ACTN3
Encyclopedia
Alpha-actinin-3, also known as alpha-actinin skeletal muscle isoform 3 or F-actin cross-linking protein, is a protein
that in humans is encoded by the ACTN3 gene
.
Alpha-actinin is an actin
-binding protein with multiple roles in different cell types. This gene expression is limited to skeletal muscle. It is localized to the Z-disc and analogous dense bodies, where it helps to anchor the myofibrillar actin filaments.
is composed of long cylindrical cells called muscle fibers. There are two types of muscle fibers, slow twitch or muscle contraction
(type I) and fast twitch (type II). Slow twitch fibers are more efficient in using oxygen to generate energy whilst fast twitch fibers are less efficient. However, fast twitch fibers fire more rapidly and generate more force.These are also called the white muscle fibers and red muscles fibers respectively.
(thin filaments) and myosin
(thick filaments) which are arranged in parallel. A muscle contraction involves these filaments sliding past each other.
Actin filaments are stabilized by actin binding proteins known as actinins of which there are two main types, type 2 and type 3. Each of these is encoded by a specific gene, ACTN2 and ACTN3 respectively.
ACTN2 is expressed in all skeletal muscle fibers whereas ACTN3 is expressed only in fast twitch fibers.
(rs1815739; R577X) has been identified in the ACTN3 gene which results in a deficiency of alpha-actinin 3 in a significant proportion of the population. Based on ethnicity the deficiency is found in 20-50% of people. Generally, Africans have the lowest incidence of the mutation whilst Asians have the highest. Scientists believe that variations in this gene evolved to accommodate the energy expenditure requirements of people in various parts of the world.
Studies have linked the fiber twitch type with ACTN3, i.e. fast twitch fiber abundant individuals carry the non-mutant gene version. Also, studies in elite athletes have shown that the ACTN3 gene may influence athletic performance. Whilst the non-mutant version of the gene is associated with sprint performance, the mutant version is associated with endurance.
with Actinin, alpha 2
.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that in humans is encoded by the ACTN3 gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
Alpha-actinin is an actin
Actin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
-binding protein with multiple roles in different cell types. This gene expression is limited to skeletal muscle. It is localized to the Z-disc and analogous dense bodies, where it helps to anchor the myofibrillar actin filaments.
Fast versus slow twitch muscle fibers
Skeletal muscleSkeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
is composed of long cylindrical cells called muscle fibers. There are two types of muscle fibers, slow twitch or muscle contraction
Muscle contraction
Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
(type I) and fast twitch (type II). Slow twitch fibers are more efficient in using oxygen to generate energy whilst fast twitch fibers are less efficient. However, fast twitch fibers fire more rapidly and generate more force.These are also called the white muscle fibers and red muscles fibers respectively.
ACTN3 in muscle fiber
Each muscle fiber is composed of long tubes called myofibrils which in turn are composed of filaments. There are two types of filaments: actinActin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
(thin filaments) and myosin
Myosin
Myosins comprise a family of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility processes. They are responsible for actin-based motility. The term was originally used to describe a group of similar...
(thick filaments) which are arranged in parallel. A muscle contraction involves these filaments sliding past each other.
Actin filaments are stabilized by actin binding proteins known as actinins of which there are two main types, type 2 and type 3. Each of these is encoded by a specific gene, ACTN2 and ACTN3 respectively.
ACTN2 is expressed in all skeletal muscle fibers whereas ACTN3 is expressed only in fast twitch fibers.
The rs1815739 mutation
A mutationMutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
(rs1815739; R577X) has been identified in the ACTN3 gene which results in a deficiency of alpha-actinin 3 in a significant proportion of the population. Based on ethnicity the deficiency is found in 20-50% of people. Generally, Africans have the lowest incidence of the mutation whilst Asians have the highest. Scientists believe that variations in this gene evolved to accommodate the energy expenditure requirements of people in various parts of the world.
Studies have linked the fiber twitch type with ACTN3, i.e. fast twitch fiber abundant individuals carry the non-mutant gene version. Also, studies in elite athletes have shown that the ACTN3 gene may influence athletic performance. Whilst the non-mutant version of the gene is associated with sprint performance, the mutant version is associated with endurance.
Interactions
ACTN3 has been shown to interactProtein-protein interaction
Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...
with Actinin, alpha 2
Actinin, alpha 2
Actinin, alpha 2, also known as ACTN2, is a protein which in humans is encoded by the ACTN2 gene.- Function :Alpha actinins belong to the spectrin gene superfamily which represents a diverse group of cytoskeletal proteins, including the alpha and beta spectrins and dystrophins. Alpha actinin is an...
.