| 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!). |
|
References:-
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. |
