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dictyNews Volume 24 Number 01
Dicty News
Electronic Edition
Volume 24, number 1
January 14, 2005
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.
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Abstracts
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A DICTYOSTELIUM MUTANT WITH REDUCED LYSOZYME LEVELS COMPENSATES BY
INCREASED PHAGOCYTIC ACTIVITY
Iris Mueller#, Ninon Subert~, Heike Otto#, Rosa Herbst¤, Harald Ruehling#,
Markus Maniak# @, and Matthias Leippe&
The Journal of Biological Chemistry, in press
Lysozymes are bacteria-degrading enzymes and play a major role in the
immune defense of animals. In free-living protozoa, lysozyme-like proteins
are involved in the digestion of phagocytosed bacteria. Here, we purified
a protein with lysozyme activity from Dictyostelium amoebae, which
constitutes the founding member a novel class of lysozymes. By tagging the
protein with GFP1 or the myc epitope, a new type of lysozyme containing
vesicle was identified that was devoid of other known lysosomal enzymes.
The most highly expressed isoform, encoded by the alyA gene, was knocked
out by homologous recombination. The mutant cells had greatly reduced
enzymatic activity and grew inefficiently when bacteria were the sole food
source. Over time, the mutant gained the ability to internalize bacteria
more efficiently, so that the defect in digestion was compensated by
increased uptake of food particles.
Submitted by: Markus Maniak [maniak@uni-kassel.de]
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Kinetic analysis of a Golgi UDP-GlcNAc:polypeptide-Thr/Ser
N-acetyl-alpha-glucosaminyltransferase from Dictyostelium
Altan Ercan and Christopher M. West
Department of Biochemistry and Molecular Biology, 940 Stanton L. Young Blvd.,
BMSB 937, University of Oklahoma Health Sciences Center, Oklahoma City,
Oklahoma 73104 USA; telephone: 405-271-2227 x1247; Fax 405-271-3139;
email: Cwest2@ouhsc.edu
Glycobiology, in press
Mucin-type O-glycosylation in Dictyostelium is initiated in the Golgi by a
UDP-GlcNAc:polypeptide-Thr/Ser N-acetyl-alpha-glucosaminyltransferase
(Dd-pp alphaGlcNAcT2) whose sequence is distantly related to the sequences
of animal polypeptide-Thr/Ser N-acetyl-alpha-galactosaminyltransferases such
as murine Mm-pp alphaGalNAcT1. To evaluate the significance of this
similarity, highly purified Dd-pp alphaGlcNAcT2 was assayed using synthetic
peptides derived from known substrates. Dd-pp alphaGlcNAcT2 strongly prefers
UDP-GlcNAc over UDP-GalNAc, preferentially modifies the central region of
the peptide, and modifies Ser- in addition to Thr-residues. Initial velocity
measurements performed over a matrix of UDP-GlcNAc donor and peptide
acceptor concentrations indicate that the substrates bind to the enzyme in
ordered fashion before the chemical conversion. Substrate inhibition exerted
by a second peptide, and the pattern of product inhibition exerted by UDP,
suggest that UDP-GlcNAc binds first and the peptide binds second, consistent
with data reported for Mm-pp alphaGalNAcT1. Two selective competitive
inhibitors of Mm-pp alphaGalNAcT1, retrieved from a screen of neutral-charge
uridine derivatives, also inhibit Dd-pp alphaGlcNAcT1 competitively with
only slightly less efficacy. Inhibition is specific for Dd-pp alphaGlcNAcT2
relative to two other Dictyostelium retaining glycosyltransferases. These
data support a phylogenetic model in which the alphaGlcNAcT function in
unicellular eukaryotes converted to an alphaGalNAcT function in the metazoan
ortholog while conserving a similar reaction mechanism and active site
architecture.
Submitted by: Chris West [Cwest2@ouhsc.edu]
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[End Dicty News, volume 24, number 1] 
