Conformational control of Bax localization and apoptotic activity by Pro168.
In healthy cells, Bax resides inactive in the cytosol because its COOH-terminal transmembrane region (TMB) is tucked into a hydrophobic pocket. During apoptosis, Bax undergoes a conformational change involving NH2-terminal exposure and translocates to mitochondria to release apoptogenic factors. How this process is regulated remains unknown. We show that the TMB of Bax is both necessary and sufficient for mitochondrial targeting. However, its availability for targeting depends on Pro168 located within the preceding loop region. Pro168 mutants of Bax lack apoptotic activity, cannot rescue the apoptosis-resistant phenotype of Bax/Bak double knockout cells, and are retained in the cytosol even in response to apoptotic stimuli. Moreover, the mutants have their NH2 termini exposed. We propose that Pro168 links the NH2 and the COOH terminus of Bax and is required for COOH-terminal release and mitochondrial targeting once this link is broken.
Schinzel
Anna
A
Institute of Molecular Medicine and Cell Research, Center for Biochemistry and Molecular Cell Research, Albert-Ludwigs-University Freiburg, Stefan-Meier Strasse 17, D-79104 Freiburg, Germany.
Kaufmann
Thomas
T
Schuler
Martin
M
Martinalbo
Jorge
J
Grubb
David
D
Borner
Christoph
C
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D002470:Cell Survival / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D011392:Proline; D011487:Protein Conformation; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000737:chemistry* / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein
C494772:BAK1 protein, human; C494826:BAX protein, human; C494773:Bak1 protein, mouse; C494827:Bax protein, mouse; D008565:Membrane Proteins; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D011392:Proline