Dyneins

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Nischal K. Karki
William Carey University

BIO 470
Cell Physiology
Dr. Douglas Lipka
Abstract
Dynein is an ATPase from ATP associated with various cell activities family. Cytoplasmic dynein transports various materials from outside the cell to the center body. It is one of the few proteins that can convert the chemical energy of ATP into mechanical. It is a massive macro molecule that is involved with the movement of various organelles within the cell. It is also involved with the movement of a cell in its surrounding, example: movement of spermatozoa using flagella and movement of paramecium using cilia. It has also been identified to be responsible for movement of vital organelles in a cell, for example: movement of organelles in nerve synapses. Thus, any dysfunction of dynein could result in major diseases. Dysfunction of cytoplasmic dynein has been found to be one of the factors of Alzheimer’s disease. Likewise, dysfunction of dynein in flagella has been tracked as one of many causes of infertility in men. It uses microtubule as a track for its movement and heads towards the negative terminal of the microtubule.

Before the 1940’s, actin and myosin based-system was considered responsible for all forms of motility shown by a eukaryotic cell. In 1945, the first account of myosin-like ATPase was recorded by Engelhard. The ATPase was named “spermosin” from bull sperm flagella. After this report many researchers examined the presence of myosin and actin in flagella and cilia. The breakthrough in the field happened during the 1960’s. Gibbons isolated the ATPase protein from Tetrahymena cilia. Since the ATPase displayed properties of isolated sperm flagella and not of myosin, he named the new protein as “dynein” . Dynein is a part of ATPase associated with diverse cellular activities or AAA family. AAA proteins usually are seen combining as a hexameric rings (six monomers) that carry out specific function as an enzyme. Similarly, dynein also has six distinct AAA domains that are connected with polypeptide chain. Electron microscopy shows that the AAA domains of heavy chains of dynein fold into a ring shaped structure similar to other ATPase . When talking about dynein, we need to first look at its track, microtubule. Microtubule is a part of cytoskeletal system that helps support and serve as a track for the transport of organelles along the cell. Microtubule is a polymer of dimer proteins of alpha and beta tubulins. The primary function of microtubule is for the transport of organelles. However, it also helps in functionality of cytoskeletal system. Cytoskeletal system is a collection of polymer chains that helps in maintaining the size, shape, and growth of a cell. The motor proteins related to microtubule are kinesins and dyneins. Microtubule usually has a positive and negative terminals which help guide the motor proteins. Molecular motors or motor proteins are primarily of two types, kinesins and dyneins. Kinesins are motor proteins that move towards the positive terminal whereas, dyneins move towards the negative terminal so the movement of kinesins is described as anterograde movement and the movement of dyneins are called retrograde movement. Although both of them are ATP activated motors, dyneins are of completely different protein family than kinesins . Dynein is a massive molecule with molecular weight of around 1,200,000 atomic mass units . It is a complex with heavy chains, light chains, and light intermediate chains. It usually consists of 2 heavy chains with ATP hydrolysis and microtubule binding sites and hence, is the major unit of dynein. Using electron microscopy, it has been established that the heavy chain folds into globular head with two elongated structures, stalk and stem, developing from it. The stalk binds to the microtubule track while the stem binds to the cargo . “In filamentous fungi, as well as in metazoans, dynamic microtubule plus ends are sites for cargo loading and...
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