dictyNews
Electronic Edition
Volume 36, number 17
June 24, 2011
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Abstracts
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Self-recognition in social amoebae is mediated by allelic pairs of tiger genes
Shigenori Hirose*, Rocio Benabentos*, Hsing-I Ho, Adam Kuspa# and
Gad Shaulsky#
Baylor College of Medicine, Houston, TX
* equal contribution; # corresponding authors
Science, in press
Abstract: Free-living cells of the social amoebae Dictyostelium discoideum
can aggregate and develop into multicellular fruiting bodies in which many
altruistically die as they become stalk cells that support the surviving spores.
Dictyostelium cells exhibit kin-discrimination – a potential defense against
cheaters, which sporulate without contributing to the stalk. Kin-discrimination
depends on strain relatedness and the polymorphic genes tgrB1 and tgrC1
are potential components of that mechanism. Here we demonstrate a direct
role for these genes in kin-discrimination. We show that a matching pair of
tgrB1 and tgrC1 alleles is necessary and sufficient for attractive
self-recognition, which is mediated by differential cell-cell adhesion. We
propose that TgrB1 and TgrC1 proteins mediate this adhesion through
direct binding. This system is a genetically-tractable ancient model of
eukaryotic self-recognition.
Submitted by Gad Shaulsky [[log in to unmask]]
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Identification of Calmodulin and MlcC as Light Chains for Dictyostelium
Myosin-I Isozymes
Scott W. Crawley†, Janine Liburd†, Kristopher Shaw, Yoojin Jung,
Steven P. Smith and Graham P. Côté
From the Department of Biochemistry, Queen’s University, Kingston,
Ontario, Canada K7L 3N6
†These authors contributed equally to this work
Biochemistry, in press
Dictyostelium discoideum express seven single-headed myosin-I isozymes
(MyoA-MyoE and MyoK) that drive motile processes at the cell membrane.
The light chains for MyoA and MyoE were identified by expressing
Flag-tagged constructs consisting of the motor domain and the two IQ
motifs in the neck region in Dictyostelium. The MyoA and MyoE constructs
both co-purified with calmodulin. Isothermal titration calorimetry (ITC)
showed that apo-calmodulin bound to peptides corresponding to the MyoA
and MyoE IQ motifs with micromolar affinity. In the presence of calcium,
calmodulin cross-linked two IQ motif peptides, with one domain binding with
nanomolar affinity and the other with micromolar affinity. The IQ motifs were
required for the actin-activated MgATPase activity of MyoA but not MyoE;
however, neither myosin exhibited calcium-dependent activity. A
Flag-tagged construct consisting of the MyoC motor domain and the three
IQ motifs in the adjacent neck region bound a novel 8.6 kDa two EF-hand
protein named MlcC, for myosin light chain for MyoC. MlcC is most similar
to the C-terminal domain of calmodulin but does not bind calcium. ITC
studies showed that MlcC binds IQ1 and IQ2 but not IQ3 of MyoC. IQ3
contains a proline residue that may render it non-functional. Each
long-tailed Dictyostelium myosin-I has now been shown to have a unique
light chain (MyoB- MlcB, MyoC-MlcC and MyoD-MlcD), whereas the
short-tailed myosins-I, MyoA and MyoE, have the multi-functional
calmodulin as a light chain. The diversity in light chain composition is likely
to contribute to the distinct cellular functions of each myosin-I isozyme.
Submitted by Scott W. Crawley [[log in to unmask]]
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[End dictyNews, volume 36, number 17]
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