title: Domain-specific chaperone-induced expansion is required for beta-actin folding: a comparison of beta-actin conformations upon interactions with GroEL and tail-less complex polypeptide 1 ring complex (TRiC).
abstract: Actin, an abundant cytosolic protein in eukaryotic cells, is dependent on the interaction with the chaperonin tail-less complex polypeptide 1 ring complex (TRiC) to fold to the native state. The prokaryotic chaperonin GroEL also binds non-native beta-actin, but is unable to guide beta-actin toward the native state. In this study we identify conformational rearrangements in beta-actin, by observing similarities and differences in the action of the two chaperonins. A cooperative collapse of beta-actin from the denatured state to an aggregation-prone intermediate is observed, and insoluble aggregates are formed in the absence of chaperonin. In the presence of GroEL, however, >90% of the aggregation-prone actin intermediate is kept in solution, which shows that the binding of non-native actin to GroEL is effective. The action of GroEL on bound flourescein-labeled beta-actin was characterized, and the structural rearrangement was compared to the case of the beta-actin-TRiC complex, employing the homo fluorescence resonance energy transfer methodology previously used [Villebeck, L., Persson, M., Luan, S.-L., Hammarström, P., Lindgren, M., and Jonsson, B.-H. (2007) Biochemistry 46 (17), 5083-93]. The results suggest that the actin structure is rearranged by a "binding-induced expansion" mechanism in both TRiC and GroEL, but that binding to TRiC, in addition, causes a large and specific separation of two subdomains in the beta-actin molecule, leading to a distinct expansion of its ATP-binding cleft. Moreover, the binding of ATP and GroES has less effect on the GroEL-bound beta-actin molecule than the ATP binding to TRiC, where it leads to a major compaction of the beta-actin molecule. It can be concluded that the specific and directed rearrangement of the beta-actin structure, seen in the natural beta-actin-TRiC system, is vital for guiding beta-actin to the native state.
authors.affiliation: Division of Molecular Biotechnology, IFM, Linköping University, 581 83 Linköping, Sweden.
authors.forename: Laila
authors.initials: L
authors.lastname: Villebeck
authors.forename: Satish Babu
authors.initials: SB
authors.lastname: Moparthi
authors.forename: Mikael
authors.initials: M
authors.lastname: Lindgren
authors.forename: Per
authors.initials: P
authors.lastname: Hammarström
authors.forename: Bengt-Harald
authors.initials: BH
authors.lastname: Jonsson
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018834:Chaperonin 60 / Q000378:metabolism*; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins / Q000378:metabolism*; D005454:Fluorescence Polarization; D006801:Humans; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000378:metabolism / Q000502:physiology*; D046912:Multiprotein Complexes / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary
chemical_list: D000199:Actins; D018834:Chaperonin 60; D018832:Molecular Chaperones; D046912:Multiprotein Complexes; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins