Myosin: Difference between revisions

{{STRUCTURE_3i5f|  PDB=3i5f | SIZE=400| SCENE= |right|CAPTION=Squid myosin: heavy chain (grey),  regulatory light chain (green), catalytic light chain (pink) complex with ADP and Mg+2 ion [[3i5f]] }}

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[[Myosin]] is one of three major classes of molecular motor proteins: myosin, dynein, and kinesin.  As the most abundant of these proteins myosin plays a structural and enzymatic role in muscle contraction and intracellular motility. Myosin was first discovered in muscle in the 19th century. <ref name="Spudich">PMID: 8824453 </ref> Myosin is a superfamily of proteins which bind actin, hydrolyze ATP and transduce force.  Thus most are located in muscle cells.  Composed of head, neck and tail domains.  Head domain binds the actin and moves along it.  The neck is  a linker and binds the light chains which have a regulatory function.  The tail interacts with cargo molecules (CBD)m.  There are 18 classes of myosin. Myosin II (MII) is best studied and contains 2 heavy chains (HC)  which constitute the head or motor domain (MD) and the tail domain and 4 light chains (LC) which are referred to as the essential LC (ELC) and the regulatory LC (RLC). The images at the left and at the right correspond to one representative Myosin, ''i.e.'' the crystal structure of from Myosin ''Gallus gallus'' ([[2mys]]).

 

Myosin has a molecular size of approximately 520 kilodaltons with a total of six subunits.  It has two 220 kD heavy chains which make the majority of the overall structure and two pairs of light chains which vary in size.<ref name="Rayment" />  The molecule is asymmetric, having a long tail and two globular heads.  Each heavy chains composes the bulk of one of the globular heads.  Subfragment-1(S1) also termed the myosin head consists of ATP, actin, and two light chain binding sites. Each globular head has a heavy chain and two light chains for a combined molecular size of about 130 kD. <ref name="Rayment" />  

The myosin head is assymetrical with a length of 165 Angstroms and 65 Angstroms in width, with a total thickness of about 40 Angstroms. <ref name="Rayment" /> About 48% of the amino acid residues in the myosin head are dominated by α helices.  At the carboxyl terminus one long α helix of about 85 Angstroms extends in a left-handed coil. This particular helix forms the light chain binding region of the globular domain <ref name="Rayment" /> The amino terminus of each heavy chain has a large globular domain containing the site of ATP hydrolysis.   

 

 

[[1lkx]] – DdMI HC - ''Dictyostelium discoideum''<br />

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

==Literature Cited==