title: Heat-induced dimerization of BCL-xL through alpha-helix swapping.
abstract: The dimerization of anti-apoptotic BCL-xL by three-dimensional domain swapping has recently been discovered at alkaline pH; however, the high energetic barrier between the dimer and monomer forms of BCL-xL prevents them from interconverting at room temperature and neutral pH. Here, we demonstrate that BCL-xL dimers can be easily prepared by heating concentrated protein above 50 degrees C. The 38 kDa BCL-xL dimer was fully characterized by multi-resonance nuclear magnetic resonance (NMR) spectroscopy, and the mechanism of dimerization by alpha-helix swapping was confirmed. Dimerization strongly affects the NMR signals from the turn between helices alpha5 and alpha6 of BCL-xL and a portion of the long loop between helices alpha1 and alpha2. Measurements of residual dipolar couplings demonstrate that the solution structure of the BCL-xL dimer is very close to the crystal structure. Dimer formation does not prevent tight binding of ligands to the hydrophobic cleft of BCL-xL; however, binding of a BID BH3-peptide or a polyphenol drug, gossypol, to BCL-xL significantly slowed monomer-dimer interconversion and is an example of the control of BCL protein oligomerization by ligand binding.
authors.affiliation: Department of Biochemistry, McGill University, Montreal, Québec H3G 1Y6, Canada.
authors.forename: Alexey Yu
authors.initials: AY
authors.lastname: Denisov
authors.forename: Tara
authors.initials: T
authors.lastname: Sprules
authors.forename: James
authors.initials: J
authors.lastname: Fraser
authors.forename: Guennadi
authors.initials: G
authors.lastname: Kozlov
authors.forename: Kalle
authors.initials: K
authors.lastname: Gehring
mesh_terms: D000818:Animals; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism; D001665:Binding Sites; D003460:Crystallization; D019281:Dimerization; D006072:Gossypol / Q000737:chemistry / Q000378:metabolism; D006358:Hot Temperature; D051379:Mice; D019906:Nuclear Magnetic Resonance, Biomolecular; D051020:bcl-X Protein / Q000737:chemistry* / Q000378:metabolism
chemical_list: D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C494812:Bcl2l1 protein, mouse; D051020:bcl-X Protein; D006072:Gossypol