Three-dimensional protein-based techniques

Aside from the direct techniques of X-ray or electron diffraction, the major possible routes to knowledge of three-dimensional protein structure are prediction from the amino acid sequence and analysis of spectroscopic measurements such as circular dichroism, laser Raman spectroscopy, and nuclear magnetic resonance. With the large data base now available of known three-dimensional protein structures, all of these approaches are making considerable progress, and it seems possible that within a few years some combination of noncrystallo-graphic techniques may be capable of correctly determining new protein structures. Because the problem is inherently quite difficult, it will undoubtedly be essential to make the best possible use of all hints available from the known structures. 

The following analysis and discussion of protein structure is based almost exclusively on the results of three-dimensional X-ray crystallography of globular proteins. In addition, one structure is included that was determined by electron diffraction (purple membrane protein), and occasional reference is made to particularly relevant results from other experimental techniques or from theoretical calculations. Even with this deliberately restricted viewpoint the total amount of information involved is immense. Millions of independent parameters have been determined by protein crystallography, and the relationships among almost any subset of them are of potential interest. A major aim of the present study is to provide a guide map for use in exploring this forest of information. 

Most proteins must be folded into a specific three-dimensional conformation to express their specificity and activities, which comphcates the DSP [212]. Researchers in the area of RME of proteins/enzymes have reafized this and directed more efforts in developing novel and imaginative techniques in RME as well as coupling the existing techniques such as chromatography, electrophoresis, and membrane extractions with RME. Such promising techniques developed in the recent past have been discussed in this section. Apart from these techniques, use of novel surfactants in the RME and surfactant based separation processes (e.g., cloud-point extraction) are also considered. 

The chemical and physical behaviour of proteins is very complex and the prediction of these characteristics has met with limited success as studies on these materials are based upon empirical measurements. The difficulties lie in the lack of understanding of protein structures only a few three dimensional structures are known in detail, and the systems in which have been studied are very simple. Studies of complex systems of mixtures or of inter-molecular interactions are limited and the appropriate techniques have yet to be developed. However, with advances in the molecular modelling of proteins, it is becoming possible to predict more of their physical and chemical behaviour and modelling is now a major area of research activity.08 ... 

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