Structures of pentatricopeptide repeat proteins.

Pentatricopeptide repeat (PPR) proteins constitute the largest family of RNA-binding proteins in land plants, playing crucial roles in organellar gene expression through sequence-specific RNA recognition. Including the first PPR crystal structure in 2013, 30 PPR and 83 ribosomal PPR crystal or cryo-EM structures have been deposited in the Protein Data Bank, encompassing both native and designer proteins in apo and RNA-bound states. This comprehensive survey catalogues all PPR crystal structures, analysing their crystallographic properties, structural features and contributions to understanding PPR function. Key insights include the elucidation of the PPR recognition code, the characterization of dramatic conformational changes upon RNA binding and the structural basis for the modular architecture that enables programmable RNA targeting. Designer PPR structures have validated and extended principles derived from native proteins, demonstrating their utility as synthetic biology tools. This structural catalogue provides crystallographers and plant biologists with a comprehensive resource for understanding PPR protein architecture and function.