RESUMO
The highly divergent ribosomes of human mitochondria (mitoribosomes) synthesize 13 essential proteins of oxidative phosphorylation complexes. We have determined the structure of the intact mitoribosome to 3.5 angstrom resolution by means of single-particle electron cryogenic microscopy. It reveals 80 extensively interconnected proteins, 36 of which are specific to mitochondria, and three ribosomal RNA molecules. The head domain of the small subunit, particularly the messenger (mRNA) channel, is highly remodeled. Many intersubunit bridges are specific to the mitoribosome, which adopts conformations involving ratcheting or rolling of the small subunit that are distinct from those seen in bacteria or eukaryotes. An intrinsic guanosine triphosphatase mediates a contact between the head and central protuberance. The structure provides a reference for analysis of mutations that cause severe pathologies and for future drug design.
Assuntos
Mitocôndrias/ultraestrutura , Ribossomos/ultraestrutura , Aminoglicosídeos/farmacologia , Aminoglicosídeos/uso terapêutico , Antibacterianos/farmacologia , Cristalografia por Raios X , Farmacorresistência Bacteriana/genética , GTP Fosfo-Hidrolases/química , Doenças Genéticas Inatas/tratamento farmacológico , Doenças Genéticas Inatas/genética , Humanos , Mitocôndrias/química , RNA Mensageiro/química , RNA Ribossômico/química , Proteínas Ribossômicas/química , Ribossomos/química , Ribossomos/genéticaRESUMO
The recent rapid development of single-particle electron cryo-microscopy (cryo-EM) now allows structures to be solved by this method at resolutions close to 3â Å. Here, a number of tools to facilitate the interpretation of EM reconstructions with stereochemically reasonable all-atom models are described. The BALBES database has been repurposed as a tool for identifying protein folds from density maps. Modifications to Coot, including new Jiggle Fit and morphing tools and improved handling of nucleic acids, enhance its functionality for interpreting EM maps. REFMAC has been modified for optimal fitting of atomic models into EM maps. As external structural information can enhance the reliability of the derived atomic models, stabilize refinement and reduce overfitting, ProSMART has been extended to generate interatomic distance restraints from nucleic acid reference structures, and a new tool, LIBG, has been developed to generate nucleic acid base-pair and parallel-plane restraints. Furthermore, restraint generation has been integrated with visualization and editing in Coot, and these restraints have been applied to both real-space refinement in Coot and reciprocal-space refinement in REFMAC.
