Mitochondrial ribosome: Difference between revisions

{{Short description|Protein complex}}

The '''mitochondrial ribosome''', or '''mitoribosome''', is a [[Protein complexes|protein complex]] that is active in [[mitochondria]] and functions as a [[Ribosomal protein|riboprotein]] for [[Translation (biology)|translating]] mitochondrial [[mRNA]]s encoded in [[mtDNA]]. The mitoribosome is attached to the [[inner mitochondrial membrane]].<ref name=":02" /> Mitoribosomes, like [[cytoplasm]]ic [[ribosome]]s, consist of two subunits — large (mt-LSU) and small (mt-SSU).<ref name="AmuntsBrown2015">{{cite journal | vauthors = Amunts A, Brown A, Toots J, Scheres SH, RamakrishnanV| title = Ribosome. The structure of the human mitochondrial ribosome | journal = Science | volume = 348 | issue = 6230 | pages = 95–98 | date = April 2015 | pmid = 25838379 | pmc = 4501431 | doi = 10.1126/science.aaa1193 }}</ref> Mitoribosomes consistof several specific proteins and fewer rRNAs.<ref name="AmuntsBrown2015"/> While mitochondrial rRNAs are encoded in the [[Mitochondrial DNA|mitochondrial genome]], the proteins that make up mitoribosomes are encoded in the [[Cell nucleus|nucleus]] and assembled by cytoplasmic ribosomes before being implanted into the mitochondria.<ref name=":3">{{cite journal | vauthors = Sylvester JE, Fischel-Ghodsian N, Mougey EB, O'Brien TW | title = Mitochondrial ribosomal proteins: candidate genes for mitochondrial disease | journal = Genetics in Medicine | volume = 6 | issue = 2 | pages = 73–80 | date = March 2003 | pmid = 15017329 | doi = 10.1097/01.GIM.0000117333.21213.17 | s2cid = 22169585 | doi-access = free }}</ref>

Mitochondria contain around 1000 proteins in [[yeast]] and 1500 proteins in [[Human|humans]]. However, only 8 and 13 proteins are encoded in [[mitochondrial DNA]] in yeast and humans respectively. Most mitochondrial proteins are synthesized via cytoplasmic ribosomes.<ref name="WenzOpaliński2015">{{cite journal | vauthors = Wenz LS, Opaliński Ł, Wiedemann N, BeckerT| title = Cooperation of protein machineries in mitochondrial protein sorting | journal = Biochimica et Biophysica Acta (BBA) - Molecular Cell Research | volume = 1853 | issue = 5 | pages = 1119–1129 | date = May 2015 | pmid = 25633533 | doi = 10.1016/j.bbamcr.2015.01.012 | doi-access = free }}</ref> Proteins that are key components in the [[electron transport chain]] are translated in mitochondria.<ref name="JohnstonWilliams2016">{{cite journal | vauthors = Johnston IG, Williams BP| title = Evolutionary Inference across Eukaryotes Identifies Specific Pressures Favoring Mitochondrial Gene Retention | journal = Cell Systems | volume = 2 | issue = 2 | pages = 101–111 | date = February 2016 | pmid = 27135164 | doi = 10.1016/j.cels.2016.01.013 | doi-access = free }}</ref><ref name="Hamers2016">{{cite journal| vauthors = HamersL|title=Why do our cell's power plants have their own DNA? |journal=Science |year=2016 |doi=10.1126/science.aaf4083 }}</ref>

[[Mammals|Mammalian]] mitoribosomes have small 28S and large 39S subunits, together forming a 55S mitoribosome.<ref name="GreberBieri2015">{{cite journal | vauthors = Greber BJ, Bieri P, Leibundgut M, Leitner A, Aebersold R, Boehringer D, BanN | title = Ribosome. The complete structure of the 55S mammalian mitochondrial ribosome | journal = Science | volume = 348 | issue = 6232 | pages = 303–308 | date = April 2015 | pmid = 25837512 | doi = 10.1126/science.aaa3872 | hdl-access = free | s2cid = 206634178 | hdl = 20.500.11850/100390 }}</ref><ref name=":0">{{cite encyclopedia | vauthors = Spremulli LL |title=The Protein Biosynthetic Machinery of Mitochondria|date=2016-01-01 |encyclopedia=Encyclopedia of Cell Biology|pages=545–554| veditors = Bradshaw RA, Stahl PD |place= Waltham |publisher= Academic Press |doi=10.1016/b978-0-12-394447-4.10066-5 |isbn=978-0-12-394796-3 }}</ref> Plant mitoribosomes have small 33S and large 50S subunits, together forming a 78S mitoribosome.<ref name="GreberBieri2015" /><ref name=":0" />

[[Animal]] mitoribosomes only have two rRNAs, 12S (SSU) and 16S (LSU), both highly minimized compared to their larger homologues.<ref name="GreberBieri2015"/> Most eukaryotoes use [[5S ribosomal RNA#Presence in organelle ribosomes|5S mitoribosomal RNA]], animals, [[Fungus|fungi]], [[Alveolate|alveolates]] and [[Euglenozoa|euglenozoans]] being the exceptions.<ref name="Valach 2014">{{cite journal | vauthors = Valach M, Burger G, Gray MW, Lang BF | title = Widespread occurrence of organelle genome-encoded 5S rRNAs including permuted molecules | journal = Nucleic Acids Research | volume = 42 | issue = 22 | pages = 13764–13777 | date = December 2014 | pmid = 25429974 | pmc = 4267664 | doi = 10.1093/nar/gku1266 }}</ref> A variety of methods have evolved to fill in the gap left by a missing 5S, with animals co-opting a Mt-tRNA (Val in vertebrates).<ref name="GreberBieri2015"/><ref>{{cite journal | vauthors = Brown A, Amunts A, Bai XC, Sugimoto Y, Edwards PC, Murshudov G, Scheres SH, Ramakrishnan V | display-authors = 6 | title = Structure of the large ribosomal subunit from human mitochondria | journal = Science | volume = 346 | issue = 6210 | pages = 718–722 | date = November 2014 | pmid = 25278503 | pmc = 4246062 | doi = 10.1126/science.1258026 | bibcode = 2014Sci...346..718B }}</ref>

== Comparison to other ribosomes ==

Like mitochondria itself is descended from bacteria, mitochondrial ribosomes are descended from bacterial ribosomes.<ref name=":02">{{cite journal | vauthors = Greber BJ, Ban N | title = Structure and Function of the Mitochondrial Ribosome | journal = Annual Review of Biochemistry | volume = 85 | issue = 1 | pages = 103–132 | date = June 2016 | pmid = 27023846 | doi = 10.1146/annurev-biochem-060815-014343 | doi-access = free }}</ref> As mitochondria evolved however, the mitoribosome has significantly diverged from its bacterial cousins leading to differences in configuration and function.<ref name=":02" /> In configuration, the mitoribosome includes additional proteins in both its large and small subunits.<ref name=":02" /> In function, mitoribosomes are much more limited in the proteins they translate, only producing a few proteins, used mostly in the mitochondrial membrane. <ref name=":02" /> Below is a table showing some properties of different ribosomes:

{| class="wikitable"

|+Properties of mitoribosomes

!

!Bacteria<ref name=":02" /><ref name=":1">{{cite journal | vauthors = De Silva D, Tu YT, Amunts A, Fontanesi F, Barrientos A | title = Mitochondrial ribosome assembly in health and disease | journal = Cell Cycle | volume = 14 | issue = 14 | pages = 2226–2250 | date = 2015-07-18 | pmid = 26030272 | pmc = 4615001 | doi = 10.1080/15384101.2015.1053672 }}</ref>

!Cytosolic (Eukaryote)<ref name=":1" /><ref name=":02" />

!Mammalian mitochondria<ref name=":02" /><ref name=":1" />

!Yeast Mitochondria<ref name=":02" /><ref name=":1" />

!Plant Mitochondria <ref>{{cite journal | vauthors = Robles P, Quesada V | title = Emerging Roles of Mitochondrial Ribosomal Proteins in Plant Development | journal = International Journal of Molecular Sciences | volume = 18 | issue = 12 | date = December 2017 | page = 2595 | pmid = 29207474 | pmc = 5751198 | doi = 10.3390/ijms18122595 | doi-access = free }}</ref>

|-

![[Sedimentation coefficient|Sedimentation Coefficient]] (LSU/SSU)

|70S (50S/30S)

|80S (60S/40S)

|55S (39S/28S)

|74S (54S/37S)

|~80S

|-

!Number of proteins (LSU/SSU)

|54 (33/21)

|79-80 (46-47/33)

|80 (50/30)

|84 (46/38)

|68-80

|-

!Number of rRNAs (LSU/SSU)

|3 (2/1)

|4 (3/1)

|3 (2/1)

|2 (1/1)

|3 (2/1)

|}

== Diseases ==

As the mitoribosome is responsible for the manufacture of proteins necessary for the [[electron transport chain]], malfunctions in the mitoribosome can result in metabolic disease.<ref name=":12">{{cite journal | vauthors = De Silva D, Tu YT, Amunts A, Fontanesi F, Barrientos A | title = Mitochondrial ribosome assembly in health and disease | journal = Cell Cycle | volume = 14 | issue = 14 | pages = 2226–2250 | date = 2015-07-18 | pmid = 26030272 | pmc = 4615001 | doi = 10.1080/15384101.2015.1053672 }}</ref> <ref name=":3" /> In humans, disease particularly manifests in energy-reliant organs such as the [[heart]], [[brain]], and [[Skeletal muscle|muscle]].<ref name=":3" /> Disease either originates from [[Mutation|mutations]] in mitochondrial rRNA or [[Gene|genes]] encoding the mitoribosomal proteins.<ref name=":3" /> In the case of mitoribosomal protein mutation, [[heredity]] of disease follows [[Mendelian inheritance]] as these proteins are encoded in the nucleus.<ref name=":12" /> On the other hand, because mitochondrial rRNA is encoded in the mitochondria, mutations in rRNA are maternally inherited.<ref name=":12" /> Examples of diseases in humans caused by these mutations include [[Leigh syndrome]], deafness, [[Neurological disorder|neurological disorders]], and various [[Cardiomyopathy|cardiomyopathies]].<ref name=":12" /> In [[Plant|plants]], mutation in mitoribosomal proteins can result in stunted size and distorted leaf growth.<ref name=":2">{{cite journal | vauthors = Robles P, Quesada V | title = Emerging Roles of Mitochondrial Ribosomal Proteins in Plant Development | journal = International Journal of Molecular Sciences | volume = 18 | issue = 12 | date = December 2017 | page = 2595 | pmid = 29207474 | pmc = 5751198 | doi = 10.3390/ijms18122595 | doi-access = free }}</ref>

== Genes ==

The mitochondrial ribosomal protein nomenclature generally follows that of bacteria, with extra numbers used for mitochondrion-specific proteins. (For more information on the nomenclature, see {{section link|Ribosomal protein|Table of ribosomal proteins}}.)

* [[MRPS1]], [[MRPS2]], [[MRPS3]], [[MRPS4]], [[MRPS5]], [[MRPS6]], [[MRPS7]], [[MRPS8]], [[MRPS9]], [[MRPS10]], [[MRPS11]], [[MRPS12]], [[MRPS13]], [[MRPS14]], [[MRPS15]], [[MRPS16]], [[MRPS17]], [[MRPS18]], [[MRPS19]], [[MRPS20]], [[MRPS21]], [[MRPS22]], [[MRPS23]], [[MRPS24]], [[MRPS25]], [[MRPS26]], [[MRPS27]], [[MRPS28]], [[MRPS29]], [[MRPS30]], [[MRPS31]], [[MRPS32]], [[MRPS33]], [[MRPS34]], [[MRPS35]]

* [[MRPL1]], [[MRPL2]], [[MRPL3]], [[MRPL4]], [[MRPL5]], [[MRPL6]], [[MRPL7]], [[MRPL8]], [[MRPL9]], [[MRPL10]], [[MRPL11]], [[MRPL12]], [[MRPL13]], [[MRPL14]], [[MRPL15]], [[MRPL16]], [[MRPL17]], [[MRPL18]], [[MRPL19]], [[MRPL20]], [[MRPL21]], [[MRPL22]], [[MRPL23]], [[MRPL24]], [[MRPL25]], [[MRPL26]], [[MRPL27]], [[MRPL28]], [[MRPL29]], [[MRPL30]], [[MRPL31]], [[MRPL32]], [[MRPL33]], [[MRPL34]], [[MRPL35]], [[MRPL36]], [[MRPL37]], [[MRPL38]], [[MRPL39]], [[MRPL40]], [[MRPL41]], [[MRPL42]]

* rRNA: [[MT-RNR1]], [[MT-RNR2]], [[MT-TV (mitochondrial)]]

== Further reading ==

* {{cite journal | vauthors = Greber BJ, Ban N | title = Structure and Function of the Mitochondrial Ribosome | journal = Annual Review of Biochemistry | volume = 85 | pages = 103–132 | date = June 2016 | pmid = 27023846 | doi = 10.1146/annurev-biochem-060815-014343 | doi-access = free }}