title: Amyloid fibrillation of human Apaf-1 CARD.
abstract: The idea of establishing the amyloid-like fibrillation tendency of pro- and antisurvival proteins of human apoptotic pathways is relevant for delineating the conditions that lead to aberrant differentiation, development, and tissue homeostasis. As the first step in this direction, we report here that the caspase recruitment domain (CARD) of recombinant human apoptotic protease activating factor-1 (Apaf-1) can be induced to undergo amyloid-like fibrillation. The study was initiated with a set of biophysical investigations into the possibility and in vitro conditions for fibril growth. By scanning the pH-induced conformational transitions, protein stability, and stopped-flow folding-unfolding kinetics, we detected a molten globule (MG) transition of the CARD at pH <4. In a bid to reduce the surface-accessible hydrophobic patches in the MG state, the CARD monomer undergoes self-association to produce soluble oligomers that serve as precursor aggregates for protofibril formation. The monomer-to-oligomer self-association process is akin to the well-known homophilic CARD-CARD interaction by which CARDs of the same or different apoptotic proteins associate to transduce and regulate the apoptotic signal. The fibrillation reaction of the Apaf-1 CARD was conducted at pH 2.1 and 60 degrees C, because reduction of exposed hydrophobic surfaces in the MG state is more favored under the moderated solution condition. The Gaussian distributions of diameters of the fibril population suggest values of 2.1 and 2.7 nm for the mean diameter of precursor aggregates and protofibrils or elongated fibrils, respectively.
authors: School of Chemistry, University of Hyderabad, Hyderabad 500046, India.
authors: P Nageswara
authors: PN
authors: Rao
authors: K Sony
authors: KS
authors: Reddy
authors: Abani K
authors: AK
authors: Bhuyan
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism; D053477:Apoptotic Protease-Activating Factor 1 / Q000737:chemistry* / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013816:Thermodynamics
chemical_list: C506592:APAF1 protein, human; D000682:Amyloid; D053477:Apoptotic Protease-Activating Factor 1; D011994:Recombinant Proteins