What is it about?

Protein mediated plant cell wall loosening is a natural process. It enables plant growth and improves cell wall accessibility for microorganisms that degrade cell walls. Although these proteins resemble enzymes, nature's catalysts, they have traditionally been viewed as non catalytic, acting by disrupting non covalent bonds that hold the many polymers in the plant cell wall together. Our findings challenge this view by providing direct evidence that a fungal expansin‑like protein can cleave one of these cell wall polymers, namely glucuronoxylan. Thus, cell wall loosening may be linked to enzyme action after all.

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Why is it important?

Our findings challenge the current paradigm that cell wall loosening proteins are non catalytic and open up new hypotheses, not only regarding plant growth but also regarding turnover of biomass in nature, such as fungal wood decay. Our results suggest that expansin related proteins may have a wider range of biochemical functions than previously assumed, with potential implications for plant science, biomass conversion, and biorefining.

Perspectives

This work was especially exciting for us because it revisits a textbook assumption in the expansin field. For years, the absence of detectable reaction products shaped how expansins were discussed and taught. Finding clear evidence of catalysis in a single domain expansin like protein felt like taking a first concrete step towards finally resolving a question many of us have long wondered about. We focused on this protein because it is strongly expressed at very early stages of brown rot fungal wood decay, a phase dominated by Fenton reaction based chemistry rather than classical enzymatic degradation. Several important questions remain, and we hope our work encourages the community to revisit the mechanisms of expansin catalyzed cell wall loosening, brown rot decay, and the application of these proteins in biorefining.

Aniko Varnai
Norges miljo- og biovitenskapelige universitet

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This page is a summary of: A single-domain expansin-like protein from Gloeophyllum trabeum able to cleave xylan, Proceedings of the National Academy of Sciences, January 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2528599123.
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