Protein Conformational Changes in the Bacteriorhodopsin Photocycle: Comparison of Findings from Electron and X-Ray Crystallographic Analyses

Light-driven conformational changes in the membrane protein bacteriorhodopsin have been studied extensively using X-ray and electron crystallography, resulting in the deposition of >30 sets of coordinates describing structural changes at various stages of proton transport. Using projection difference Fourier maps, we show that coordinates reported by different groups for the same photocycle intermediates vary considerably in the extent and nature of conformational changes. The different structures reported for the same intermediate cannot be reconciled in terms of differing extents of change on a single conformational trajectory. New measurements of image phases obtained by cryo-electron microscopy of the D96G/F171C/F219L triple mutant provide independent validation for the description of the large protein conformational change derived at 3.2 Å resolution by electron crystallography of 2D crystals, but do not support atomic models for light-driven conformational changes derived using X-ray crystallography of 3D crystals. Our findings suggest that independent determination of phase information from 2D crystals can be an important tool for testing the accuracy of atomic models for membrane protein conformational changes

Transport of cryptates as model brownons: electrical mobilities and self-diffusion coefficients of monovalent and divalent ions cryptated by 222 in aqueous solutions

Cryptates present a quasi-spherical symmetry and a practically const. size for a charge varying from 0 (unchanged empty cryptand) to 1 or 2 (cryptand contg. a monovalent or divalent cation). They are therefore sensible models of heavy and large particles undergoing Brownian motion (brownons). Their transport properties in aq. solns., electrophoretic mobilities, and self-diffusion coeffs. are in good agreement with this Brownian dynamical model

Lithium bromide in acetonitrile: thermodynamics, theory, and simulation

A variety of methods was used for the study of lithium bromide solns. in acetonitrile yielding by their combination reliable information on different levels of approxn. Osmotic coeffs. based on precise vapor pressure measurements are reproduced by CM (chem. model) and HNC (hypernetted chain) calcns. and by BD (brownian dynamics) simulations. The results of neutron scattering expts. are treated with the help of HNC and BD methods. Hartree-Fock calcns. on isolated LiBr pairs and solvated lithium ions yield reliable distances and reveal the geometry of the lithium solvation sphere