Although over expression and 15N enrichment facilitate the observation of resonances from disordered proteins in Escherichia coli, 15N enrichment alone is insufficient for detecting most globular proteins. Here we explain this dichotomy and overcome the problem while extending the capability of in-cell NMR by using 19F labeled proteins. Resonances from small (~10 kDa) globular proteins containing the amino acid analog 3-fluoro-tyrosine can be observed in cells, but for larger proteins the 19F resonances are broadened beyond detection. Incorporating the amino acid analog trifluoromethyl-L-phenylalanine allows larger proteins (up to 100 kDa) to be observed in cells. We also show that site specific structural and dynamic information about both globular and disordered proteins can be obtained inside cells by using 19F NMR.

Fibrils of the intrinsically-disordered protein α-synuclein are hallmarks of Parkinson's disease. The fluorescent dye thioflavin T is often used to characterize fibrillation, but this assay may not provide quantitative information about structure and mechanism. To gain such information, we incorporated the 19F-labeled amino acid, 3-fluorotyrosine, into recombinant human α-synuclein at its endogenous tyrosine residues. Tyrosine 39 is in the positively-charged N-terminal region of this 140-residue protein. The other three, tyrosines, 125, 133, and 136, are near the C-terminus. 19F-nuclear magnetic resonance spectroscopy was used to study several properties of labeled α-synuclein, including its conformation; conformational changes induced by urea, spermine, and sodium dodecyl sulfate (SDS); its interaction with SDS micelles; and the kinetics of fibril formation. The results show that the tyrosines are in disordered regions but that there is some structure near position 39 that is disrupted by urea. SDS binding alters the conformation near position 39, but the C-terminal tyrosines are disordered under all conditions. The NMR data also indicate that SDS-micelle bound α-synuclein and the free protein exchange on the 10-ms time scale. Studies of fibrillation show the utility of 19F-labeled NMR. The data indicate that fibrillation is not accompanied by the formation of large quantities of low molecular-weight intermediates. Although dye-binding and 19F NMR data show that 1-mM SDS and 1-mM spermine accelerate aggregation compared to buffer alone, only the NMR data indicate that the species formed in SDS are smaller than those formed in buffer or buffer plus spermine. We conclude that 19F NMR spectroscopy is useful for obtaining residue-level, quantitative information about the structure, binding, and aggregation of α-synuclein.

Almost everything we know about protein biophysics comes from studies on purified proteins in dilute solution. Most proteins, however, operate inside cells where the concentration of macromolecules can be >300 mg per mL. Although reductionism-based approaches have served protein science well for over a century, biochemists now have the tools to study proteins under these more physiologically-relevant conditions. We review a part of this burgeoning post-reductionist landscape by focusing on high-resolution protein NMR spectroscopy, the only method that provides atomic-level information over an entire protein under the crowded conditions found in cells.The inside of a living cell is one of the ultimate physiologically-relevant environments, but this environment is difficult to define. The cytoplasm comprises all the material in the cell, excluding the plasma membrane and the nucleus (if present). The cytosol is the cytoplasm without organelles and other subcellular structures, such as ribosomes and the fibrous proteins that determine cell shape, motility, and material transport. It remains unclear, however, the extent to which these structures need to be considered in physiologically-relevant NMR studies. Furthermore, it is difficult to state precisely the conditions in the cytosol. The temperature for optimal growth is often considered the physiologically-relevant temperature: 37 °C for Escherichia coli and animal cells and 30 °C for yeast, although cells can survive at least for limited periods above or below these temperatures. As a general rule, the pH of the cytosol is 7.2, but it depends on extracellular conditions. The pH in E. coli cells has been monitored with NMR and covers a range from pH 6 to pH 8 (1). This range of values raises a key point: conditions inside the cell depend on the conditions outside the cell to a certain extent. Studies in E. coli show that the composition of its cytosol can be manipulated over a wide range of ionic strengths, water concentrations, and solute concentrations (2). Cells can compensate for changes in conditions, including protein over-expression, through a variety of means from simply adjusting the concentration of small hydrophilic solutes called osmolytes (3) to spatially organizing entire biosynthetic pathways (4). Finally, even the exact state of the protein under study may be difficult to define in time and space because of trafficking and posttranslational modification.

a-Synuclein function is thought to be related to its membrane binding ability. Solution NMR studies have identified several a-synuclein-membrane interaction modes in small unilamellar vesicles (SUVs), but how membrane properties affect binding remains unclear. Here, we use 19 F NMR to study a-synuclein-membrane interactions by using 3-fluoro-L-tyrosine (3FY) and trifluoromethyl-Lphenylalanine (tfmF) labeled proteins. Our results indicate that the affinity is affected by both the head group and the acyl chain of the SUV. Negatively charged head groups have higher affinity, but different head groups with the same charge also affect binding. We show that the saturation of the acyl chain has a dramatic effect on the a-synuclein-membrane interactions by studying lipids with the same head group but different chains. Taken together, the data show that a-synuclein's N-terminal region is the most important determinate of SUV binding, but its C-terminal region also modulates the interactions. Our data support the existence of multiple tight phospholipid-binding modes, a result incompatible with the model that a-synuclein lies solely on the membrane surface.

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Alkaline leaching is an important way for treating low grade metal oxide ore, which has some advantages such as low corrosion and low pollution compared to acidic leaching. In order to recover the zinc from a low grade complex zinc oxide ore in which the grade of Zn and Fe are 13 wt.% and 40.2 wt.%, respectively, and 52.8% of Zn is contained in siderite, 34.63% in limonite and 11.55% in smithsonite, this paper presents a preliminary investigation of this type of ore by alkaline leaching method. In this study, ammonia-ammonium chloride and ammonia-ammonium carbonate were used as the leaching reagents. The effects of alkaline concentration, leaching time, leaching temperature and liquid to solid ratio (L/S) were studied, respectively. The results show that 43.15% of initial Zn content was extracted adopting ammonia-ammonium chloride as the leaching reagent in 4.5M at 30°C for 3h with a liquid to solid ratio of 4:1, while 43.07% of Zn recovery was achieved employing ammonia-ammonium carbonate as the leaching reagent at 5M, 30°C and 4:1(L/S). The low leaching rate of Zn is probably attributed to that the zinc contained in siderite was not extracted completely because Zn and Fe exist as isomorphism in siderite.

In this research, a leaching study was carried out to assess the effect of several parameters on zinc extraction in a low grade complex zinc oxide ore in which the grade of Zn is 13 wt.%, and 52.8% of Zn is contained in siderite, 34.63% in limonite and 11.55% in smithsonite. The influencing parameters investigated include sulfuric acid concentration, reaction temperature, reaction time and liquid to solid ratio (L/S). The results show that over 90% of Zn can be extracted from the low grade complex zinc oxide ore when the leaching process is operated in 2M sulfuric acid at 60°C for 2.5h with a liquid to solid ratio of 6:1.

Al-pillared montmorillonite (Al-PILM) prepared with Keggin ions was studied by means of XRD, SEM-EDS and N2 adsorption-desorption isotherms.The rusults show that, compared to unpillared Na-montmorillonite (Na-M), the interlayer spacing d(001) value, BET specific surface area, surface fractal dimension and the proportion of microporous specific surface area of Al-PILM are larger and the surface is relatively rough. The BJH porous volume distribution of Al-PILM is the most probable distribution, and the most probable pore size is about 2 nm, belonging to mesopore. The porous structure of Al-PILM is characterized as parallel plate slit or “house-of-cards” wedge-shaped pore which is formed by novel meso-microporous delaminated structure and fragments. Besides, the results of elemental distribution show that the ions exchange action between Na+ and hydroxy-Al cations in pillaring solution occurs in the formation of Al-PILM.