Dissection of functional domains in Bcl-2 alpha by site-directed mutagenesis.
Bcl-2 alpha is a mitochondrial or perinuclear-associated oncoprotein that prolongs the life span of a variety of cell types by interfering with programmed cell death. How Bcl-2 confers cell survival is unknown, although antioxidant and antiprotease functions have been proposed. In addition, protein structures of Bcl-2 that are crucial for its survival activity are still ill-defined. Bcl-2 can occur as Bcl-2 alpha or Bcl-2 beta, two alternatively spliced forms which solely differ in their carboxyl termini. The finding that Bcl-2 alpha is active and membrane bound, but Bcl-2 beta is inactive and cytosolic, indicates that the carboxyl terminus contributes to the survival activity of Bcl-2. This region contains two subdomains, a domain X with unknown function and a hydrophobic stretch reported to mediate membrane association of Bcl-2 alpha. Recently Bcl-2-related proteins have been identified. These include Bax that heterodimerizes with Bcl-2 and, when overexpressed, counteracts Bcl-2. Bax contains two highly conserved regions of sequence homology with Bcl-2, referred to as Bcl-2 homology 1 and 2 (BH1 and BH2) domains. Site-directed mutagenesis studies have revealed that both domains are not only novel dimerization motifs for the interaction of Bax with Bcl-2 but also crucial for the survival activity of Bcl-2. Interestingly, the C-terminal end of BH2 encompasses the Bcl-2 alpha/beta splice site, as well as part of domain X in Bcl-2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)
Borner
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Institute of Biochemistry, University of Fribourg, Switzerland.
Olivier
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R
Martinou
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Mattmann
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Tschopp
J
J
Martinou
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JC
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D001483:Base Sequence; D015153:Blotting, Western; D018076:DNA, Complementary; D007739:L Cells; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D019253:Proto-Oncogene Proteins c-bcl-2; D051381:Rats
D018076:DNA, Complementary; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2