26AO

E. coli peptidyl-prolyl cis-trans isomerase, mutant F4/F5Phe

Summary for 26AO

• Entry DOI: 10.2210/pdb26ao/pdb
• Descriptor: Peptidyl-prolyl cis-trans isomerase B (2 entities in total)
• Functional Keywords: peptidyl-prolyl cis-trans isomerase, non-canonical amino acids, pentafluorophenylalanine, isomerase
• Biological source: Escherichia coli K12
• Total number of polymer chains: 2
• Total formula weight: 38186.57

Authors

Frkic, R.L.,Jackson, C.J. (deposition date: 2026-04-24, release date: 2026-08-05, Last modification date: 2026-08-19)

Primary citation

Paul, N.,Welegedara, A.P.,Frkic, R.L.,Macri, L.,Thompson, T.R.C.,Baber, J.L.,Habel, E.,Abdelkader, E.H.,Qianzhu, H.,Chilton, N.F.,Jackson, C.J.,Bax, A.,Huber, T.,Otting, G.
Genetically Encoded Pentafluorophenylalanine Enables Quantitative Probing of Local Protein Malleability by 19F NMR.
J.Am.Chem.Soc., 148:32644-32655, 2026

PubMed Abstract: Aromatic ring flips in proteins provide a direct probe of local structural fluctuations, yet their rates are typically too fast for quantitative measurement by NMR spectroscopy. Here we show that site-specific incorporation of 2,3,4,5,6-pentafluoro-l-phenylalanine (F5Phe) reshapes the torsional energy landscape of aromatic side chains, slowing ring flips by over 2 orders of magnitude and shifting them into the slow-exchange regime accessible by 19F NMR. F5Phe can be genetically encoded with high fidelity and minimal structural perturbation, as confirmed by high-resolution X-ray crystallography across multiple proteins. The resulting 19F NMR spectra enable direct, quantitative measurements of ring-flip kinetics without the need for isotope labeling or complex multidimensional experiments. Application to a diverse set of proteins demonstrates that ring-flip rates vary widely even within the same hydrophobic cluster, revealing highly localized conformational fluctuations rather than global unfolding events. Pressure-dependent measurements yield small activation volumes, indicating that the structural rearrangements enabling ring flips are spatially confined. Ligand binding and protein-protein interactions modulate ring-flip rates in a site-specific manner, providing a sensitive readout of allosteric effects on local protein malleability. These results establish fluorinated aromatic amino acids as a general chemical strategy to engineer dynamic observables in proteins, transforming aromatic ring flips into a broadly applicable probe of local conformational dynamics and allostery.

PubMed: 42503665
DOI: 10.1021/jacs.6c10121

Experimental method

X-RAY DIFFRACTION (1.15 Å)