Motor protein

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nanoscales

Motor proteins are a class of

molecular motors that can move along the cytoskeleton of cells. They convert chemical energy into mechanical work by the hydrolysis of ATP. Flagellar rotation, however, is powered by a proton pump.[citation needed
]

Cellular functions

The action of myosin along the actin filaments causes the shortening and lengthening of the sarcomere; responsible for muscle contraction and relaxation, respectively.

Motor proteins are the driving force behind most

spermatozoa
, and fluid transport, for example in trachea. The muscle protein myosin "motors" the contraction of muscle fibers in animals.

Diseases associated with motor protein defects

The importance of motor proteins in cells becomes evident when they fail to fulfill their function. For example,

cilia fail to function without dynein. Numerous myosin deficiencies are related to disease states and genetic syndromes. Because myosin II is essential for muscle contraction, defects in muscular myosin predictably cause myopathies. Myosin is necessary in the process of hearing because of its role in the growth of stereocilia so defects in myosin protein structure can lead to Usher syndrome and non-syndromic deafness.[1]

Cytoskeletal motor proteins

Motor proteins utilizing the

microtubules. Actin motors such as myosin move along microfilaments through interaction with actin, and microtubule motors such as dynein and kinesin move along microtubules through interaction with tubulin
.

There are two basic types of microtubule motors: plus-end motors and minus-end motors, depending on the direction in which they "walk" along the microtubule cables within the cell.

Actin motors

Myosin

Myosin V is involved in vesicle and organelle transport.[2][3] Myosin XI is involved in cytoplasmic streaming, wherein movement along microfilament networks in the cell allows organelles and cytoplasm to stream in a particular direction.[4] Eighteen different classes of myosins are known.[5]

Genomic representation of myosin motors:[6]

Microtubule motors

Kinesin

eukaryotic cells. Kinesins have two heavy chains and two light chains per active motor. The two globular head motor domains in heavy chains can convert the chemical energy of ATP hydrolysis into mechanical work to move along microtubules.[7] The direction in which cargo is transported can be towards the plus-end or the minus-end, depending on the type of kinesin. In general, kinesins with N-terminal motor domains move their cargo towards the plus ends of microtubules located at the cell periphery, while kinesins with C-terminal motor domains move cargo towards the minus ends of microtubules located at the nucleus. Fourteen distinct kinesin families are known, with some additional kinesin-like proteins that cannot be classified into these families.[8]

Genomic representation of kinesin motors:[6]

Dynein

flagella by rapid and efficient sliding movements of microtubules. Another branch is cytoplasmic dyneins which facilitate the transport of intracellular cargos. Compared to 15 types of axonemal dynein, only two cytoplasmic forms are known.[10]

Genomic representation of dynein motors:[6]

Plant-specific motors

In contrast to

fungi and non-vascular plants, the cells of flowering plants lack dynein motors. However, they contain a larger number of different kinesins. Many of these plant-specific kinesin groups are specialized for functions during plant cell mitosis.[11] Plant cells differ from animal cells in that they have a cell wall. During mitosis, the new cell wall is built by the formation of a cell plate starting in the center of the cell. This process is facilitated by a phragmoplast, a microtubule array unique to plant cell mitosis. The building of cell plate and ultimately the new cell wall requires kinesin-like motor proteins.[12]

Another motor protein essential for plant cell division is kinesin-like calmodulin-binding protein (KCBP), which is unique to plants and part kinesin and part myosin.[13]

Other molecular motors

Main article:
Molecular motors

Besides the motor proteins above, there are many more types of proteins capable of generating forces and torque in the cell. Many of these molecular motors are ubiquitous in both prokaryotic and eukaryotic cells, although some, such as those involved with cytoskeletal elements or chromatin, are unique to eukaryotes. The motor protein prestin,[14] expressed in mammalian cochlear outer hair cells, produces mechanical amplification in the cochlea. It is a direct voltage-to-force converter, which operates at the microsecond rate and possesses piezoelectric properties.

See also

References

  1. PMID 14559185
    .
  2. ^ Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002-01-01). "Molecular Motors". NCBI - National Institutes of Health.
  3. PMID 22291143
    .
  4. PMID 22566666
    .
  5. S2CID 635349
    .
  6. ^
    PMID 12600311
    .
  7. PMID 21332353
    .
  8. PMID 16084724
    .
  9. PMID 24064538
    .
  10. S2CID 14240073
    .
  11. PMID 16530461
    .
  12. PMID 11909547
    .
  13. PMID 15951483
    .
  14. S2CID 7333228
    .

External links
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