Solution structure of Escherichia coli Par10: The prototypic member of the Parvulin family of peptidyl-prolyl cis/trans isomerases

E. coli Par 10 is a peptidyl-prolyl cis/trans isomerase (PPIase) from Escherichia coli catalyzing the isomerization of Xaa-Pro bonds in oligopeptides with a broad substrate specificity. The structure of E. coli ParlO has been determined by multidimensional solution-state NMR spectroscopy based on 1207 conformational constraints (1067 NOE-derived distances, 42 vicinal coupling-constant restraints, 30 hydrogen-bond restraints, and 68 Φ/Ψ restraints derived from the Chemical Shift Index). Simulated-annealing calculations with the program ARIA and subsequent refinement with XPLOR yielded a set of 18 convergent structures with an average backbone RMSD from mean atomic coordinates of 0.50 ̊ within the well-defined secondary structure elements. E. coli Par1 0 is the smallest known PPIase so far, with a high catalytic efficiency comparable to that of FKBPs and cyclophilins. The secondary structure of E. coli Par10 consists of four helical regions and a four-stranded antiparallel β-sheet. The N terminus forms a β-strand, followed by a large stretch comprising three α-helices. A loop region containing a short β-strand separates these helices from a fourth α-helix. The C terminus consists of two more β-strands completing the four-stranded anti-parallel β-sheet with strand order 2143. Interestingly, the third β-strand includes a Gly-Pro cis peptide bond. The curved β-strand forms a hydrophobic binding pocket together with α-helix 4, which also contains a number of highly conserved residues. The three-dimensional structure of Par10 closely resembles that of the human proteins hPin1 and hPin14 and the plant protein Pin1At, belonging to the same family of highly homologous proteins.