title: Bcl-2 is a monomeric protein: prevention of homodimerization by structural constraints.
abstract: The pro-apoptotic activity of the Bcl-2 family member Bax has been shown to be facilitated by homodimerization. However, it is unknown whether Bcl-2 or Bcl-x(L) have to homodimerize to protect cells from apoptosis. Here we show by co-immunoprecipitation and FPLC analyses that while Bax multimerizes and forms heterodimers with Bcl-2, there is no evidence for Bcl-2 homodimerization, even in conditions under which Bcl-2 protects cells from apoptosis. Immunofluorescence studies confirmed that Bax can attract active, soluble Bcl-2 to mitochondrial membranes, but that nuclear/ER membrane-bound Bcl-2 was incapable of dislocating soluble Bcl-2. The failure of Bcl-2 to homodimerize is due to structural constraints as versions of Bcl-2 deleted or mutated in the BH1 and BH2 domains effectively dimerized with wild-type Bcl-2 and were dislocated by Bcl-2 inside cells. These data indicate that naturally occurring Bcl-2 does not expose protein domains that mediate homodimerization and therefore most likely acts as a monomer to protect cells from apoptosis.
authors.affiliation: Institute of Biochemistry, University of Fribourg, Rue du Musée 5, CH-1700 Fribourg, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Conus
authors.forename: T
authors.initials: T
authors.lastname: Kaufmann
authors.forename: I
authors.initials: I
authors.lastname: Fellay
authors.forename: I
authors.initials: I
authors.lastname: Otter
authors.forename: T
authors.initials: T
authors.lastname: Rossé
authors.forename: C
authors.initials: C
authors.lastname: Borner
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D019281:Dimerization; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D009685:Nuclear Envelope / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D012995:Solubility; D051028:bcl-2-Associated X Protein
chemical_list: C494826:BAX protein, human; C494827:Bax protein, mouse; C494828:Bax protein, rat; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D051028:bcl-2-Associated X Protein