title: Coupled chaperone action in folding and assembly of hexadecameric Rubisco.
abstract: Form I Rubisco (ribulose 1,5-bisphosphate carboxylase/oxygenase), a complex of eight large (RbcL) and eight small (RbcS) subunits, catalyses the fixation of atmospheric CO(2) in photosynthesis. The limited catalytic efficiency of Rubisco has sparked extensive efforts to re-engineer the enzyme with the goal of enhancing agricultural productivity. To facilitate such efforts we analysed the formation of cyanobacterial form I Rubisco by in vitro reconstitution and cryo-electron microscopy. We show that RbcL subunit folding by the GroEL/GroES chaperonin is tightly coupled with assembly mediated by the chaperone RbcX(2). RbcL monomers remain partially unstable and retain high affinity for GroEL until captured by RbcX(2). As revealed by the structure of a RbcL(8)-(RbcX(2))(8) assembly intermediate, RbcX(2) acts as a molecular staple in stabilizing the RbcL subunits as dimers and facilitates RbcL(8) core assembly. Finally, addition of RbcS results in RbcX(2) release and holoenzyme formation. Specific assembly chaperones may be required more generally in the formation of complex oligomeric structures when folding is closely coupled to assembly.
authors.affiliation: Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
authors.forename: Cuimin
authors.initials: C
authors.lastname: Liu
authors.forename: Anna L
authors.initials: AL
authors.lastname: Young
authors.forename: Amanda
authors.initials: A
authors.lastname: Starling-Windhof
authors.forename: Andreas
authors.initials: A
authors.lastname: Bracher
authors.forename: Sandra
authors.initials: S
authors.lastname: Saschenbrecker
authors.forename: Bharathi Vasudeva
authors.initials: BV
authors.lastname: Rao
authors.forename: Karnam Vasudeva
authors.initials: KV
authors.lastname: Rao
authors.forename: Otto
authors.initials: O
authors.lastname: Berninghausen
authors.forename: Thorsten
authors.initials: T
authors.lastname: Mielke
authors.forename: F Ulrich
authors.initials: FU
authors.lastname: Hartl
authors.forename: Roland
authors.initials: R
authors.lastname: Beckmann
authors.forename: Manajit
authors.initials: M
authors.lastname: Hayer-Hartl
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D018835:Chaperonin 10 / Q000378:metabolism; D018834:Chaperonin 60 / Q000378:metabolism; D020285:Cryoelectron Microscopy; D020035:Holoenzymes / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012273:Ribulose-Bisphosphate Carboxylase / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D046940:Synechococcus / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D018835:Chaperonin 10; D018834:Chaperonin 60; D020035:Holoenzymes; D018832:Molecular Chaperones; C522129:RbcX protein, cyanobacteria; D012273:Ribulose-Bisphosphate Carboxylase