The syntrophins are a family of five 60-kiloDalton

Atomic mass unit

The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...

 protein

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...

s that are associated with dystrophin

Dystrophin

Dystrophin is a rod-shaped cytoplasmic protein, and a vital part of a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane. This complex is variously known as the costamere or the dystrophin-associated protein complex...

, the protein associated with Duchenne muscular dystrophy

Duchenne muscular dystrophy

Duchenne muscular dystrophy is a recessive X-linked form of muscular dystrophy, which results in muscle degeneration, difficulty walking, breathing, and death. The incidence is 1 in 3,000 boys. Females and males are affected, though females are rarely affected and are more often carriers...

 and Becker muscular dystrophy. The name comes from the Greek word syntrophos, meaning "companion." The five syntrophins are encoded by separate 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...

s and are termed α, β1, β2, γ1, and γ2. Syntrophin was first identified as a dystrophin-associated protein present in torpedo electric organ (originally called "58K protein"). Subsequently, alpha syntrophin was shown to be the predominant isoform in skeletal muscle

Skeletal 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...

 where it is localized on the sarcolemma

Sarcolemma

The sarcolemma is the cell membrane of a muscle cell . It consists of a true cell membrane, called the plasma membrane, and an outer coat made up of a thin layer of polysaccharide material that contains numerous thin collagen fibrils...

 and enriched at the neuromuscular junction

Neuromuscular junction

A neuromuscular junction is the synapse or junction of the axon terminal of a motor neuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscle's surface, ultimately causing the muscle to contract...

. The beta syntrophins and γ2 syntrophin are also present in skeletal muscle but also are in most other tissues. The expression of γ1 syntrophin is mostly confined to brain. The syntrophins are adapter proteins that use their multiple protein interaction domain

Protein domain

A protein domain is a part of protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Many proteins consist of several structural...

s (two pleckstrin homology domain

Pleckstrin homology domain

Pleckstrin homology domain is a protein domain of approximately 120 amino acids that occurs in a wide range of proteins involved in intracellular signaling or as constituents of the cytoskeleton....

s and a PDZ domain

PDZ domain

The PDZ domain is a common structural domain of 80-90 amino-acids found in the signaling proteins of bacteria, yeast, plants, viruses and animals...

) to localize a variety of signaling proteins (kinase

Kinase

In chemistry and biochemistry, a kinase is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific substrates, a process referred to as phosphorylation. Kinases are part of the larger family of phosphotransferases...

s, ion channel

Ion channel

Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...

s, water channel

Water channel

Main article: Ship model basinA water channel is an experimental tank for studying resistance and propulsion behaviour of ships, submarines, or other sea vessels. In the study of naval architecture , its general purpose is to allow understanding of the motion behavior of ships in advance....

s, nitric oxide synthase

Nitric oxide synthase

Nitric oxide synthases are a family of enzymes that catalyze the production of nitric oxide from L-arginine. NO is an important cellular signaling molecule, having a vital role in many biological processes...

) to specific intracellular locations.