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Open Access Research article

Thirteen is enough: the myosins of Dictyostelium discoideum and their light chains

Martin Kollmar

Author Affiliations

Abteilung NMR basierte Strukturbiologie, Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, D-37077 Goettingen, Germany

BMC Genomics 2006, 7:183  doi:10.1186/1471-2164-7-183

Published: 20 July 2006

Abstract

Background

Dictyostelium discoideum is one of the most famous model organisms for studying motile processes like cell movement, organelle transport, cytokinesis, and endocytosis. Members of the myosin superfamily, that move on actin filaments and power many of these tasks, are tripartite proteins consisting of a conserved catalytic domain followed by the neck region consisting of a different number of so-called IQ motifs for binding of light chains. The tails contain functional motifs that are responsible for the accomplishment of the different tasks in the cell. Unicellular organisms like yeasts contain three to five myosins while vertebrates express over 40 different myosin genes. Recently, the question has been raised how many myosins a simple multicellular organism like Dictyostelium would need to accomplish all the different motility-related tasks.

Results

The analysis of the Dictyostelium genome revealed thirteen myosins of which three have not been described before. The phylogenetic analysis of the motor domains of the new myosins placed Myo1F to the class-I myosins and Myo5A to the class-V myosins. The third new myosin, an orphan myosin, has been named MyoG. It contains an N-terminal extension of over 400 residues, and a tail consisting of four IQ motifs and two MyTH4/FERM (

    my
osin
    t
ail
    h
omology
    4
/band
    4
.1,
    e
zrin,
    r
adixin, and
    m
oesin) tandem domains that are separated by a long region containing an SH3 (
    s
rc
    h
omology
    3
) domain. In contrast to previous analyses, an extensive comparison with 126 class-VII, class-X, class-XV, and class-XXII myosins now showed that MyoI does not group into any of these classes and should not be used as a model for class-VII myosins.

The search for calmodulin related proteins revealed two further potential myosin light chains. One is a close homolog of the two EF-hand motifs containing MlcB, and the other, CBP14, phylogenetically groups to the ELC/RLC/calmodulin (

    e
ssential
    l
ight
    c
hain/
    r
egulatory
    l
ight
    c
hain) branch of the tree.

Conclusion

Dictyostelium contains thirteen myosins together with 6–8 MLCs (

    m
yosin
    l
ight
    c
hain) to assist in a variety of actin-based processes in the cell. Although they are homologous to myosins of higher eukaryotes, the myosins of Dictyostelium should be considered with care as models for specific functions of vertebrate myosins.