Myosin head
Encyclopedia
Muscle
contraction
is caused by the sliding action of the thick filaments
over the thin filaments of the myofibril. Myosin
is a major component of thick filament
s and exists as a hexamer of 2 heavy chain
s, 2 alkali light chains, and 2 regulatory light chains. The heavy chain can be subdivided into the N-terminal globular head and the C-terminal coiled-coil
rod-like tail, although some forms have a globular region in their C-terminal. There are many cell-specific isoforms of myosin heavy chains, coded
for by a multi-gene family. Myosin interact
s with actin
to convert chemical energy, in the form of ATP, to mechanical energy
. The 3-D structure of the head portion of myosin has been determined and a model for actin-myosin complex
has been constructed.
The globular head is well conserved, and is key to contraction. Muscle contraction results from an attachment–detachment cycle between the myosin heads extending from myosin filaments and the sites on actin filaments. The myosin head first attaches to actin together with the products of ATP hydrolysis, performs a power stroke associated with release of hydrolysis products, and detaches from actin upon binding with new ATP. The detached myosin head then hydrolyses ATP, and performs a recovery stroke to restore its initial position. The strokes have been suggested to result from rotation of the lever arm domain around the converter domain, while the catalytic domain remains rigid.
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
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...
is caused by the sliding action of the thick filaments
Protein filament
In biology, a filament is a "long chain of proteins, such as those found in hair, muscle, or in flagella". They are often bundled together for strength and rigidity. Some cellular examples include:*Actin filaments*Microtubules*Intermediate filaments...
over the thin filaments of the myofibril. 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...
is a major component of thick filament
Protein filament
In biology, a filament is a "long chain of proteins, such as those found in hair, muscle, or in flagella". They are often bundled together for strength and rigidity. Some cellular examples include:*Actin filaments*Microtubules*Intermediate filaments...
s and exists as a hexamer of 2 heavy chain
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
s, 2 alkali light chains, and 2 regulatory light chains. The heavy chain can be subdivided into the N-terminal globular head and the C-terminal coiled-coil
Coiled coil
A coiled coil is a structural motif in proteins, in which 2-7 alpha-helices are coiled together like the strands of a rope . Many coiled coil type proteins are involved in important biological functions such as the regulation of gene expression e.g. transcription factors...
rod-like tail, although some forms have a globular region in their C-terminal. There are many cell-specific isoforms of myosin heavy chains, coded
Genetic code
The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....
for by a multi-gene family. Myosin interact
Protein-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...
s with 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...
to convert chemical energy, in the form of ATP, to mechanical energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
. The 3-D structure of the head portion of myosin has been determined and a model for actin-myosin complex
Protein complex
A multiprotein complex is a group of two or more associated polypeptide chains. If the different polypeptide chains contain different protein domain, the resulting multiprotein complex can have multiple catalytic functions...
has been constructed.
The globular head is well conserved, and is key to contraction. Muscle contraction results from an attachment–detachment cycle between the myosin heads extending from myosin filaments and the sites on actin filaments. The myosin head first attaches to actin together with the products of ATP hydrolysis, performs a power stroke associated with release of hydrolysis products, and detaches from actin upon binding with new ATP. The detached myosin head then hydrolyses ATP, and performs a recovery stroke to restore its initial position. The strokes have been suggested to result from rotation of the lever arm domain around the converter domain, while the catalytic domain remains rigid.