Alpha-actinin-3, also known as alpha-actinin skeletal muscle isoform 3 or F-actin cross-linking protein, is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
that in humans is encoded by the ''ACTN3''
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 ...
(named sprinter gene, speed gene or athlete gene) located on
chromosome 11. All people have two copies (alleles) of this 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.
Fast versus slow twitch muscle fibers
Skeletal muscle 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, while fast twitch fibers are less efficient. However, fast twitch fibers fire more rapidly, allowing them to generate more power than slow twitch (type I) fibers. Fast twitch fibers and slow twitch fibers are also called white muscle fibers and red muscles fibers, respectively. The alpha-actinin-3 protein is found in type II muscle fibers.
Alleles
An
allele
An allele is a variant of the sequence of nucleotides at a particular location, or Locus (genetics), locus, on a DNA molecule.
Alleles can differ at a single position through Single-nucleotide polymorphism, single nucleotide polymorphisms (SNP), ...
(rs1815739; 577X) has been identified in the ACTN3 gene which results in a deficiency of alpha-actinin-3 in the individuals.
The X
homozygous genotype (ACTN3 577XX) is caused by a C to T transition in
exon 16 of the ''ACTN3''
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 ...
, which causes a transformation of an
arginine base (R) to a premature
stop codon (X) resulting in the rs1815739
mutation causing no production of the alpha-actinin 3 protein in muscle fibers.
The 577XX
polymorphism causes no production of alpha-actinin 3 protein which is essential in fast twitch muscle fibers.
It has been speculated that variations in this gene evolved to accommodate the energy expenditure requirements of people in various parts of the world.
Over 75% of the persons have one or two copies of ACTN3 577R and have alpha-actinin-3. Homozygous individuals (ACTN3 577XX) have no alpha-actinin-3 (16%-20% of the population),
but they have a high level of
alpha-actinin-2.
Athletes
There is an association between the ''ACTN3'' R577X
polymorphism in sprint and powerlifting performance at an elite level (RR and RX variants are better), and appears to be an association with exercise recovery and lower injury risk.
It appears that the XX genotype is associated with higher levels of muscle damage and a longer time required for recovery.
Interactions
ACTN3 has been shown to
interact with alpha-actinin-2.
See also
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Actinin
References
Further reading
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External links
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{{Cytoskeletal Proteins
Genes on human chromosome 11
EF-hand-containing proteins