title: Role of small subunit in mediating assembly of red-type form I Rubisco.
abstract: Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is the key enzyme involved in photosynthetic carbon fixation, converting atmospheric CO2 to organic compounds. Form I Rubisco is a cylindrical complex composed of eight large (RbcL) subunits that are capped by four small subunits (RbcS) at the top and four at the bottom. Form I Rubiscos are phylogenetically divided into green- and red-type. Some red-type enzymes have catalytically superior properties. Thus, understanding their folding and assembly is of considerable biotechnological interest. Folding of the green-type RbcL subunits in cyanobacteria is mediated by the GroEL/ES chaperonin system, and assembly to holoenzyme requires specialized chaperones such as RbcX and RAF1. Here, we show that the red-type RbcL subunits in the proteobacterium Rhodobacter sphaeroides also fold with GroEL/ES. However, assembly proceeds in a chaperone-independent manner. We find that the C-terminal β-hairpin extension of red-type RbcS, which is absent in green-type RbcS, is critical for efficient assembly. The β-hairpins of four RbcS subunits form an eight-stranded β-barrel that protrudes into the central solvent channel of the RbcL core complex. The two β-barrels stabilize the complex through multiple interactions with the RbcL subunits. A chimeric green-type RbcS carrying the C-terminal β-hairpin renders the assembly of a cyanobacterial Rubisco independent of RbcX. Our results may facilitate the engineering of crop plants with improved growth properties expressing red-type Rubisco.
authors.affiliation: From the Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Jidnyasa
authors.initials: J
authors.lastname: Joshi
authors.affiliation: From the Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Mueller-Cajar
authors.affiliation: From the Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Yi-Chin C
authors.initials: YC
authors.lastname: Tsai
authors.affiliation: From the Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: F Ulrich
authors.initials: FU
authors.lastname: Hartl
authors.affiliation: From the Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany mhartl@biochem.mpg.de.
authors.forename: Manajit
authors.initials: M
authors.lastname: Hayer-Hartl
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D018834:Chaperonin 60 / Q000737:chemistry / Q000378:metabolism*; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics*; D017510:Protein Folding; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012274:Ribulosephosphates / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D018834:Chaperonin 60; D018832:Molecular Chaperones; C522129:RbcX protein, cyanobacteria; D012274:Ribulosephosphates; C001933:ribulose-1,5 diphosphate; D019908:Proto-Oncogene Proteins c-raf; D012273:Ribulose-Bisphosphate Carboxylase
keywords: Molecular Chaperone; Photosynthesis; Protein Assembly; Protein Folding; Ribulose-1,5-bisphosphate Carboxylase/Oxygenase (RuBisCO)