The PR-10 Protein Pru p 1 is an Endonuclease that Preferentially Cleaves Single-Stranded RNA

Pathogenesis-related class 10 (PR-10) proteins play a crucial role in plant defense by acting as ribonucleases. The specific mechanism of action and substrate specificity of these proteins have remained largely unexplored so far. In this study, we elucidate the enzymatic activity of Pru p 1, a PR-10 protein from peach. We demonstrate that this protein catalyzes the endonucleolytic backbone cleavage of RNA substrates into short oligonucleotides. Initial cleavage products, identified through kinetic analysis, can bind again, priming them for further degradation. NMR binding site mapping reveals that the large internal cavity of Pru p 1, which is characteristic for PR-10 proteins, serves as an anchoring site for single-stranded ribonucleotide chains. We propose a structure-based mechanistic model that accounts for the observed cleavage patterns and the inhibitory effect of zeatin, a nucleoside analog, on the ribonuclease activity of Pru p 1.