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Candida albicans binds human plasminogen: identification of eight plasminogen-binding proteins
Jonathan D Crowe1, Isla K Sievwright, Gillian C Auld
1Department of Molecular and Cell Biology, Institute of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, UK.
Abstract:
Several microbial pathogens augment their invasive potential by binding and activating human plasminogen to generate the proteolytic enzyme plasmin. Yeast cells and cell wall proteins (CWP) of the human pathogenic fungus Candida albicans bound plasminogen with a K(d) of 70 +/- 11 nM and 112 +/- 20 nM respectively. Bound plasminogen could be activated to plasmin by mammalian plasminogen activators; no C. albicans plasminogen activator was detected. Binding of plasminogen to CWP and whole cells was inhibited by epsilon ACA, indicating that binding was predominantly to lysine residues. Candida albicans mutant strains defective in protein glycosylation did not show altered plasminogen binding, suggesting that binding was not mediated via a surface lectin. Binding was sensitive to digestion by basic carboxypeptidase, implicating C-terminal lysine residues in binding. Proteomic analysis identified eight major plasminogen-binding proteins in isolated CWP. Five of these (phosphoglycerate mutase, alcohol dehydrogenase, thioredoxin peroxidase, catalase, transcription elongation factor) had C-terminal lysine residues and three (glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase and fructose bisphosphate aldolase) did not. Activation of plasminogen could potentially increase the capacity of this pathogenic fungus for tissue invasion and necrosis. Although surface-bound plasmin(ogen) degraded fibrin, no direct evidence for a role in invasion of endothelial matrix or in penetration and damage of endothelial cells was found.
Insights
The fungus Candida albicans binds human plasminogen to its cell wall proteins, potentially enhancing its invasive capabilities. This binding primarily involves lysine residues on the fungal proteins.
Area of Science:
- Microbiology
- Biochemistry
- Mycology
Background:
- Microbial pathogens utilize host plasminogen to generate plasmin, a proteolytic enzyme, thereby increasing invasiveness.
- Candida albicans is a human pathogenic fungus with significant implications for infectious diseases.
Purpose of the Study:
- To investigate the binding of human plasminogen to Candida albicans.
- To identify the mechanisms and proteins involved in plasminogen binding by C. albicans.
- To assess the functional consequences of plasminogen binding for fungal pathogenicity.
Main Methods:
- Quantification of plasminogen binding to C. albicans yeast cells and cell wall proteins (CWP) using dissociation constant (K(d)) measurements.
- Inhibition assays using epsilon-aminocaproic acid (epsilon-ACA) to identify binding residues.
- Enzymatic digestion studies with basic carboxypeptidase to probe C-terminal lysine involvement.
- Proteomic analysis to identify plasminogen-binding proteins within CWP.
- Functional assays to assess plasminogen activation and degradation of extracellular matrix components.
Main Results:
- C. albicans yeast cells and CWP exhibited significant plasminogen binding (K(d) of 70 +/- 11 nM and 112 +/- 20 nM, respectively).
- Binding was inhibited by epsilon-ACA and sensitive to basic carboxypeptidase, indicating a primary role for lysine residues.
- Proteomic analysis identified eight major plasminogen-binding proteins in CWP, some with and some without C-terminal lysine residues.
- Bound plasminogen could be activated by mammalian activators, but no C. albicans-specific activator was found.
- While bound plasmin(ogen) degraded fibrin, direct evidence for enhanced invasion or endothelial cell damage was not observed.
Conclusions:
- Candida albicans efficiently binds human plasminogen via its cell wall proteins, primarily through lysine residues.
- This interaction has the potential to enhance fungal tissue invasion and necrosis, although direct evidence in vitro was limited.
- The identified plasminogen-binding proteins offer targets for understanding and potentially disrupting C. albicans pathogenicity.