Copy Link
Add to Bookmark
Report
dictyNews Volume 23 Number 19
Dicty News
Electronic Edition
Volume 23, number 19
December 17, 2004
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
=============
Abstracts
=============
Changes in Mg2+-Ion Concentration and Heavy Chain Phosphorylation
Regulate the Motor Activity of a Class-I Myosin
Setsuko Fujita-Becker, Ulrike Dürrwang§, Muriel Erent, Richard J. Clark,
Michael A. Geeves, and Dietmar J. Manstein
Institute for Biophysical Chemistry, OE 4350, Hannover Medical School,
Carl-Neuberg-Straße 1, D-30623 Hannover, Germany and Department of
Biosciences, University of Kent, Canterbury CT2 7NJ, United Kingdom
Journal of Biological Chemistry, in press
Class-I myosins are single-headed motor proteins, implicated in various
motile processes including organelle translocation, ion-channel gating, and
cytoskeleton reorganization. Dictyostelium discoideum myosin-ID belongs to
subclass-1alpha, whose members are thought to be tuned for rapid sliding. The
direct analysis of myosin-ID motor activity is made possible by the
production of single polypeptide constructs carrying an artificial lever arm.
Using these constructs, we show that the motor activity of myosin-ID is
activated 80-fold by phosphorylation at the TEDS-site. TEDS-site
phosphorylation acts by stabilizing the actomyosin complex and increasing the
coupling between actin-binding and the release of hydrolysis products. A
surprising effect of Mg2+-ions on in vitro motility was discovered. Changes
in the level of free Mg2+-ions, within the physiological range, are shown to
modulate motor activity by inhibiting ADP-release. Our results indicate that
higher concentrations of free Mg2+-ions stabilise the tension-bearing
A.M.ADP state and shift the system from the production of rapid movement
towards the generation of tension.
Submitted by: Dietmar Manstein [manstein@bpc.mh-hannover.de]
-----------------------------------------------------------------------------
Constitutively active G protein-coupled receptor mutants block
Dictyostelium development
Minghang Zhang, Mousumi Goswami, and Dale Hereld
Department of Microbiology and Molecular Genetics, The University of Texas
Medical School at Houston, Houston, Texas 77030, USA
Molecular Biology of the Cell, in press
cAR1, a G protein-coupled receptor (GPCR) for cAMP, is required for the
multicellular development of Dictyostelium. The activation of multiple
pathways by cAR1 is transient due to poorly defined adaptation mechanisms.
To investigate this, we used a genetic screen for impaired development to
isolate four dominant-negative cAR1 mutants, designated DN1-4. The mutant
receptors inhibit multiple cAR1-mediated responses known to undergo
adaptation. Reduced in vitro adenylyl cyclase activation by GTPgammaS
suggests that they cause constitutive adaptation of this and perhaps other
pathways. In addition, the DN mutants are constitutively phosphorylated,
which normally requires cAMP binding, and possess cAMP affinities that are
~100-fold higher than that of wild-type cAR1. Two independent activating
mutations, L100H and I104N, were identified. These residues occupy
adjacent positions near the cytoplasmic end of the receptor's third
transmembrane helix and correspond to the (E/D)RY motif of numerous
mammalian GPCRs, which is believed to regulate their activation. Taken
together, these findings suggest that the DN mutants are constitutively
activated and block development by turning on natural adaptation
mechanisms.
Submitted by: Dale Hereld [dhereld@uth.tmc.edu]
-----------------------------------------------------------------------------
Cyclic AMP Receptors of Dictyostelium
Dale Hereld1 and Peter N. Devreotes2
1The University of Texas Health Science Center at Houston and 2The Johns
Hopkins University
In "Encyclopedia of Biological Chemistry" (W.J. Lennarz & M.D. Lane,
eds.), Elsevier, Oxford, in press
When confronted with starvation, the social amoeba Dictyostelium
discoideum survives by undergoing multicellular development and
sporulation. The coordination of these processes is achieved in part
through intercellular communication using secreted adenosine 3',5'-cyclic
monophosphate (cAMP) and a family of cell-surface cAMP receptors (cARs).
The cARs are examples of G protein-coupled receptors (GPCRs), which enable
eukaryotic cells in general to sense and respond to a wide array of
environmental and hormonal signals ranging from single photons to large
glycoprotein hormones. Due to their involvement in diverse physiological
processes, GPCR-targeted drugs are frequently employed in medicine to
treat many common conditions including inflammation, hypertension, heart
failure, and neurologic and psychiatric disorders. Because GPCRs and the
pathways they regulate are conserved in virtually all eukaryotes examined
to date, genetically tractable microbes such as Dictyostelium have
contributed significantly to our understanding of GPCR function and
regulation.
Submitted by: Dale Hereld [dhereld@uth.tmc.edu]
-----------------------------------------------------------------------------
Dd-Alix, a conserved endosome-associated protein, controls Dictyostelium
development
Sara Mattei§, W. Jonathan Ryves+, Béatrice Blot*, Rémy Sadoul*, Adrian J.
Harwood+, Michel Satre§, Gérard Klein§ and Laurence Aubry§
§Laboratoire de Biochimie et Biophysique des Systèmes Intégrés (UMR 5092
CNRS-CEA-UJF), DRDC, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble
Cedex 9, France; +MRC Laboratory for Molecular Cell Biology, University
College London, London WC1E 6BT, UK; *Laboratoire Neurodégénérescence
et Plasticité (EMI 0108 INSERM-UJF), CHU-Grenoble -BP 217, 38043 Grenoble
Cedex 9, France
accepted for publication in Developmental Biology
We have characterized the Dictyostelium homolog of the mammalian protein
Alix. Dd-Alix is encoded by a single gene and is expressed during
vegetative growth and multicellular development. We showed that the alx
null strain fails to complete its developmental program. Past the tight
aggregate stage, morphogenesis is impaired, leading to markedly aberrant
structures containing vacuolated and undifferentiated cells but no mature
spores. The developmental defect is cell-autonomous as most cells remain
of the PstB type even when mixed with wild-type cells. Complementation
analysis with different Alix constructs allowed the identification of a
101-residue stretch containing a coiled-coil domain essential for Alix
function. In addition, we showed that the protein associates in part with
vesicular structures and that its distribution on a Percoll gradient
overlaps that of the endocytic marker Vamp7. Dd-Alix also co-localizes
with Dd-Vps32. In view of our data, and given the role of Vps32 proteins
in membrane protein sorting and multivesicular body formation in yeast and
mammals, we hypothesize that the developmental defects of the alx null
strain result from abnormal trafficking of cell-surface receptors.
Submitted by: Laurence Aubry [laubry@cea.fr]
==============================================================================
[End Dicty News, volume 23, number 19] 
