Protein complexes native

Wittig, I., Karas, M., and Schagger, H. (2007) High resolution clear native electrophoresis for in-gel functional assays and fluorescence studies of membrane protein complexes. Mol. Cell. Proteomics 6, 1215-1225. 

Once a suitable crystal is obtained and the X-ray diffraction data are collected, the calculation of the electron density map from the data has to overcome a hurdle inherent to X-ray analysis. The X-rays scattered by the electrons in the protein crystal are defined by their amplitudes and phases, but only the amplitude can be calculated from the intensity of the diffraction spot. Different methods have been developed in order to obtain the phase information. Two approaches, commonly applied in protein crystallography, should be mentioned here. In case the structure of a homologous protein or of a major component in a protein complex is already known, the phases can be obtained by molecular replacement. The other possibility requires further experimentation, since crystals and diffraction data of heavy atom derivatives of the native crystals are also needed. Heavy atoms may be introduced by covalent attachment to cystein residues of the protein prior to crystallization, by soaking of heavy metal salts into the crystal, or by incorporation of heavy atoms in amino acids (e.g., Se-methionine) prior to bacterial synthesis of the recombinant protein. Determination of the phases corresponding to the strongly scattering heavy atoms allows successive determination of all phases. This method is called isomorphous replacement. 

Size-based analysis of SDS-protein complexes in polyacrylamide gels (SDS-PAGE) is the most common type of slab gel electrophoresis for the characterization of polypeptides, and SDS-PAGE is one of the most commonly used methods for the determination of protein molecular masses.117 The uses for size-based techniques include purity determination, molecular size estimation, and identification of posttranslational modifications.118119 Some native protein studies also benefit from size-based separation, e.g., detection of physically interacting oligomers. 

The CD features of bacteriochlorophyll a in light-harvesting bacteriochlorophy 11-protein complexes from native bacteria is more interesting and is not compatible with Boxer s experiments. Bacteriochlorophyll(Bchl)-protein complexes exhibit various CD spectral profiles, depending on the species of bacteria and their culture conditions 201 206). Thus, CD of Bchl arises from the asymmetric environment in which the Bchl is situated, and from the specialized arrangement which affords a specific interaction between Bchl molecules, as well as from the asymmetry of Bchl... 

It is necessary to forewarm milk to impart adequate heat stability to the concentrate to permit it to withstand subsequent sterilization treatments. The heat-induced casein micelle-whey protein complexes in forewarmed milk are less sensitive to heat than native whey proteins and thus provide the required stability to the concentrate. The forewarming treatment also stabilizes the milk mineral system by com-plexing Ca and Mg ions with casein micelles and by converting ionic forms to the less reactive form of colloidal phosphate (Morr 1975). 

Farr CD, Gafken PR, Noibeck AD, et al. Proteomic analysis of native metabotropic glutamate receptor 5 protein complexes reveals novel molecular constituents. J Neurochem 2004 91 438-450. 

Recently, the crystal structure of S-protein complexed with the model peptide has been solved to moderate resolution (3 A) (Taylor et al., 1985). Most of the structural features envisioned in the design of the model peptide were indeed observed in the structure of the complex. The peptide is in a helical conformation, the histidine is held in a reasonable orientation for catalysis, and the complex is stabilized by nonbonded interactions between the hydrophobic cleft of S-protein and the side chains of Phe-8 and Met-13 of the peptide. There were also a number of subtle differences between the structures of the native and the model S-protein S-peptide complexes. Most notably, the N terminus of the peptide has undergone a major reorientation that prevents Glu-2 from forming a hydrogen bond with Arg-10. Further, the 8-nitrogen of the active-site... 

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