Pbx proteins in Cryptococcus neoformans cell wall remodeling and capsule assembly.

Felipe H Santiago-Tirado's picture
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TitlePbx proteins in Cryptococcus neoformans cell wall remodeling and capsule assembly.
Publication TypeJournal Article
Year of Publication2014
AuthorsKumar, P, Heiss, C, Santiago-Tirado, FH, Black, I, Azadi, P, Doering, TL
JournalEukaryot Cell
Volume13
Issue5
Pagination560-71
Date Published2014 May
ISSN1535-9786
KeywordsCarbohydrate Sequence, Cell Wall, Cryptococcosis, Cryptococcus neoformans, Fungal Capsules, Fungal Proteins, Humans, Molecular Sequence Data, Polysaccharides, Virulence Factors
Abstract

<p>The cryptococcal capsule is a critical virulence factor of an important pathogen, but little is known about how it is associated with the cell or released into the environment. Two mutants lacking PBX1 and PBX2 were found to shed reduced amounts of the capsule polysaccharide glucuronoxylomannan (GXM). Nuclear magnetic resonance, composition, and physical analyses showed that the shed material was of normal mass but was slightly enriched in xylose. In contrast to previous reports, this material contained no glucose. Notably, the capsule fibers of pbxΔ mutant cells grown under capsule-inducing conditions were present at a lower than usual density and were loosely attached to the cell wall. Mutant cell walls were also defective, as indicated by phenotypes including abnormal cell morphology, reduced mating filamentation, and altered cell integrity. All observed phenotypes were shared between the two mutants and exacerbated in a double mutant. Consistent with a role in surface glycan synthesis, the Pbx proteins localized to detergent-resistant membrane domains. These results, together with the sequence motifs in the Pbx proteins, suggest that Pbx1 and Pbx2 are redundant proteins that act in remodeling the cell wall to maintain normal cell morphology and precursor availability for other glycan synthetic processes. Their absence results in aberrant cell wall growth and metabolic imbalance, which together impact cell wall and capsule synthesis, cell morphology, and capsule association. The surface changes also lead to increased engulfment by host phagocytes, consistent with the lack of virulence of pbx mutants in animal models. </p>

DOI10.1128/EC.00290-13
Alternate JournalEukaryotic Cell
PubMed ID24585882
PubMed Central IDPMC4060484
Grant ListR01 AI078795 / AI / NIAID NIH HHS / United States
GM098791 / GM / NIGMS NIH HHS / United States
R01 AI78795 / AI / NIAID NIH HHS / United States
R01 GM071007 / GM / NIGMS NIH HHS / United States
U54 GM062116 / GM / NIGMS NIH HHS / United States
GM062116 / GM / NIGMS NIH HHS / United States
R24 GM098791 / GM / NIGMS NIH HHS / United States