dictyNews
Electronic Edition
Volume 45, number 14
MAY 17, 2019
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Abstracts
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Social amoebae establish a protective interface with their bacterial
associates by lectin agglutination
Timothy Farinholt, Christopher Dinh, & Adam Kuspa
Verna and Marrs McLean Department of Biochemistry and
Molecular Biology
Science Advances, accepted
Animals and amoebae share cellular features for immune defense
that they use to kill bacteria such as phagocytosis and DNA-based
extracellular traps. Whether they also share tissue-level barriers to
reduce direct exposure to bacteria is not known. We have explored
this question in the social amoebae Dictyostelium discoideum that forms
plaques on thick lawns of food bacteria that expand as amoebae divide
and bacteria are consumed. Here we show that CadA, a cell adhesion
protein that functions in D. discoideum multicellular development, is also
a bacterial agglutinin that forms a protective interface at the plaque edge
to limit the exposure of vegetative amoebae to bacteria. This interface is
important for amoebal survival when bacteria-to-amoebae ratios are high,
optimizes amoebal feeding behavior and protects amoebae from oxidative
stress. Lectins also control bacterial access to the gut epithelium of
mammals to limit inflammatory processes, so this appears to be common
strategy of antibacterial defense across a broad spectrum of eukaryotic
phylogeny.
submitted by: Adam Kuspa [[log in to unmask]]
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Antimicrobial activities of Dictyostelium differentiation-inducing factors
and their derivatives
Yuzuru Kubohara *, Yoshiko Shiratsuchi, Hirotaka Ishigaki, Katsunori
Takahashi, Yoshiteru Oshima, Haruhisa Kikuchi
Biomolecules, in press
At the end of its life cycle, the cellular slime mold Dictyostelium discoideum
forms a fruiting body consisting of spores and a multicellular stalk. Originally,
the chlorinated alkylphenone differentiation-inducing factors (DIFs) -1 and
-3 were isolated as stalk cell inducers in D. discoideum. Later, DIFs and their
derivatives were shown to possess several biologic activities including
antitumor and anti-Trypanosoma properties. In this study, we examined the
antibacterial activities of approximately 30 DIF derivatives by using several
bacterial species. Several of the DIF derivatives strongly suppressed the
growth of the Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis,
and Enterococcus faecalis and E. faecium, at minimum inhibitory
concentrations (MICs) in the submicromolar to low-micromolar range. In
contrast, none of the DIF derivatives evaluated had any noteworthy effect on
the growth of the Gram-negative bacterium Escherichia coli (MIC, >100
microM). Most importantly, several of the DIF derivatives strongly inhibited the
growth of methicillin-resistant S. aureus and vancomycin-resistant E. faecalis
and E. faecium. Transmission electron microscopy revealed that treatment with
DIF derivatives led to the formation of distinct multilayered structures consisting
of cell wall or plasma membrane in S. aureus. The present results suggest that
DIF derivatives are good lead compounds for developing novel antimicrobials.
submitted by: Yuzuru Kubohara [[log in to unmask]]
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Nucleocytoplasmic O-glycosylation in protists
Christopher M. West1,2,3,4 and Hyun W. Kim1
1Department of Biochemistry & Molecular Biology,
2Center for Tropical and Emerging Global Diseases, and the
3Complex Carbohydrate Research Center, University of Georgia,
Athens, GA 30602 USA
Current Opinion in Structural Biology (2019), in press
Highlights
• Nucleocytoplasmic O-GlcNAc is replaced by O-fucose in many protists
• A complex cytoplasmic O-glycosylation pathway is conserved across the protist
kingdom
• The covalently bound sugars represent novel mechanisms to modulate local
order in proteins
• Nucleocytoplasmic glycoregulation may be important for environmental sensing
• The parasite Toxoplasma gondii relies on nucleocytoplasmic glycosylation for
optimal growth
O-glycosylation is an increasingly recognized modification of intracellular
proteins in all kingdoms of life, and its occurrence in protists has been
investigated to understand its evolution and its roles in the virulence of
unicellular pathogens. We focus here on two kinds of glycoregulation found
in unicellular eukaryotes: one is a simple O-fucose modification of dozens
if not hundreds of Ser/Thr-rich proteins, and the other a complex
pentasaccharide devoted to a single protein associated with oxygen sensing
and the assembly of polyubiquitin chains. These modifications are not
required for life but contingently modullate biological processes in the social
amoeba Dictyostelium and the human pathogen Toxoplasma gondii, and
likely occur in diverse unicellular protists. O-glycosylation that is co-localized
in the cytoplasm allows for glycoregulation over the entire life of the protein,
contrary to the secretory pathway where glycosylation usually occurs before
its delivery to its site of function. Here we interpret cellular roles of
nucleocytoplasmic glycans in terms of current evidence for their effects on
the conformation and dynamics of protist proteins, to serve as a guide for
future studies to examine their broader significance.
submitted by: Chris West [[log in to unmask]]
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[End dictyNews, volume 45, number 14]
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