The Myosin Classes


Phylogenetic tree analysis has led to the identification of a number of 'classes' of myosin proteins. As research progresses, the function of various members of these classes is being determined. On this page we show a graphical comparison of the classes and an indication of their function.

Note again that these classes are derived from the Hodge and Cope phylogenetic analysis. With the publication of the Foth et al tree, the total number of myosin classes is now up to 24!

The classes have been identified as a result of phylogenetic analysis of the core motor domain only, however, the most marked difference in sequence composition is to be found in the 'tail' regions, which are postulated to bind specific 'cargoes'. This leads to the conclusion that the tail and motor domains have co-evolved to their specific tasks.

The full-size version of the graphic to the left shows the current 16 classes of myosins and was produced using information from publications by Mooseker and Cheney, Kreis and Vale and Jim Sellers

Biological Function

For a fuller exposition of function with references, see Kreis and Vale or the more recent review by Jim Sellers which deals with classes II, IV, VI-VIII and X-XV.
For links to the sequences, see our accession page.

 Class  Function
 I - Amoeboid Cell motility, phagocytosis, contractile vacuole
 I - brush border Microvilli function, possibly vesicle transport
 IB Stereocilia function, vesicle transport?, epithelial development
 I - myr 4 Epithelial development, vesicle transport?
 II - cytoplasmic Cytokinesis, phagocytosis, cell shape and/or polarity
 II - smooth muscle Smooth muscle contraction
 II - sarcomeric Skeletal muscle contraction
 III Rhabdomere function (Drosophila), photoadaptation
 IV ???? Acanthamoeba species only.
 V Vesicle transport, mRNA transport
 VI Vesicle transport, hair cell function, epithelial function, reverse translocation of actin filaments.
 VII Sensory epithelia
 VIII - Plant ????
 IX Signal transduction
 X ???? Pleckstrin homology may indicate signal transduction role
 XI - Plant  Vesicle transport
 XII ????
 XIII - Plant ????
 XIV ???? Toxoplasma and Plasmodium species only
 XV Auditory?
 XVI Neuronal cell migration (Cameron, R.S pers comm)
 XVII ???? include chitin synthase domain, located in the plasma membrane. Pyricularia and Emiricella species only.



Mooseker, MS and Cheney, RE (1995) Unconventional myosins, Annu Rev Cell Dev Biol 11:633-675

Kreis, T and Vale, R (Eds) Guidebook to the Cytoskeletal and Motor Proteins, Second Edition (1999), Oxford University Press Inc, New York. ISBN 0 19 859956 0

Sellers, James R. (2000) Myosins: a Diverse Superfamily. Biochem. Biophys. Acta - Molecular Cell Research Volume 1496, pp3-22

Comments should be sent to Brooke Morriswood.

If you use diagrams, trees, or sequence alignments from the Myosin site, we ask that you cite either the Home Page and authors, or the appropriate source publication in your work.
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