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Integral membrane proteins (IMPs) play central roles in cellular physiology and represent the majority of known drug targets. Single-molecule fluorescence and fluorescence resonance energy transfer (FRET) methods have recently emerged as valuable tools for investigating structure–function relationships in IMPs. This review focuses on the practical foundations required for examining polytopic IMP function using single-molecule FRET (smFRET) and provides an overview of the technical and conceptual frameworks emerging from this area of investigation. In this context, we highlight the utility of smFRET methods to reveal transient conformational states critical to IMP function and the use of smFRET data to guide structural and drug mechanism-of-action investigations. We also identify frontiers where progress is likely to be paramount to advancing the field. [ABSTRACT FROM AUTHOR]

Abstract: Dc-magnetization, ac-susceptibility and x-ray diffraction (XRD) were used to investigate the microscopic origin of the magnetic property modifications induced by zinc doping in bulk and nanosized nickel ferrite, Zn x Ni1− x Fe2O4. Both the nanoparticle energy barrier to magnetization reversal, , and the bulk saturation magnetization, , are observed to initially increase with x, reach a maximum at , and eventually decrease upon further doping. XRD data do not indicate significant structural modifications at . Instead we found evidence that an indirect doping mechanism, by which Ni2+ ions are replaced by Zn2+, is responsible for the observed magnetic property enhancement. [Copyright &y& Elsevier]

Atomic force microscopy has emerged as a valuable complementary technique in membrane structural biology. The apparatus is capable of probing individual membrane proteins in fluid lipid bilayers at room temperature with spatial resolution at the molecular length scale. Protein conformational dynamics are accessible over a range of biologically relevant timescales. This chapter presents methodology our group uses to achieve robust AFM image data of the General Secretory system, the primary pathway of protein export from the cytoplasm to the periplasm of E. coli. Emphasis is given to measuring and maintaining biochemical activity and to objective AFM image processing methods. For example, the biochemical assays can be used to determine chemomechanical coupling efficiency of surface adsorbed translocases. The Hessian blob algorithm and its extension to nonlocalized linear features, the line detection algorithm, provide automated feature delineations. Many of the methods discussed here can be applied to other membrane protein systems of interest.