Kinesin is a microtubule-associated force-producing protein that may play a role in organelle transport. The kinesin motor activity is directed toward the microtubule's plus end. Kinesin is an oligomeric complex composed of two heavy chains and two light chains. The maintenance of the quaternary structure does not require interchain disulphide bonds.The heavy chain is composed of three structural domains: a large globular N-terminal domain which is responsible for the motor activity of kinesin (it is known to hydrolyse ATP to bind and move on microtubules) a central alpha-helical coiled coil domain that mediates the heavy chain dimerisation; and a small globular C-terminal domain which interacts with other proteins (such as the kinesin light chains) vesicles and membranous organelles.A number of proteins have been recently found that contain a domain similar to that of the kinesin 'motor' domain :
- Drosophila melanogaster claret segregational protein (ncd). Ncd is required for normal chromosomal segregation in meiosis in females and in early mitotic divisions of the embryo. The ncd motor activity is directed toward the microtubule's minus end.
- Homo sapiens CENP-E . CENP-E is a protein that associates with kinetochores during chromosome congression relocates to the spindle midzone at anaphase and is quantitatively discarded at the end of the cell division. CENP-E is probably an important motor molecule in chromosome movement and/or spindle elongation.
- H. sapiens mitotic kinesin-like protein-1 (MKLP-1) a motor protein whose activity is directed toward the microtubule's plus end.
- Saccharomyces cerevisiae KAR3 protein which is essential for nuclear fusion during mating. KAR3 may mediate microtubule sliding during nuclear fusion and possibly mitosis.
- S. cerevisiae CIN8 and KIP1 proteins which are required for the assembly of the mitotic spindle. Both proteins seem to interact with spindle microtubules to produce an outwardly directed force acting upon the poles.
- Emericella nidulans (Aspergillus nidulans) bimC which plays an important role in nuclear division.
- A. nidulans klpA.
- Caenorhabditis elegans unc-104 which may be required for the transport of substances needed for neuronal cell differentiation.
- C. elegans osm-3.
- Xenopus laevis Eg5 which may be involved in mitosis.
- Arabidopsis thaliana KatA KatB and katC.
- Chlamydomonas reinhardtii FLA10/KHP1 and KLP1. Both proteins seem to play a role in the rotation or twisting of the microtubules of the flagella.
- C. elegans hypothetical protein T09A5.2.
The kinesin motor domain is located in the N-terminal part of most of the above proteins with the exception of KAR3 klpA and ncd where it is located in the C-terminal section.The kinesin motor domain contains about 330 amino acids. An ATP-binding motif of type A is found near position 80 to 90 the C-terminal half of the domain is involved in microtubule-binding.