title: Reversible interaction of beta-actin along the channel of the TCP-1 cytoplasmic chaperonin.
abstract: The cytoplasm of eukaryotes contains a heteromeric toroidal chaperonin assembled from the t-complex TCP-1 and several other related polypeptides. The structure of the TCP-1 cytoplasmic chaperonin and that of the binary complex formed between this chaperonin and unfolded beta-actin have been studied using electron microscopy and image processing techniques. Two-dimensional averaging of front views reveals a circular stain-excluding mass surrounding a central stain-penetrating region in which the stain is excluded upon actin binding. Sections of a three-dimensional reconstruction of the chaperonin show that the inner core is an empty channel that becomes filled upon binary complex formation with unfolded beta-actin. Upon incubation with Mg-ATP, the beta-actin:chaperonin complex discharges the actin such that the chaperonin central cavity reappears. Side views from different forms of TCP-1 reveals that upon Mg-ATP binding, the cytoplasmic chaperonin undergoes a structural rearrangement that is confirmed using a new classification method.
authors.affiliation: Centro Nacional de Biotecnología, C.S.I.C., Campus Universidad Autónoma, Madrid, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Marco
authors.forename: J L
authors.initials: JL
authors.lastname: Carrascosa
authors.forename: J M
authors.initials: JM
authors.lastname: Valpuesta
mesh_terms: D000199:Actins / Q000378:metabolism / Q000648:ultrastructure*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000648:ultrastructure; D047908:Intracellular Signaling Peptides and Proteins; D008854:Microscopy, Electron / Q000379:methods; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins / Q000378:metabolism / Q000648:ultrastructure*; D011485:Protein Binding; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases; D056427:t-Complex Genome Region
chemical_list: D000199:Actins; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D000255:Adenosine Triphosphate; C116196:PPP1R11 protein, human; D044767:Ubiquitin-Protein Ligases