InterPro domain: IPR002885

This entry represents the PPR repeat.

Pentatricopeptide repeat (PPR) proteins are characterised by tandem repeats of a degenerate 35 amino acid motif [ 1 ]. PPR proteins are sequence-specific RNA-binding proteins that are involved in multiple aspects of RNA metabolism [ 2 , 3 ]. They can bind a diversity of sequences that confers the variability in its functions [ 4 ]. Most have roles in mitochondria or plastids [ 5 ]. PPR repeats were discovered while screening Arabidopsis proteins for those predicted to be targeted to mitochondria or chloroplast [ 6 , 6 ]. Some of these proteins have been shown to play a role in post-transcriptional processes within organelles [ 7 , 8 ]. Plant genomes have between one hundred to five hundred PPR genes per genome whereas non-plant genomes encode two to six PPR proteins.

The plant PPR protein family has been divided in two subfamilies on the basis of their motif content and organisation [ 9 , 9 ].

The crystal structure of maize chloroplast PPR10 has been reported. The nineteen repeats of PPR10 are assembled into a right-handed superhelical spiral. PPR10 forms a homodimer and exhibits considerable conformational changes upon binding to its ssRNA target, with six nucleotides being specifically recognized by six corresponding PPR10 repeats [ 10 ].

1. The PPR motif - a TPR-related motif prevalent in plant organellar proteins. Trends Biochem. Sci. 25, 46-7
2. Pentatricopeptide repeat (PPR) proteins as sequence-specificity factors in post-transcriptional processes in organelles. Biochem. Soc. Trans. 35, 1643-7
3. Mechanistic insight into pentatricopeptide repeat proteins as sequence-specific RNA-binding proteins for organellar RNAs in plants. Plant Cell Physiol. 53, 1171-9
4. Unexpected functional versatility of the pentatricopeptide repeat proteins PGR3, PPR5 and PPR10. Nucleic Acids Res. 46, 10448-10459
5. Chloroplast RNA-binding and pentatricopeptide repeat proteins. Biochem. Soc. Trans. 32, 571-4
6. Genome-wide analysis of Arabidopsis pentatricopeptide repeat proteins reveals their essential role in organelle biogenesis. Plant Cell 16, 2089-103
7. HCF152, an Arabidopsis RNA binding pentatricopeptide repeat protein involved in the processing of chloroplast psbB-psbT-psbH-petB-petD RNAs. Plant Cell 15, 1480-95
8. LRP130, a pentatricopeptide motif protein with a noncanonical RNA-binding domain, is bound in vivo to mitochondrial and nuclear RNAs. Mol. Cell. Biol. 23, 4972-82
9. Pentatricopeptide repeat proteins and their emerging roles in plants. Plant Physiol. Biochem. 45, 521-34
10. Structural basis for the modular recognition of single-stranded RNA by PPR proteins. Nature 504, 168-71