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The Myosins 

Page updated 26/5/02

A group of actin-binding proteins that produce movement typically toward the barbed end with respect to the actin filament. Myosins play an enormously diversity of motile functions in cells from muscle contraction to phagocytosis.  The myosins share a conserved head domain that binds actin and produces motility by ATP-hydrolysis- mediated conformational changes whose amplitude is amplified by levers comprised of  "neck" regions supported and regulated by, typically calmodulin-like light chains.  The first myosin (myosin II) was isolated in from muscle, however many years later the first of the so called "unconventional" myosins was isolated from the soil amoeba Acanthamoeba castellanii by Tom Pollard and Ed Korn (Pollard & Korn, 1973).  To date in the region of 18 different myosins are recognised in nature, some are restricted to plants, others as far as is known to acomplexans and there are some 40 genes in 12 classes of myosins in the human genome (Berg et al, 2001).  The classes of myosins have been determined by phylogenetic analysis of the moderately conserved myosin "head" region and happily this seems to fit reasonably well with the overall structure.  Naturally, with the advent of PCR and genomic sequencing projects, knowledge of the existence of these sequences and their identity far outstrips the knowledge of what functions these diverse proteins perform.  This is "proteomics"  (it used to be called Biochemistry!).
        There are currently some 18 (or so)  recognised myosin families :-        
Myosin I Myosin II Myosin III (nina C)
Myosin IV Myosin V Myosin VI
Myosin VII Myosin VIII Myosin IX
Myosin X Myosin XI Myosin XII
Myosin XIII Myosin XIV Myosin XV
Myosin XVI Myosin XVII Myosin XVIII
Myosins presently unclassified
Speed & Direction of  the Myosins How Myosins Move Myosins and Human Disease


Berg, J. S., Powell, B. C. & Cheney, R. E. (2001) A millennial myosin census. Mol.Biol.Cell. 12, 780-794.

Pollard, T.D. & Korn, E.D. (1973) Acanthamoeba myosin. I. Isolation from Acanthamoeba castellanii of an enzyme similar to muscle myosin. J.Biol.Chem. 248, 4682-4690.

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