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Chemoenzymatic Probes Reveal Peptidoglycan Recognition and Uptake Mechanisms in Candida albicans
Lanxin Li1, Allan Wee Ren Ng1, Christopher Adamson1
1Division of Chemistry and Biological Chemistry (CBC), School of Physical and Mathematical Sciences (SPMS), Nanyang Technological University, 21 Nanyang Link, S637371 Singapore.
Abstract:
Candida albicans, the major fungal pathogen in humans, is under the strong influence of bacterial peptidoglycan fragments to undergo the yeast-to-hyphae transition, a key virulent step in C. albicans pathogenesis and infections. However, due to the synthetic difficulties of obtaining peptidoglycan fragments for biological studies, mechanistic details of how C. albicans recognizes and uptakes these peptidoglycan fragments have not been well elucidated. Notably, previous works have solely focused on the synthetic peptidoglycan ligand, muramyl dipeptide (MDP), despite its poor hyphal-inducing activity in C. albicans. In this work, we isolated and purified natural peptidoglycan fragments via enzymatic degradation of bacteria cell wall sacculi and chemoenzymatically installed a series of functional d-amino acids into the natural muropeptide, creating peptidoglycan probes that bear photoaffinity, bio-orthogonal, or fluorescent functionality. Using these chemoenzymatic peptidoglycan probes, we established that natural peptidoglycan fragments, which are potent hyphal-inducers, interact with the C. albicans Cyr1 sensor protein in the in-gel fluorescence assay as well as in in vitro pulldown studies. Moreover, we established that bacterial peptidoglycan probes enter C. albicans cells via an energy-dependent endocytic process.
Insights
Bacterial peptidoglycan fragments strongly induce hyphal growth in Candida albicans. Researchers developed novel probes to show these fragments bind to the Cyr1 protein and enter cells via endocytosis.
Area of Science:
- Microbiology
- Mycology
- Biochemistry
Background:
- Candida albicans, a major human fungal pathogen, utilizes yeast-to-hyphae transition for pathogenesis.
- Bacterial peptidoglycan fragments are known to influence this transition, but mechanisms of recognition and uptake remain unclear.
- Previous studies focused on synthetic muramyl dipeptide (MDP), which has weak hyphal-inducing activity.
Purpose of the Study:
- To elucidate the mechanisms by which Candida albicans recognizes and internalizes bacterial peptidoglycan fragments.
- To develop novel peptidoglycan probes for studying these interactions.
- To identify the specific sensor protein involved in peptidoglycan recognition.
Main Methods:
- Isolation and purification of natural peptidoglycan fragments from bacterial cell walls.
- Chemoenzymatic installation of functional groups (photoaffinity, bio-orthogonal, fluorescent) onto natural muropeptides.
- In-gel fluorescence assays and in vitro pulldown studies using peptidoglycan probes.
- Investigation of cellular uptake mechanisms.
Main Results:
- Natural peptidoglycan fragments are potent inducers of hyphal growth in C. albicans.
- These fragments interact with the Cyr1 sensor protein in C. albicans.
- Bacterial peptidoglycan probes are internalized by C. albicans cells through an energy-dependent endocytic pathway.
Conclusions:
- Natural peptidoglycan fragments, not just synthetic ones like MDP, are key inducers of C. albicans hyphal transition.
- The Cyr1 protein is a crucial sensor for these bacterial fragments.
- C. albicans actively internalizes peptidoglycan fragments via endocytosis, suggesting a role in pathogenesis.
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