Cytochrome c oxidase assembly factor COX20 is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

that in humans is encoded by the COX20

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 b ...

. This gene encodes a protein that plays a role in the assembly of

cytochrome c oxidase The enzyme cytochrome c oxidase or Complex IV, (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and mitochondria of eukaryotes. It is the last enzyme in the respiratory elect ...

, an important component of the respiratory pathway. Mutations in this gene can cause mitochondrial

complex IV The enzyme cytochrome c oxidase or Complex IV, (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and mitochondria of eukaryotes. It is the last enzyme in the respiratory electr ...

deficiency. There are multiple pseudogenes for this gene. Alternative splicing results in multiple

transcript variants Alternative splicing, or alternative RNA splicing, or differential splicing, is an alternative splicing process during gene expression that allows a single gene to code for multiple proteins. In this process, particular exons of a gene may be ...

Structure

The ''COX20'' gene is located on the

q arm In genetics, a locus (plural loci) is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total ...

chromosome 1 Chromosome 1 is the designation for the largest human chromosome. Humans have two copies of chromosome 1, as they do with all of the autosomes, which are the non- sex chromosomes. Chromosome 1 spans about 249 million nucleotide base pairs, which ...

at position 44 and it spans 9,757 base pairs. The ''COX20'' gene produces a 13.3 kDa protein composed of 118 amino acids. It contains two

transmembrane helices A transmembrane domain (TMD) is a membrane-spanning protein domain. TMDs generally adopt an alpha helix topological conformation, although some TMDs such as those in porins can adopt a different conformation. Because the interior of the lipid bi ...

and localizes to the mitochondrial membrane.

Function

The ''COX20'' gene encodes for a

required for the assembly of

(complex IV).

Complex IV The enzyme cytochrome c oxidase or Complex IV, (was , now reclassified as a translocasEC 7.1.1.9 is a large transmembrane protein complex found in bacteria, archaea, and mitochondria of eukaryotes. It is the last enzyme in the respiratory electr ...

is the terminal complex of the

mitochondrial respiratory 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 thi ...

which is required for catalyzing the oxidation of cytochrome c by

molecular oxygen There are several known allotropes of oxygen. The most familiar is molecular oxygen (O2), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (O3). Others are: * ...

. COX20 is known to act as a

chaperone protein In molecular biology, molecular chaperones are proteins that assist the conformational folding or unfolding of large proteins or macromolecular protein complexes. There are a number of classes of molecular chaperones, all of which function to assi ...

during the early stages of

COX2 Cytochrome c oxidase subunit 2, also known as cytochrome c oxidase polypeptide II, is a protein that in humans is encoded by the MT-CO2 gene. Cytochrome c oxidase subunit II, abbreviated COXII, COX2, COII, or MT-CO2, is the second subunit of c ...

(cytochrome c oxidase subunit II) maturation which leads to the stabilization of the protein. By presenting

to the metallochaperones

SCO1 Protein SCO1 homolog, mitochondrial, also known as SCO1, cytochrome c oxidase assembly protein, is a protein that in humans is encoded by the ''SCO1'' gene. SCO1 localizes predominantly to blood vessels, whereas SCO2 is barely detectable, as well ...

and

SCO2 SCO2 cytochrome c oxidase assembly (also known as SCO2 homolog, mitochondrial and SCO cytochrome oxidase deficient homolog 2) is a protein that in humans is encoded by the ''SCO2'' gene. The encoded protein is one of the cytochrome c oxidase (CO ...

, they help facilitate the incorporation of the mature

into the

holoenzyme assembly. However, it has been known that COX20 has no influence on

transcription Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including: Genetics * Transcription (biology), the copying of DNA into RNA, the fir ...

translation Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...

or any other genes. The knockdown of the protein COX20 has been shown to result in reduced respiratory capacity and the accumulation of respiratory chain intermediates.

Clinical significance

Variants of ''COX20'' have been associated with the mitochondrial

deficiency, a deficiency in an enzyme complex of the

which catalyzes the oxidation of cytochrome c utilizing

. The deficiency is characterized by heterogeneous

phenotypes In genetics, the phenotype () is the set of observable characteristics or phenotypic trait, traits of an organism. The term covers the organism's morphology (biology), morphology or physical form and structure, its Developmental biology, dev ...

ranging from isolated myopathy to severe

multisystem disease A systemic disease is one that affects a number of Organ (anatomy), organs and Tissue (biology), tissues, or affects the Human body, body as a whole. Examples * Mastocytosis, including mast cell activation syndrome and eosinophilic esophagitis ...

affecting several tissues and organs. Other Clinical Manifestations include hypertrophic cardiomyopathy,

hepatomegaly Hepatomegaly is the condition of having an enlarged liver. It is a non-specific medical sign having many causes, which can broadly be broken down into infection, hepatic tumours, or metabolic disorder. Often, hepatomegaly will present as an abdo ...

and

liver dysfunction Liver disease, or hepatic disease, is any of many diseases of the liver. If long-lasting it is termed chronic liver disease. Although the diseases differ in detail, liver diseases often have features in common. Signs and symptoms Some of the s ...

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 ...

, muscle weakness,

exercise intolerance Exercise intolerance is a condition of inability or decreased ability to perform physical exercise at the normally expected level or duration for people of that age, size, sex, and muscle mass. It also includes experiences of unusually severe pos ...

developmental delay Global developmental delay is an umbrella term used when children are significantly delayed in their cognitive and physical development. It can be diagnosed when a child is delayed in one or more milestones, categorised into motor skills, speech ...

, delayed motor development and

mental retardation Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation, Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by signifi ...

. A homozygous mutation of c.154A-C in the ''COX20'' gene has been found to result in reduced COX20,

, and decreased activity. Other mutations have included a homozygous T52P.

Interactions

COX20 has co-complex interactions with proteins such as TMEM177,

, COA6, and others in a

and COX18 dependent manner.

Structure

Function

Clinical significance

Interactions

References

Further reading