A peptide hidden inside a fungal protein tells a plant pathogen it has entered its host

Summary. Researchers at Heinrich Heine University Düsseldorf in Germany, working with colleagues at the University of Groningen, the University of Göttingen, NC State University and Imperial College London, reported in Nature Communications, published online on 9 October, a receptor system that lets the corn smut fungus Ustilago maydis detect that it has entered plant tissue. During infection the fungus secretes a protein called Pit2. Cysteine proteases in the space between the plant's cells cut Pit2 and release a peptide that was hidden within the protein's core. That peptide activates Gpe1, a fungal G-protein coupled receptor (GPCR), which promotes fungal proliferation after the fungus has first penetrated its host.

Research context (RUO). GPCRs share a seven-transmembrane architecture and are well characterised in mammals, but their fungal counterparts remain poorly understood, the authors note. The team solved the crystal structure of Pit2 and modelled the complex formed by Gpe1 and the Pit2-derived peptide. Structure-guided mutations that disrupt this interaction lowered fungal virulence, supporting the proposed mechanism. The Gpe1 and Pit2 pair is conserved in related fungal species, with co-evolutionary signatures that appear to preserve the match between receptor and ligand. The authors also describe mechanistic similarities to mammalian receptors, which they suggest point to an evolutionary link between fungal and mammalian GPCRs. The work concerns a plant pathogen and involves no animal or human data. For peptide researchers it is a clear example of a protease releasing an active peptide ligand from a larger precursor protein, studied with structural and mutational methods.