Mitochondrial ribosome

Mitochondria contain around 1000 proteins in yeast and 1500 proteins in 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.[4] Proteins that are key components in the electron transport chain are translated in mitochondria.[5][6]

Mammalian mitoribosomes have small 28S and large 39S subunits, together forming a 55S mitoribosome.[7][8] Plant mitoribosomes have small 33S and large 50S subunits, together forming a 78S mitoribosome.[7][8]

Animal mitoribosomes only have two rRNAs, 12S (SSU) and 16S (LSU), both highly minimized compared to their larger homologues.[7] Most eukaryotoes use 5S mitoribosomal RNA, animals, fungi, alveolates and euglenozoans being the exceptions.[9] 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).[7][10]

Like mitochondria itself is descended from bacteria, mitochondrial ribosomes are descended from bacterial ribosomes.[1] As mitochondria evolved however, the mitoribosome has significantly diverged from its bacterial cousins leading to differences in configuration and function.[1] In configuration, the mitoribosome includes additional proteins in both its large and small subunits.[1] In function, mitoribosomes are much more limited in the proteins they translate, only producing a few proteins, used mostly in the mitochondrial membrane. [1] Below is a table showing some properties of different ribosomes:

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.[13] [3] In humans, disease particularly manifests in energy-reliant organs such as the heart, brain, and muscle.[3] Disease either originates from mutations in mitochondrial rRNA or genes encoding the mitoribosomal proteins.[3] In the case of mitoribosomal protein mutation, heredity of disease follows Mendelian inheritance as these proteins are encoded in the nucleus.[13] On the other hand, because mitochondrial rRNA is encoded in the mitochondria, mutations in rRNA are maternally inherited.[13] Examples of diseases in humans caused by these mutations include Leigh syndrome, deafness, neurological disorders, and various cardiomyopathies.[13] In plants, mutation in mitoribosomal proteins can result in stunted size and distorted leaf growth.[14]

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 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)

• Greber BJ, Ban N (June 2016). "Structure and Function of the Mitochondrial Ribosome". Annual Review of Biochemistry. 85: 103–132. doi:10.1146/annurev-biochem-060815-014343. PMID 27023846.