AFM force spectroscopy reveals how subtle structural differences affect the interaction strength between Candida...

Area of Science:

• Mycology
• Immunology
• Structural Biology

Background:

• Candida albicans is a common fungal pathogen in immunocompromised individuals.
• Interactions between Candida and immune receptors like DC-SIGN are crucial but poorly understood at a structural level.
• DC-SIGN recognizes mannan structures on Candida's cell wall, but the precise recognition mechanism remains unclear.

Purpose of the Study:

• To investigate the role of mannan structure variations in Candida albicans binding to DC-SIGN.
• To elucidate the molecular recognition mechanism between Candida mannan and DC-SIGN using advanced biophysical techniques.
• To quantify the binding affinity and energy associated with DC-SIGN-mannan interactions.

Main Methods:

• Utilized atomic force microscope-based dynamic force spectroscopy (DFS) on single Candida albicans cells.
• Analyzed the impact of N-mannan structure differences, specifically phosphomannan side chains, on DC-SIGN binding.
• Measured single-bond affinity and dissociation constants for tetrameric DC-SIGN interactions with Candida cells.

Main Results:

• Demonstrated that the presence or absence of a phosphomannan side chain on Candida's N-mannan influences DC-SIGN recognition.
• Showed that phosphomannan side chains contribute to the compliance of the Candida cell wall.
• Quantified a higher binding energy (1.6 kB T) and a strong single-bond affinity (~10.7 kB T) for DC-SIGN with wild-type Candida albicans, with a dissociation constant of 23 μM.

Conclusions:

• DC-SIGN specifically recognizes mannan patterns on Candida albicans with high affinity.
• Structural variations in Candida's mannan, particularly phosphomannan, significantly impact immune receptor binding.
• Understanding these interactions can inform the development of novel antifungal therapies targeting fungal carbohydrate recognition.