Solution NMR Structures of Pyrenophora tritici-repentis ToxB and Its Inactive Homolog Reveal Potential Determinants of Toxin Activity

摘要: Pyrenophora tritici-repentis Ptr ToxB (ToxB) is a proteinaceous host-selective toxin produced by (P. tritici-repentis), plant pathogenic fungus that causes the disease tan spot of wheat. One feature distinguishes from other toxins it has naturally occurring homologs in non-pathogenic P. isolates lack toxic activity. There are no high-resolution structures for any homologs, or protein with >30% sequence identity, and therefore what underlies activity remains an open question. Here, we present NMR its inactive homolog toxb. Both proteins adopt β-sandwich fold comprising three strands each half bridged together two disulfide bonds. The toxb, however, shows higher flexibility localized to sequence-divergent half. absence attributed more structure vicinity one bond, flexibility, residue differences exposed loop likely impacts interaction putative targets. We propose regulated perturbations active site changes dynamics distant Interestingly, new identify AvrPiz-t, secreted avirulence rice blast fungus, as structural ToxB. This homology suggests fungal involved either susceptibility such resistance AvrPiz-t may have common evolutionary origin.