Copy Link
Add to Bookmark
Report
dictyNews Volume 21 Number 15
Dicty News
Electronic Edition
Volume 21, number 15
November 7, 2003
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
=============
Initiation of Mucin-type O-Glycosylation in Dictyostelium is Homologous
to the Corresponding Step in Animals and is Important for Spore
Coat Function*
Fei Wang½, Talibah Metcalf½¦, Hanke van der Wel½¦, and
Christopher M. West½¦
From the ½Department of Anatomy & Cell Biology, College of Medicine,
1600 SW Archer Road, University of Florida, Gainesville, FL 32610-0235,
and the ¦Department of Biochemistry & Molecular Biology, University of
Oklahoma Health Sciences Center, Oklahoma City, OK 73104 USA
J. Biol. Chem., in press
Like animal cells, many unicellular eukaryotes modify mucin-like domains
of secretory proteins with multiple O-linked glycans. Unlike animal
mucin-type glycans, those of some microbial eukaryotes are initiated by
alpha-linked GlcNAc rather than alpha-GalNAc. Based on sequence similarity
to a recently cloned soluble polypeptide hydroxyproline GlcNAc-transferase
that modifies Skp1 in the cytoplasm of the social amoeba Dictyostelium, we
have identified an enzyme, pp alpha-GlcNAc-T2, that attaches GlcNAc to
numerous secretory proteins in this organism. Unlike the Skp1
GlcNAc-transferase, pp alpha-GlcNAc-T2 is predicted to be a type 2
transmembrane protein. A highly purified, soluble, recombinant fragment of
pp alpha-GlcNAc-T2 efficiently transfers GlcNAc from UDP-GlcNAc to synthetic
peptides corresponding to mucin-like domains in two proteins which traverse
the secretory pathway. pp alpha-GlcNAc-T2 is required for addition of GlcNAc
to peptides in cell extracts and to the proteins in vivo. Mass spectrometry
and Edman degradation analyses show that pp alpha-GlcNAc-T2 attaches GlcNAc
in alpha-linkage to the Thr-residues of all the synthetic mucin-repeats.
pp alpha-GlcNAc-T2 is encoded by the previously described modB-locus defined
by chemical mutagenesis, based on sequence analysis and complementation
studies. This finding establishes that the many phenotypes of modB-mutants,
including a permeability defect in the spore coat, can now be ascribed to
defects in mucin-type O-glycosylation. A comparison of the sequences of
pp alpha-GlcNAc-T2 and the animal pp alpha-GalNAc-transferases reveals an
ancient common ancestry indicating that, despite the different
N-acetylhexosamines involved, the enzymes share a common mechanism of action. Ê
Submitted by: Chris West [Christopher-West@ouhsc.edu]
-----------------------------------------------------------------------------
Involvement of the AP-1 adaptor complex in early steps of phagocytosis and
macropinocytosis
Yaya Lefkir, Marilyne Malbouyres, Daniel Gotthardt, Adrian Ozinsky, Sophie
Cornillon, Franz Bruckert, Alan A. Aderem, Thierry Soldati, Pierre Cosson,
and Franois Letourneur
MBC, in press
The best described function of the adaptor complex-1 (AP-1) is to participate
in the budding of clathrin-coated vesicles from the trans-Golgi network and
endosomes. Here we show that AP-1 is also localized to phagocytic cups in
murine macrophages as well as in Dictyostelium amoebae. AP-1 is recruited to
phagosomal membranes at this early stage of phagosome formation and rapidly
dissociates from maturing phagosomes. To establish the role of AP-1 in
phagocytosis, we made used of Dictyostelium mutant cells (apm1- cells)
disrupted for AP-1 medium chain. In this mutant, phagocytosis drops by 60%
indicating that AP-1 is necessary for efficient phagocytosis. Furthermore,
phagocytosis in apm1- cells is more affected for large rather than small
particles and cells exhibiting incomplete engulfment are then often observed.
This suggests that AP-1 could participate in the extension of the phagocytic
cup. Interestingly, macropinocytosis, a process dedicated to fluid-phase
endocytosis and related to phagocytosis, is also impaired in apm1- cells.
In summary, our data suggest a new role of AP-1 at an early stage of
phagosome and macropinosome formation.
Submitted by: Francois Letourneur [f.letourneur@ibcp.fr]
-----------------------------------------------------------------------------
Proteomics opens doors to the mechanisms of developmentally regulated
secretion
Stephen Alexander*, Supriya Srinivasan+ and Hannah Alexander*
*Division of Biological Sciences, University of Missouri, Columbia,
MO 65211-7400
+Gladstone Institute of Cardiovascular Disease, University of
California-San Francisco, San Francisco, CA 94141
Molecular and Cellular Proteomics, in press.
The program of multicellular development in Dictyostelium discoideum
culminates with the assembly of a rugged, environmentally resistant spore
coat around each spore cell. After synthesis, the proteins that will
constitute the coat are stored in prespore vesicles (PSVs) until an
unknown developmental signal triggers the PSVs to move to the cell surface
where they fuse with the plasma membrane and secrete their cargo by
exocytosis. These events occur synchronously in 80% of the cells in each
developing multicellular aggregate, and thus the system offers a unique
opportunity to study the developmental regulation of protein secretion in
situ. Proteomic analysis of purified PSVs identified many of the constituent
proteins, which in turn has lead to novel hypotheses and new experimental
avenues regarding the molecular mechanisms regulating secretion from the PSVs.
Submitted by: Hannah Alexander [AlexanderH@missouri.edu]
===============================================================================
[End Dicty News, volume 21, number 15]
