Identification and characterization of peptides that bind the PPIase domain of Parvulin17.

Peptidyl-prolyl cis-trans isomerases (PPIases) are the enzymes that increase the rate of isomerization of the peptide bond N-terminal to the proline substrate. Par14 and its isoform Par17 belong to the Parvulin family of PPIases. Par14 can bind AT-rich double-stranded DNA and was shown to be part of the pre-ribosomal ribonucleoprotein (pre-rRNP) complexes, where it functions as an RNA processing factor that is involved in ribosome biogenesis. Its longer isoform Par17 is expressed only in cells of hominids, where it is targeted to the mitochondria. To find binding partners (peptides or proteins) for Par17, we applied the phage display technology. We panned 7-mer and 12-mer peptide libraries against Par17. The consensus sequence XHSXVHØ, where X can be any amino acid and Ø is a hydrophobic amino acid, was enriched from both libraries. We demonstrate the binding of this motif to the PPIase domain of Par17 using phage ELISA and NMR spectroscopy. We propose that residues Met90, Val91, Phe94, Gln95, Glu96, and Ala98 of Par17 are involved in substrate recognition, and that the phage display-selected motif XHSXVHØ can be recognized by Par17 PPIase domain in vivo.