title: Cyclophilin A catalyzes proline isomerization by an electrostatic handle mechanism.
abstract: Proline isomerization is a ubiquitous process that plays a key role in the folding of proteins and in the regulation of their functions. Different families of enzymes, known as "peptidyl-prolyl isomerases" (PPIases), catalyze this reaction, which involves the interconversion between the cis and trans isomers of the N-terminal amide bond of the amino acid proline. However, complete descriptions of the mechanisms by which these enzymes function have remained elusive. We show here that cyclophilin A, one of the most common PPIases, provides a catalytic environment that acts on the substrate through an electrostatic handle mechanism. In this mechanism, the electrostatic field in the catalytic site turns the electric dipole associated with the carbonyl group of the amino acid preceding the proline in the substrate, thus causing the rotation of the peptide bond between the two residues. We identified this mechanism using a combination of NMR measurements, molecular dynamics simulations, and density functional theory calculations to simultaneously determine the cis-bound and trans-bound conformations of cyclophilin A and its substrate as the enzymatic reaction takes place. We anticipate that this approach will be helpful in elucidating whether the electrostatic handle mechanism that we describe here is common to other PPIases and, more generally, in characterizing other enzymatic processes.
authors: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom;
authors: Carlo
authors: C
authors: Camilloni
authors: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom;
authors: Aleksandr B
authors: AB
authors: Sahakyan
authors: Department of Biochemistry and Molecular Genetics, University of Colorado, Aurora, CO 80045;
authors: Michael J
authors: MJ
authors: Holliday
authors: William R. Wiley Environmental Molecular Sciences Laboratory, High Field NMR Facility, Richland, WA 99532; and.
authors: Nancy G
authors: NG
authors: Isern
authors: National High Magnetic Field Laboratory, Tallahassee, FL 32310.
authors: Fengli
authors: F
authors: Zhang
authors: Department of Biochemistry and Molecular Genetics, University of Colorado, Aurora, CO 80045;
authors: Elan Z
authors: EZ
authors: Eisenmesser
authors: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; mv245@cam.ac.uk.
authors: Michele
authors: M
authors: Vendruscolo
mesh_terms: D002384:Catalysis; D021984:Cyclophilin A / Q000737:chemistry*; D006801:Humans; D056004:Molecular Dynamics Simulation; D019906:Nuclear Magnetic Resonance, Biomolecular; D011392:Proline / Q000737:chemistry*; D055672:Static Electricity
chemical_list: D011392:Proline; D021984:Cyclophilin A
keywords: NMR spectroscopy; enzyme catalysis