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MT-ND3 is a
gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
of the mitochondrial genome coding for the NADH dehydrogenase 3 (ND3) protein. The ND3 protein is a subunit of NADH dehydrogenase (ubiquinone), which is located in the mitochondrial inner membrane 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 which 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 Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), Leigh's syndrome (LS) and Leber's hereditary optic neuropathy (LHON).


Structure


General features

MT-ND3 is located in human
mitochondrial DNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the 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), together with MT-ND1, MT-ND2, MT-ND4, MT-ND4L, MT-ND5, and MT-ND6. 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 respiratory chains of many organisms from bacteria to humans. It catalyzes th ...
, this enzyme is the largest of the respiratory complexes. The structure is L-shaped with a long,
hydrophobic In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, thu ...
transmembrane A transmembrane protein 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 frequently u ...
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 n ...
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 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 respiratory chains of many organisms from bacteria to humans. It catalyzes th ...
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 ade ...
dehydrogenation and
electron transfer Electron transfer (ET) occurs when an electron relocates from an atom, ion, or molecule, to another such chemical entity. ET describes the mechanism by which electrons are transferred in redox reactions. Electrochemical processes are ET reactio ...
to
ubiquinone Coenzyme Q10 (CoQ10 ), also known as ubiquinone, is a naturally occurring Cofactor (biochemistry), biochemical cofactor (coenzyme) and an antioxidant produced by the human body. It can also be obtained from dietary sources, such as meat, fish, ...
(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 ade ...
binds to Complex I and transfers two electrons to the isoalloxazine ring 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 FMNH2. 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 (CoQH2). 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-TL1 Mitochondrially encoded tRNA leucine 1 (UUA/G) also known as MT-TL1 is a transfer RNA which in humans is encoded by the mitochondrial ''MT-TL1'' gene. Structure The ''MT-TL1'' gene is located on the p arm of the mitochondrial DNA at position 1 ...
, MT-TK,
MT-TW Mitochondrially encoded tRNA tryptophan also known as MT-TW is a transfer RNA which in humans is encoded by the mitochondrion, mitochondrial ''MT-TW'' gene. Structure The ''MT-TW'' gene is located on the Locus (genetics), p arm of the non-nucle ...
, MT-TV, MT-ND1, MT-ND2, MT-ND4, MT-ND5, MT-ND6 and MT-CO3. 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, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropa ...
, 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 it is a potential manifestation of many different dis ...
,
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. 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 Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...
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 respiratory chains of many organisms from bacteria to humans. It catalyzes th ...
genes have been associated with a variety of neurodegenerative disorders, including Leber's hereditary optic neuropathy (LHON), mitochondrial encephalomyopathy with stroke-like episodes ( MELAS) 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.


References


Further reading

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External links


Mass spectrometry characterization of MT-ND3 at COPaKB
{{Mitochondrial enzymes Proteins Human mitochondrial genes