Dynamin is a GTPase thought to be responsible for endocytosis in the eukaryotic cell, and is involved in vesicle (biology) trafficking both at the cell surface (particularly caveolae internalization) as well as at the Golgi (1)(2)(4). It is a 100 kDa enzyme, and was first isolated while researchers attempted to isolate new microtubule-based motors from the bovine brain, and, to date, has best been studied within clathrin-coated vesicle budding from the cell membrane (3)(4). GTPases are a large family of enzymes that can bind and hydrolyze GTP. The GTP binding and hydrolysis takes place in the highly conserved G domain common to all GTPases. ... Endocytosis is a process whereby cells absorb material (molecules such as proteins) from the outside by engulfing it with their cell membrane. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... In biology, caveolae (Latin for little caves) are small invaginations of the plasma membrane in many cell types, especially in endothelial cells. ... In cell biology, the Golgi apparatus, Golgi body, Golgi complex, or dictyosome is an organelle found in most eukaryotic cells, including those of plants, animals, and fungi. ... The atomic mass unit (amu), unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic masses and molecular masses. ... Clathrin is a protein that is the major constituent of the coat of the coated pits and coated vesicles formed during endocytosis of materials at the surface of cells. ... Drawing of a cell membrane A cell membrane, plasma membrane or plasmalemma is a selectively permeable lipid bilayer coated by proteins which comprises the outer layer of a cell. ...

To see a cartoon image of the way dynamin is thought to work within the cell, please follow this link: http://www.fasebj.org/cgi/content/full/13/9002/S243/F1 (1).

How does dynamin work?

As a vesicle invaginates, dynamin forms a spiral around the neck of the vesicle. Once the spiral is in place, it extends lengthwise and constricts through GTP hydrolysis (when guanosine triphosphate is converted to guanosine diphosphate). This lengthening and tightening of the coil around the vesicle neck causes it to break and results in the pinching off of the vesicle from the parent membrane (2)(3). Guanosine triphosphate (GTP) is also known as guanosine-5-triphosphate. ... Guanosine diphosphate, abbreviated GDP, is a nucleotide. ...

To view a picture of dynamin assembled into spirals, please follow this link: http://dynamin.niddk.nih.gov/figure1.html (2).

To view the effect of GTP and GDP on dynamin spirals, please follow this link: http://dynamin.niddk.nih.gov/figure2.html (2). In part A of this picture we see dynamin tubes while they are in the presence of GTP; they are large and relaxed. In part B of the picture we see the same dynamin tubes from part one, but in the presence of GDP; they are tight. This is how dynamin works to pinch vesicles off from the membrane.

To view a ‘cartoon’ image of the non-constricted and constricted state of dynamin spirals, please follow this link: http://dynamin.niddk.nih.gov/figure5.jpg (2). The first structure on the left is dynamin in its relaxed state. The structure on the right is dynamin in its constricted state. This allows you to see how much dynamin tightens and changes when GTP is converted to GDP.

Different types of dynamins

In mammals, three different dynamin genes have been identified. Dynamin I is expressed in neurons and neuroendocrine cells; Dynamin II is expressed in most cell types; Dynamin III is expressed mainly in the testis, but also in the heart, brain, and lungs (1).

Dynamin is part of a ‘’Dynamin Superfamily’’ that includes classical dynamins, dynamin-like proteins, Mx proteins, OPA, mitofusins, and GBPs (3).

To see a picture of where in the cell members of the dynamin superfamily are expressed, please follow this link: http://www.pnas.org/cgi/content/full/94/2/377/F5 (4).

References

(1) Henley, J.R., Cao, H., McNicven, M.A. (1999). “Participation of dynamin in the biogenesis of cytoplasmic vesicles”. The FASEB Journal, 13, S243-S247. http://www.fasebj.org/cgi/content/full/13/9002/S243 accessed 021806.

(2) Hinshaw, J. “Dynamin overview: The Role of Dynamin in Membrane Fission”. National institute of diabetes & digestive & kidney diseases, Laboratory of cell biochemistry and biology. http://dynamin.niddk.nih.gov/ accessed 021806.

(3) McMahon. (2004). “Researching Endocytic Mechanisms: Dynamin:. Accompaniment of Nature Reviews on Molecular Cell Biology, 5, 133-147. http://www.endocytosis.org/Dynamin/index.html accessed 021806.

(4) Urrutia, R., Henley, J.R., Cook, T., McNiven, M.A. (1997). “The dynamins: Redundant or distinct functions for an expanding family of related GTPases?” Proc. Natl. Acad. Sci. USA, Vol. 94, 377-384. http://www.pnas.org/cgi/content/full/94/2/377?ijkey=cc76b66f40ce6a1c4bef3246109754c5ca3cc425 accessed 021806.