Kinesin protein



Keywords: kinesin protein
Description: Note: Page numbers for this topic refer to the textbook Molecular Biology of the Cell by Alberts et al. (A). For additional information see the page on microtubules . Two main classes of

Note: Page numbers for this topic refer to the textbook Molecular Biology of the Cell by Alberts et al. (A). For additional information see the page on microtubules .

Two main classes of microtubule motor proteins carry out ATP-dependent movement along microtubules (A. p. 952-953):

  • Kinesins are a large family of motor proteins, most of which walk along microtubules toward the plus end. away from the centrosome (MTOC).
  • Dyneins walk along microtubules toward the minus end (toward the centrosome).

In each case there is postulated to be a reaction cycle similar (but not identical) to that of myosin. Motility arises from conformational changes in the motor domain as ATP is bound and hydrolyzed, and products are released.

Kinesins are a large family of proteins with diverse structures. Mammalian cells have at least 40 different kinesin genes. The best studied is referred to as conventional kinesin, kinesin I. or simply kinesin. Some are referred to as kinesin-related proteins (KRPs).

Kinesin I (conventional type) has a structure somewhat analogous to but distinct from that of myosin. There are 2 copies each of a heavy chain and a light chain.

Stalk domains of the heavy chains interact in an a -helical coiled coil that extends from the heavy chain neck to the tail. The coiled coil is interrupted by a few hinge regions that give flexibility to the otherwise stiff stalk domain.

N-termini of the two light chains associate with the two heavy chains near the tail. The diagram above is over simplified. Light chains at the N-terminus include a series of hydrophobic heptad repeats that are predicted to interact with similar repeats in heavy chains near the tail region, in a 4-helix coiled coil.

C-terminal tail domains of kinesin light chains include several "tetratrico peptide repeats" (TPRs). The 34 amino acid TPRs mediate protein-protein interactions. Kinesin light chain TPR repeats are involved in binding of kinesins to cargo. C terminal domains of heavy chains may also participate in binding some kinesins to cargo.

  • Some organelle membranes contain transmembrane receptor proteins that bind kinesins. Kinectin is an endoplasmic reticulum membrane receptor for kinesin-I.
  • Scaffolding proteins. first identified as being involved in assembling signal protein complexes, mediate binding of kinesin light chains to some cargo proteins or receptors.
  • Some membrane-associated Rab GTPases, that provide specificity for vesicle transport and fusion, are known to bind particular kinesins.

In the absence of cargo. the kinesin heavy chain stalk folds at hinge regions, bringing heavy chain tail domains into contact with the motor domains. In this folded over state, kinesin exhibits decreased ATPase activity and diminished binding to microtubules. This may prevent wasteful hydrolysis of ATP by kinesin when it is not transporting cargo.

Unfolding of kinesin into its more extended active conformation is promoted by phosphorylation of kinesin light chains, catalyzed by a specific kinase, or binding of cargo.




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