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The glycolipid flocculosin-A from the fungus Anthracocystis flocculosa, or how to deal with cotton-wool-like crystals

Summary

Scientists successfully determined the three-dimensional structure of flocculosin-A, a powerful antifungal compound produced by a fungus called Anthracocystis flocculosa. The main challenge was that the compound naturally forms very thin, needle-like crystals unsuitable for analysis. By using a special cooling and heating cycle, researchers were able to grow better crystals and use X-ray diffraction to reveal the compound’s complete molecular structure, which contains a sugar backbone connected to two fatty acid chains with specific arrangements.

Background

Flocculosin-A is a major glycolipid antifungal metabolite secreted by the basidiomycetous fungus Anthracocystis flocculosa (formerly Pseudozyma flocculosa). This compound has broad-spectrum antimicrobial properties and potential applications as a source of ω-hydroxy fatty acids and surfactant molecules. However, the compound presents significant crystallization challenges, forming long, soft cotton-wool-like needle crystals unsuitable for structural analysis.

Objective

To optimize crystal growth of flocculosin-A and determine its three-dimensional crystal structure including the absolute configuration of its chiral centers using X-ray crystallography. The research aimed to overcome the challenge of poor crystallinity and unfavorable needle-like morphology.

Results

The crystal structure of flocculosin-A was successfully solved, revealing a cellobiose disaccharide core linked to hydroxy-palmitoic acid and hydroxy-caproic acid chains. The structure contains three chiral centers in the lipid chains with determinable absolute configurations. The crystal structure retained one ordered water molecule and one disordered ethanol molecule in the crystal packing.

Conclusion

By adopting a specialized cyclic temperature variation crystallization protocol, exploitable crystals of flocculosin-A were obtained for the first time. The structure determination enables evaluation of structure-activity relationships and supports further research into antifungal properties and potential applications of flocculosin and its analogs.
  • Published in:Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials,
  • Study Type:Structural Study,
  • Source: 10.1107/S2052520625008583, PMID: 41201986
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