title: Structure of the mammalian mitochondrial ribosome reveals an expanded functional role for its component proteins.
abstract: The mitochondrial ribosome is responsible for the biosynthesis of protein components crucial to the generation of ATP in the eukaryotic cell. Because the protein:RNA ratio in the mitochondrial ribosome (approximately 69:approximately 31) is the inverse of that of its prokaryotic counterpart (approximately 33:approximately 67), it was thought that the additional and/or larger proteins of the mitochondrial ribosome must compensate for the shortened rRNAs. Here, we present a three-dimensional cryo-electron microscopic map of the mammalian mitochondrial 55S ribosome carrying a tRNA at its P site, and we find that instead, many of the proteins occupy new positions in the ribosome. Furthermore, unlike cytoplasmic ribosomes, the mitochondrial ribosome possesses intersubunit bridges composed largely of proteins; it has a gatelike structure at its mRNA entrance, perhaps involved in recruiting unique mitochondrial mRNAs; and it has a polypeptide exit tunnel that allows access to the solvent before the exit site, suggesting a unique nascent-polypeptide exit mechanism.
authors.affiliation: Division of Molecular Medicine, Wadsworth Center, New York State Department of Health, Empire State Plaza, Albany, NY 12201, USA.
authors.forename: Manjuli R
authors.initials: MR
authors.lastname: Sharma
authors.forename: Emine C
authors.initials: EC
authors.lastname: Koc
authors.forename: Partha P
authors.initials: PP
authors.lastname: Datta
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Booth
authors.forename: Linda L
authors.initials: LL
authors.lastname: Spremulli
authors.forename: Rajendra K
authors.initials: RK
authors.lastname: Agrawal
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D008928:Mitochondria / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D012333:RNA, Messenger / Q000737:chemistry / Q000378:metabolism; D012343:RNA, Transfer / Q000737:chemistry / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D001426:Bacterial Proteins; D024101:Mitochondrial Proteins; D021122:Protein Subunits; D012333:RNA, Messenger; D012343:RNA, Transfer