Oligomeric C-terminal truncated Bax preferentially releases cytochrome c but not adenylate kinase from mitochondria, outer membrane vesicles and proteoliposomes
Mr. Wieckowski et al., Oligomeric C-terminal truncated Bax preferentially releases cytochrome c but not adenylate kinase from mitochondria, outer membrane vesicles and proteoliposomes, FEBS LETTER, 505(3), 2001, pp. 453-459
The mechanism by which the proapoptotic protein Bax releases cytochrome c f
rom mitochondria is not fully understood. The present work approaches this
problem using C-terminal truncated oligomeric Bax (Bax DeltaC). Micromolar
concentrations of Bax DeltaC released cytochrome c from isolated rat heart
and liver mitochondria, while the release of adenylate kinase was not signi
ficantly affected. Bax DeltaC also released cytochrome c but not adenylate
kinase from outer membrane vesicles filled with these proteins. However, Ba
x DeltaC was ineffective in releasing cytochrome c when outer membrane vesi
cles were obtained in the presence of glycerol, conditions under which the
number of contact sites was drastically reduced. Bax DeltaC did not liberat
e encapsulated cytochrome c and adenylate kinase from pure phospholipid ves
icles or vesicles reconstituted with porin. However, when the hexokinase-po
rin-adenine nucleotide translocase complex from brain mitochondria was reco
nstituted in vesicles, Bax DeltaC released internal cytochrome c but not ad
enylate kinase. In all these systems, only a small portion of total cytochr
ome c present in either mitochondria or vesicles could be liberated by Bax
DeltaC. Bax DeltaC also increased the accessibility of external cytochrome
c to either oxidation by complex IV or reduction by complex III in intact l
iver and heart mitochondria. Conclusions: (1) Bax DeltaC selectively releas
es cytochrome c and enables a bidirectional movement of cytochrome c across
the outer mitochondrial membrane. (2) A multiprotein complex that resemble
s the mitochondrial contact sites is a prerequisite for Bax DeltaC action.
(3) A limited pool of cytochrome c becomes the first target for Bax DeltaC.
(C) 2001 Published by Elsevier Science B.V. on behalf of the Federation of
European Biochemical Societies.