDeltaC action. (3) A limited pool of cytochrome c becomes the first target for BaxDeltaC.
Wieckowski
M R
MR
Nencki Institute of Experimental Biology, Warsaw, Poland.
Vyssokikh
M
M
Dymkowska
D
D
Antonsson
B
B
Brdiczka
D
D
Wojtczak
L
L
D000263:Adenylate Kinase / Q000378:metabolism*; D000818:Animals; D001704:Biopolymers; D002462:Cell Membrane / Q000201:enzymology; D003574:Cytochrome c Group / Q000378:metabolism*; D008297:Male; D008929:Mitochondria, Heart / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000201:enzymology*; D046912:Multiprotein Complexes; D011510:Proteolipids; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D051381:Rats; D017208:Rats, Wistar; D051028:bcl-2-Associated X Protein
C494828:Bax protein, rat; D001704:Biopolymers; D003574:Cytochrome c Group; D046912:Multiprotein Complexes; D011510:Proteolipids; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; C020485:proteoliposomes; D000263:Adenylate Kinase