title: Infrequent cavity-forming fluctuations in HPr from Staphylococcus carnosus revealed by pressure- and temperature-dependent tyrosine ring flips.
abstract: Infrequent structural fluctuations of a globular protein is seldom detected and studied in detail. One tyrosine ring of HPr from Staphylococcus carnosus, an 88-residue phosphocarrier protein with no disulfide bonds, undergoes a very slow ring flip, the pressure and temperature dependence of which is studied in detail using the on-line cell high-pressure nuclear magnetic resonance technique in the pressure range from 3 MPa to 200 MPa and in the temperature range from 257 K to 313 K. The ring of Tyr6 is buried sandwiched between a beta-sheet and alpha-helices (the water-accessible area is less than 0.26 nm2), its hydroxyl proton being involved in an internal hydrogen bond. The ring flip rates 10(1)-10(5) s(-1) were determined from the line shape analysis of H(delta1, delta2) and H(epsilon1,epsilon2) of Tyr6, giving an activation volume DeltaV++ of 0.044 +/- 0.008 nm3 (27 mL mol(-1)), an activation enthalpy DeltaH++ of 89 +/- 10 kJ mol(-1), and an activation entropy DeltaS++ of 16 +/- 2 JK(-1) mol(-1). The DeltaV++) and DeltaH++ values for HPr found previously for Tyr and Phe ring flips of BPTI and cytochrome c fall within the range of DeltaV(double dagger) of 28 to 51 mL mol(-1) and DeltaH++ of 71 to 155 kJ mol(-1). The fairly common DeltaV++ and DeltaH++ values are considered to represent the extra space or cavity required for the ring flip and the extra energy required to create a cavity, respectively, in the core part of a globular protein. Nearly complete cold denaturation was found to take place at 200 MPa and 257 K independently from the ring reorientation process.
authors.affiliation: Department of Molecular Science, Graduate School of Science and Technology, Kobe University, Japan.
authors.forename: Mineyuki
authors.initials: M
authors.lastname: Hattori
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Yamada
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Akasaka
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hengstenberg
authors.forename: Wolfram
authors.initials: W
authors.lastname: Gronwald
authors.forename: Hans Robert
authors.initials: HR
authors.lastname: Kalbitzer
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000737:chemistry*; D011312:Pressure; D011489:Protein Denaturation; D013210:Staphylococcus / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D014443:Tyrosine; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C030182:phosphocarrier protein HPr