MT-ND3 is a
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
of the
mitochondrial genome
Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
coding for the NADH dehydrogenase 3 (ND3) protein.
The ND3 protein is a subunit of
NADH dehydrogenase (ubiquinone)
Respiratory complex I, (also known as NADH:ubiquinone oxidoreductase, Type I NADH dehydrogenase and mitochondrial complex I) is the first large protein complex of the respiratory chains of many organisms from bacteria to humans. It catalyzes the ...
, which is located in the
mitochondrial inner membrane
The inner mitochondrial membrane (IMM) is the mitochondrial membrane which separates the mitochondrial matrix from the intermembrane space.
Structure
The structure of the inner mitochondrial membrane is extensively folded and compartmentalized. ...
and is the largest of the five complexes of the
electron transport chain
An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...
.
Variants of MT-ND3 are associated with
(MELAS),
Leigh's syndrome
Leigh syndrome (also called Leigh disease and subacute necrotizing encephalomyelopathy) is an inherited neurometabolic disorder that affects the central nervous system. It is named after Archibald Denis Leigh, a British neuropsychiatrist who fir ...
(LS) and
Leber's hereditary optic neuropathy
Leber's hereditary optic neuropathy (LHON) is a mitochondrially inherited (transmitted from mother to offspring) degeneration of retinal ganglion cells (RGCs) and their axons that leads to an acute or subacute loss of central vision; it predomin ...
(LHON).
Structure
General features
MT-ND3 is located in human
mitochondrial DNA
Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
from base pair 10,059 to 10,404.
The MT-ND3 gene produces a 13 kDa protein composed of 115 amino acids.
MT-ND3 is one of seven mitochondrial genes encoding subunits of the enzyme
NADH dehydrogenase (ubiquinone)
Respiratory complex I, (also known as NADH:ubiquinone oxidoreductase, Type I NADH dehydrogenase and mitochondrial complex I) is the first large protein complex of the respiratory chains of many organisms from bacteria to humans. It catalyzes the ...
, together with
MT-ND1
MT-ND1 is a gene of the mitochondrial genome coding for the NADH-ubiquinone oxidoreductase chain 1 (ND1) protein. The ND1 protein is a subunit of NADH dehydrogenase, which is located in the mitochondrial inner membrane and is the largest of the ...
,
MT-ND2
MT-ND2 is a gene of the mitochondrial genome coding for the NADH dehydrogenase 2 (ND2) protein. The ND2 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the largest of the five ...
,
MT-ND4
MT-ND4 is a gene of the mitochondrial genome coding for the NADH-ubiquinone oxidoreductase chain 4 (ND4) protein. The ND4 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the l ...
,
MT-ND4L
MT-ND4L is a gene of the mitochondrial genome coding for the NADH-ubiquinone oxidoreductase chain 4L (ND4L) protein. The ND4L protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is th ...
,
MT-ND5
MT-ND5 is a gene of the mitochondrial genome coding for the NADH-ubiquinone oxidoreductase chain 5 protein (ND5). The ND5 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the la ...
, and
MT-ND6
MT-ND6 is a gene of the mitochondrial genome coding for the NADH-ubiquinone oxidoreductase chain 6 protein (ND6). The ND6 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the la ...
. Also known as
Complex I
Respiratory complex I, (also known as NADH:ubiquinone oxidoreductase, Type I NADH dehydrogenase and mitochondrial complex I) is the first large protein complex of the Electron transport chain, respiratory chains of many organisms from bacteria to ...
, this enzyme is the largest of the respiratory complexes. The structure is L-shaped with a long,
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, th ...
transmembrane
A transmembrane protein (TP) is a type of integral membrane protein that spans the entirety of the cell membrane. Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane. They frequentl ...
domain and a
hydrophilic
A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press.
In contrast, hydrophobes are no ...
domain for the peripheral arm that includes all the known redox centres and the NADH binding site. The MT-ND3 product and the rest of the mitochondrially encoded subunits are the most hydrophobic of the subunits of Complex I and form the core of the transmembrane region.
Untranslated extra nucleotide
In the MT-ND3 gene from many species of birds and turtles there is an extra nucleotide that is not translated to protein.
Translational frameshifting or
RNA editing
RNA editing (also RNA modification) is a molecular process through which some cells can make discrete changes to specific nucleotide sequences within an RNA molecule after it has been generated by RNA polymerase. It occurs in all living organisms ...
are alternative explanations for maintenance of the functionality of the ND3 reading frame in birds possessing the one-nucleotide insertion.
This extra nucleotide feature suggests that turtles might be related to
Archosauria, as evidenced by
molecular phylogeny
Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
studies. The absence of the extra nucleotide in crocodilians and some birds and turtles might also indicate that the corresponding taxa have lost this feature.
Function
The MT-ND3 product is a subunit of the respiratory chain
Complex I
Respiratory complex I, (also known as NADH:ubiquinone oxidoreductase, Type I NADH dehydrogenase and mitochondrial complex I) is the first large protein complex of the Electron transport chain, respiratory chains of many organisms from bacteria to ...
that is believed to belong to the minimal assembly of core proteins required to catalyze
NADH
Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an aden ...
dehydrogenation and
electron transfer
Electron transfer (ET) occurs when an electron relocates from an atom or molecule to another such chemical entity. ET is a mechanistic description of certain kinds of redox reactions involving transfer of electrons.
Electrochemical processes ar ...
to
ubiquinone
Coenzyme Q, also known as ubiquinone and marketed as CoQ10, is a coenzyme family that is ubiquitous in animals and most bacteria (hence the name ubiquinone). In humans, the most common form is coenzyme Q10 or ubiquinone-10.
It is a 1,4-benzoq ...
(coenzyme Q10). Initially,
NADH
Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an aden ...
binds to Complex I and transfers two electrons to the
isoalloxazine ring
Flavins (from Latin ''flavus'', "yellow") are organic compounds, like their base, pteridine. They are formed by the tricyclic heterocycle isoalloxazine. The biochemical source is the vitamin riboflavin. The flavin moiety is often attached with a ...
of the
flavin mononucleotide
Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, is a biomolecule produced from riboflavin (vitamin B2) by the enzyme riboflavin kinase and functions as the prosthetic group of various oxidoreductases, including NADH dehydrogenase, as ...
(FMN) prosthetic arm to form FMNH
2. The electrons are transferred through a series of
iron-sulfur (Fe-S) clusters in the prosthetic arm and finally to coenzyme Q10 (CoQ), which is reduced to
ubiquinol
A ubiquinol is an electron-rich (reduced) form of coenzyme Q (ubiquinone). The term most often refers to ubiquinol-10, with a 10-unit tail most commonly found in humans.
The natural ubiquinol form of coenzyme Q is 2,3-dimethoxy-5-methyl-6-poly p ...
(CoQH
2). The flow of electrons changes the redox state of the protein, resulting in a conformational change and p''K'' shift of the ionizable side chain, which pumps four hydrogen ions out of the mitochondrial matrix.
[
]
Clinical significance
Pathogenic variants of the mitochondrial gene MT-ND3 are known to cause mtDNA-associated Leigh syndrome
Leigh syndrome (also called Leigh disease and subacute necrotizing encephalomyelopathy) is an inherited neurometabolic disorder that affects the central nervous system. It is named after Archibald Denis Leigh, a British neuropsychiatrist who fir ...
, as are variants of MT-ATP6
''MT-ATP6'' (or ''ATP6'') is a mitochondrial gene with the full name 'mitochondrially encoded ATP synthase membrane subunit 6' that encodes the ATP synthase Fo subunit 6 (or subunit/chain A). This subunit belongs to the Fo complex of the large, ...
, MT-TL1
Mitochondrially encoded tRNA leucine 1 (UUA/G) also known as MT-TL1 is a transfer RNA which in humans is encoded by the mitochondrion, mitochondrial ''MT-TL1'' gene.
Structure
The ''MT-TL1'' gene is located on the Locus (genetics), p arm of the ...
, MT-TK
Mitochondrially encoded tRNA lysine also known as MT-TK is a transfer RNA which in humans is encoded by the mitochondrion, mitochondrial ''MT-TK'' gene.
Structure
The ''MT-TK'' gene is located on the Locus (genetics), p arm of the mitochondrial ...
, MT-TW
Mitochondrially encoded tRNA tryptophan also known as MT-TW is a transfer RNA which in humans is encoded by the mitochondrial ''MT-TW'' gene.
Structure
The ''MT-TW'' gene is located on the p arm of the non-nuclear mitochondrial DNA at position ...
, MT-TV, MT-ND1
MT-ND1 is a gene of the mitochondrial genome coding for the NADH-ubiquinone oxidoreductase chain 1 (ND1) protein. The ND1 protein is a subunit of NADH dehydrogenase, which is located in the mitochondrial inner membrane and is the largest of the ...
, MT-ND2
MT-ND2 is a gene of the mitochondrial genome coding for the NADH dehydrogenase 2 (ND2) protein. The ND2 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the largest of the five ...
, MT-ND4
MT-ND4 is a gene of the mitochondrial genome coding for the NADH-ubiquinone oxidoreductase chain 4 (ND4) protein. The ND4 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the l ...
, MT-ND5
MT-ND5 is a gene of the mitochondrial genome coding for the NADH-ubiquinone oxidoreductase chain 5 protein (ND5). The ND5 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the la ...
, MT-ND6
MT-ND6 is a gene of the mitochondrial genome coding for the NADH-ubiquinone oxidoreductase chain 6 protein (ND6). The ND6 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane and is the la ...
and MT-CO3
Cytochrome c oxidase subunit III (COX3) is an enzyme that in humans is encoded by the ''MT-CO3'' gene. It is one of main transmembrane subunits of cytochrome c oxidase. It is also one of the three mitochondrial DNA (mtDNA) encoded subunits ( M ...
. Abnormalities in mitochondrial energy generation result in neurodegenerative disorders like Leigh syndrome, which is characterized by an onset of symptoms between 12 months and three years of age. The symptoms frequently present themselves following a viral infection and include movement disorders and peripheral neuropathy
Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...
, as well as hypotonia
Hypotonia is a state of low muscle tone (the amount of tension or resistance to stretch in a muscle), often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases a ...
, spasticity
Spasticity () is a feature of altered skeletal muscle performance with a combination of paralysis, increased tendon reflex activity, and hypertonia. It is also colloquially referred to as an unusual "tightness", stiffness, or "pull" of muscles.
...
and cerebellar ataxia
Cerebellar ataxia is a form of ataxia originating in the cerebellum. Non-progressive congenital ataxia (NPCA) is a classical presentation of cerebral ataxias.
Cerebellar ataxia can occur as a result of many diseases and may present with symptoms ...
. Roughly half of affected patients die of respiratory or cardiac failure by the age of three. Leigh syndrome
Leigh syndrome (also called Leigh disease and subacute necrotizing encephalomyelopathy) is an inherited neurometabolic disorder that affects the central nervous system. It is named after Archibald Denis Leigh, a British neuropsychiatrist who fir ...
is a maternally inherited disorder and its diagnosis is established through genetic testing of the aforementioned mitochondrial genes, including MT-ND3. These complex I
Respiratory complex I, (also known as NADH:ubiquinone oxidoreductase, Type I NADH dehydrogenase and mitochondrial complex I) is the first large protein complex of the Electron transport chain, respiratory chains of many organisms from bacteria to ...
genes have been associated with a variety of neurodegenerative disorders, including Leber's hereditary optic neuropathy
Leber's hereditary optic neuropathy (LHON) is a mitochondrially inherited (transmitted from mother to offspring) degeneration of retinal ganglion cells (RGCs) and their axons that leads to an acute or subacute loss of central vision; it predomin ...
(LHON), mitochondrial encephalomyopathy with stroke-like episodes (MELAS
Melas may refer to:
* Plural of mela
People
* Melas (mythology), a number of different characters in Greek mythology
* Pavlos Melas (1870–1904), a Hellenic Army officer and a symbol of the Greek Struggle for Macedonia
* Chloe Melas, an Ameri ...
) and the previously mentioned Leigh syndrome
Leigh syndrome (also called Leigh disease and subacute necrotizing encephalomyelopathy) is an inherited neurometabolic disorder that affects the central nervous system. It is named after Archibald Denis Leigh, a British neuropsychiatrist who fir ...
.
Interactions
MT-ND3 has been shown to have 5 binary protein-protein interactions including 2 co-complex interactions. MT-ND3 appears to interact with APP and NDUFA9
NADH dehydrogenase biquinone1 alpha subcomplex subunit 9 is an enzyme that in humans is encoded by the NDUFA9 gene. The NDUFA9 protein is a subunit of NADH:ubiquinone oxidoreductase (Complex I of the electron transport chain), which is located i ...
.
References
Further reading
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External links
Mass spectrometry characterization of MT-ND3 at COPaKB
{{Mitochondrial enzymes
Proteins
Human mitochondrial genes