title: Wide-dynamic-range kinetic investigations of deep proton tunnelling in proteins.
abstract: Directional proton transport along 'wires' that feed biochemical reactions in proteins is poorly understood. Amino-acid residues with high pKa are seldom considered as active transport elements in such wires because of their large classical barrier for proton dissociation. Here, we use the light-triggered proton wire of the green fluorescent protein to study its ground-electronic-state proton-transport kinetics, revealing a large temperature-dependent kinetic isotope effect. We show that 'deep' proton tunnelling between hydrogen-bonded oxygen atoms with a typical donor-acceptor distance of 2.7-2.8 Å fully accounts for the rates at all temperatures, including the unexpectedly large value (2.5 × 10(9) s(-1)) found at room temperature. The rate-limiting step in green fluorescent protein is assigned to tunnelling of the ionization-resistant serine hydroxyl proton. This suggests how high-pKa residues within a proton wire can act as a 'tunnel diode' to kinetically trap protons and control the direction of proton flow.
authors.affiliation: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Bridget
authors.initials: B
authors.lastname: Salna
authors.affiliation: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Abdelkrim
authors.initials: A
authors.lastname: Benabbas
authors.affiliation: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: J Timothy
authors.initials: JT
authors.lastname: Sage
authors.affiliation: Division of Molecular Biosciences, South Kensington campus, Imperial College London, SW7 2AZ London, UK.
authors.forename: Jasper
authors.initials: J
authors.lastname: van Thor
authors.affiliation: Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Paul M
authors.identifier: 0000-0001-6958-2836
authors.initials: PM
authors.lastname: Champion
mesh_terms: D049452:Green Fluorescent Proteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D007700:Kinetics; D008956:Models, Chemical; D011487:Protein Conformation; D011522:Protons; D013696:Temperature
chemical_list: D011522:Protons; D049452:Green Fluorescent Proteins