title: Cryo-EM structure of the large subunit of the spinach chloroplast ribosome.
abstract: Protein synthesis in the chloroplast is mediated by the chloroplast ribosome (chloro-ribosome). Overall architecture of the chloro-ribosome is considerably similar to the Escherichia coli (E. coli) ribosome but certain differences are evident. The chloro-ribosome proteins are generally larger because of the presence of chloroplast-specific extensions in their N- and C-termini. The chloro-ribosome harbours six plastid-specific ribosomal proteins (PSRPs); four in the small subunit and two in the large subunit. Deletions and insertions occur throughout the rRNA sequence of the chloro-ribosome (except for the conserved peptidyl transferase center region) but the overall length of the rRNAs do not change significantly, compared to the E. coli. Although, recent advancements in cryo-electron microscopy (cryo-EM) have provided detailed high-resolution structures of ribosomes from many different sources, a high-resolution structure of the chloro-ribosome is still lacking. Here, we present a cryo-EM structure of the large subunit of the chloro-ribosome from spinach (Spinacia oleracea) at an average resolution of 3.5 Å. High-resolution map enabled us to localize and model chloro-ribosome proteins, chloroplast-specific protein extensions, two PSRPs (PSRP5 and 6) and three rRNA molecules present in the chloro-ribosome. Although comparable to E. coli, the polypeptide tunnel and the tunnel exit site show chloroplast-specific features.
authors.affiliation: School of Biological Sciences, Nanyang Technological University, Singapore.
authors.forename: Tofayel
authors.initials: T
authors.lastname: Ahmed
authors.affiliation: School of Biological Sciences, Nanyang Technological University, Singapore.
authors.forename: Zhan
authors.initials: Z
authors.lastname: Yin
authors.affiliation: School of Biological Sciences, Nanyang Technological University, Singapore.|NTU Institute of Structural Biology, Nanyang Technological University, Singapore.
authors.forename: Shashi
authors.initials: S
authors.lastname: Bhushan
mesh_terms: D002736:Chloroplasts / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy; D054658:Ribosome Subunits, Large / Q000648:ultrastructure*; D018724:Spinacia oleracea / Q000648:ultrastructure*