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Published on: July 28, 2016
Candidacidal activity of myeloperoxidase: characterization of myeloperoxidase-yeast complex formation
1Department of Microbiology, University of Minnesota, Minneapolis 55455.
Abstract:
We have previously demonstrated the ability of human neutrophil myeloperoxidase to bind to cell wall mannan polysaccharide isolated from Candida albicans. This binding capacity provides for association of the enzyme with target yeast which is essential for efficient candidacidal activity. In this report, we further consider the role of the mannan-binding property of myeloperoxidase in the candidacidal activity of the enzyme. Solubilized mannan antagonizes binding of the enzyme to yeast, suggesting that mannan may be a primary component of the fungal cell wall which serves as a target for binding of myeloperoxidase. Myeloperoxidase is shown to form complexes with both solubilized mannan and Candida yeast, with Kds of 0.97 x 10(-5) M and 1.2 x 10(-5) M, respectively. The interaction between myeloperoxidase and mannan does not allow the enzyme to readily dissociate from the surface of target yeast. As a result, the enzyme may be unable to dissociate from dead yeast to become available for binding to additional fungal targets.
Insights
Human neutrophil myeloperoxidase binds to Candida albicans mannan, crucial for killing yeast. However, this binding can prevent myeloperoxidase from targeting new yeast cells.
Area of Science:
- Immunology
- Microbiology
- Biochemistry
Background:
- Human neutrophil myeloperoxidase (MPO) binds to mannan polysaccharide on Candida albicans.
- This interaction is essential for effective candidacidal activity.
- The study investigates the role of MPO's mannan-binding property in its fungicidal function.
Purpose of the Study:
- To elucidate the mechanism by which myeloperoxidase interacts with Candida albicans.
- To determine the significance of mannan as a binding target for myeloperoxidase.
- To assess the impact of MPO-mannan interaction on the enzyme's ability to target multiple yeast cells.
Main Methods:
- Investigating the binding of myeloperoxidase to isolated mannan polysaccharide from Candida albicans.
- Assessing the effect of solubilized mannan on MPO-yeast binding.
- Quantifying the binding affinity (Kd) of MPO to solubilized mannan and Candida yeast.
- Observing the dissociation kinetics of MPO from yeast cells.
Main Results:
- Solubilized mannan inhibits the binding of myeloperoxidase to yeast, indicating mannan is a key MPO target on the fungal cell wall.
- Myeloperoxidase forms stable complexes with both solubilized mannan (Kd = 0.97 x 10^-5 M) and Candida yeast (Kd = 1.2 x 10^-5 M).
- The strong interaction between MPO and mannan results in poor dissociation of the enzyme from dead yeast cells.
Conclusions:
- Mannan is a critical component of the Candida albicans cell wall that mediates the binding of human neutrophil myeloperoxidase.
- The tight binding of MPO to mannan may limit its availability to engage new fungal targets after initial binding.
- This binding characteristic could influence the overall efficiency and duration of myeloperoxidase-mediated candidacidal activity.
