Spasmin

In addition to the motor proteins myosin and dynein , spasmin is also a contractile protein and is around 20  kDa in size. So far it has only been detected in protozoa and is responsible here in particular for the movement of peritric ciliates .

For example, some sessile dinoflagellates and a heliozoon are attached to the substrate with contractile stems. The basis of the contraction is a stalk structure called a spasmonema . This lies in a cytoplasmic tube and extends from the cell body to the stem attachment to the substrate. The spasmonema is composed of ~ 3 nm thick subunits. These subunits consist primarily of spasmin molecules, which are arranged in the longitudinal direction of the stem. The protein could also be detected in peritrichi ciliates such as the bell animal Vorticella , Carchesium and Zoothamnium .

The protein spasmin consists largely of acidic amino acids and has the ability to bind calcium ions . The contraction of the spasmonema is induced by a release of calcium ions from the endoplasmic tubules surrounding the spasmonema. The concentration of the ions increases from 10 ⁻⁸ to 5 ^. 10 ⁻⁶ moles . Experiments carried out with the system in vitro have shown that ATP is only required indirectly for a contraction. The relaxation was due to the removal of calcium ions from the incubation medium. From this it can be concluded for the system in vivo that ATP is required for a mechanism which pumps the ions back into the endoplasmic tubules and thus enables the stem to return to its original length, whereby the high-energy original state of the spasmonema is restored.

Covering negative charges of the spasmin by the Ca ²⁺ ions is discussed as the underlying mechanism . These could accordingly result in a change in the conformation of the spasmin. This protein folding would then lead to a contraction.

See also

• Tubulin
• Actin
• Motor protein
• Contractile Mechanism

swell

• Heinz Penzlin: Textbook of animal physiology. 7th edition. Elsevier Spektrum Akademischer Verlag, Munich 2005, ISBN 3-8274-0170-4 . (EA Jena 1970)

further reading

• T. Itabashi, K. Mikami, H. Asai: Characterization of the spasmin 1 gene in Zoothamnium arbuscula strain Kawagoe (protozoa, ciliophora) and its relation to other spasmins and centrins. In: Research in Microbiology. 154, 2003, pp. 361-367. doi: 10.1016 / S0923-2508 (03) 00050-0
• T. Ochiai, M. Kato, T. Ogawa, H. Asai1: Spasmin-like proteins in various ciliates revealed by antibody to purified spasmins of Carchesium polypinum. In: Experientia. 44, 1988, p. 768.