160 research outputs found
Author Correction: Temperature dependence of protein-water interactions in a gated yeast aquaporin
No full textA correction to this article has been published and is linked from the HTML version of this paper. The error has been fixed in the paper.</jats:p
Temperature dependence of protein-water interactions in a gated yeast aquaporin
No full textAbstractRegulation of aquaporins is a key process of living organisms to counteract sudden osmotic changes. Aqy1, which is a water transporting aquaporin of the yeast Pichia pastoris, is suggested to be gated by chemo-mechanical stimuli as a protective regulatory-response against rapid freezing. Here, we tested the influence of temperature by determining the X-ray structure of Aqy1 at room temperature (RT) at 1.3 Å resolution, and by exploring the structural dynamics of Aqy1 during freezing through molecular dynamics simulations. At ambient temperature and in a lipid bilayer, Aqy1 adopts a closed conformation that is globally better described by the RT than by the low-temperature (LT) crystal structure. Locally, for the blocking-residue Tyr31 and the water molecules inside the pore, both LT and RT data sets are consistent with the positions observed in the simulations at room-temperature. Moreover, as the temperature was lowered, Tyr31 adopted a conformation that more effectively blocked the channel, and its motion was accompanied by a temperature-driven rearrangement of the water molecules inside the channel. We therefore speculate that temperature drives Aqy1 from a loosely- to a tightly-blocked state. This analysis provides high-resolution structural evidence of the influence of temperature on membrane-transport channels.</jats:p
Faculty Opinions recommendation of Macromolecular diffractive imaging using imperfect crystals.
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Acceleration and optical interferometry
No full textThe influence of acceleration on a number of physical systems is examined. We present a full relativistic treatment of a simple harmonic oscillator with relativistic velocities. The line element for Schwarzschild geometry is expanded in a set of Cartesian coordinates and is shown to be locally equivalent (neglecting curvature) to the line element of a linearly accelerating frame of reference. We consider the rate of a linearly accelerating quantum mechanical clock and the measurement of frequency by non-inertial observers, requiring this measurement to be of finite duration. These analyses demonstrate the standard measurement hypothesis for accelerating observers only approximates the physical behaviour of these systems.
We derive the output of an optical ring interferometer in a variety of experimental contexts. A full relativistic reanalysis of the modified Laub drag experiment of Sanders and Ezekiel is performed, correcting a number of errors in their work and giving an overall discrepancy between experiment and theory of 1300 ppm. We examine the behaviour of a ring interferometer containing an accelerating glass sample. Our analysis predicts sideband structure will arise when a glass sample is oscillated along one arm of a Mach-Zehnder interferometer and the resulting output Fourier analysed. We also predict a resonant cavity containing a linearly accelerating glass sample will display optical ringing. A rigorous analysis of a ring interferometer with angular acceleration is presented. This predicts a resonant cavity with angular acceleration will also display optical ringing and demonstrates the beat frequency in a ring laser with angular acceleration is the instantaneous Sagnac beat frequency. Finally, we analyse the optical output of a rotating ring laser with one mirror oscillating, predicting sideband structure in spectra obtained from Fourier analysis of the beat between the opposite beams, and the beat between adjacent modes when the laser has multimode operation
Opportunities and challenges for time-resolved studies of protein structural dynamics at X-ray free-electron lasers
No full textX-ray free-electron lasers (XFELs) are revolutionary X-ray sources. Their time structure, providing X-ray pulses of a few tens of femtoseconds in duration; and their extreme peak brilliance, delivering approximately 10(12) X-ray photons per pulse and facilitating sub-micrometre focusing, distinguish XFEL sources from synchrotron radiation. In this opinion piece, I argue that these properties of XFEL radiation will facilitate new discoveries in life science. I reason that time-resolved serial femtosecond crystallography and time-resolved wide angle X-ray scattering are promising areas of scientific investigation that will be advanced by XFEL capabilities, allowing new scientific questions to be addressed that are not accessible using established methods at storage ring facilities. These questions include visualizing ultrafast protein structural dynamics on the femtosecond to picosecond time-scale, as well as time-resolved diffraction studies of non-cyclic reactions. I argue that these emerging opportunities will stimulate a renaissance of interest in time-resolved structural biochemistry
Crystal structure of a yeast aquaporin at 1.15 angstrom reveals a novel gating mechanism.
No full textAquaporins are transmembrane proteins that facilitate the flow of water through cellular membranes. An unusual characteristic of yeast aquaporins is that they frequently contain an extended N terminus of unknown function. Here we present the X-ray structure of the yeast aquaporin Aqy1 from Pichia pastoris at 1.15 A resolution. Our crystal structure reveals that the water channel is closed by the N terminus, which arranges as a tightly wound helical bundle, with Tyr31 forming H-bond interactions to a water molecule within the pore and thereby occluding the channel entrance. Nevertheless, functional assays show that Aqy1 has appreciable water transport activity that aids survival during rapid freezing of P. pastoris. These findings establish that Aqy1 is a gated water channel. Mutational studies in combination with molecular dynamics simulations imply that gating may be regulated by a combination of phosphorylation and mechanosensitivity
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