Crystals microheterogeneity

Protein contaminants can occur as natural isoforms or can arise during purification. Adventitious proteolysis and cysteine oxidation are probably the most common sources of microheterogeneity that occur during isolation (Lorber et al, 1987). This has frequently motivated the inclusion of protease inhibitors and/or reducing agents in crystallization solutions, as well as during purification. In many cases modifications that produce molecular heterogeneity are reflected in enzyme activity. For... 

Although protein microheterogeneity usually disrupts crystal formation, it can occasionally promote crystallization. For example, crystals of Escherichia coli single-stranded binding protein contain a 1 1 mixture of intact and proteolyzed protein (Ollis et ai, 1983). While crystallization experiments were initially conducted with intact protein, crystals grew only when enough molecules to form the mixed crystals had been cleaved by contaminating proteases. 

There are occasions when even the most intense efforts to crystallize a specific protein fail despite the best efforts at ultra-purification and elimination of microheterogeneity. When this occurs, an alternative is to turn to a different source of the protein. Often only very small variations in amino acid sequence, as found for example between different species of organisms, is enough to produce dramatic differences in the crystallization behavior of a protein. Thus, if the protein from one source proves intractable, consider another. With recombinant proteins, of course, one always has the option of producing a vast range of mutants. Variation of sequence in fact provides a powerful approach to crystallizing proteins when the native molecule fails. There is currently much work underway to define effective mutation strategies for protein crystallization (Derewenda, 2004 Dale et al., 2003). 

Yau, S. T., Thomas, B. R., Galkin, O., Gliko, O., and Vekilov, P. G. 2001. Molecular mechanisms of microheterogeneity-induced defect formation in ferritin crystallization. Proteins 43,343-352. 

Jiang, F.M. Kojima. S. Microheterogeneity and relaxation in 0.65Pb(Mni/3Nb2/3)03-0.35PbTi03 relaxor single crystals. Appl. Phys. Lett. 2000. 77. 1271. 

The long-range influence of the surface on crystallization, which determines the thickness of the surface layers of crystaUine pol3rmers, is comparable with the spherulite sizes (5-10)xl0 m. At a rather high amount of filler, when the distance between filler particles is lower than the spherulite size, the polymer is subjected to surface effects. In this case, the structrue and properties of pol5Tner in the surface layer must depend on the distance from the surface. In this respect, one more level of microheterogeneity of the surface layers arises, due to the influence of the surface on crystalhne structrue. 

And moreover layered stmctures attract particular interest, not only from the point of view of promising properties but also due to broad fundamental aspects of crystal chemistry and thermodynamics. Layered compoimds represent the intergrowth of blocks of different simple stmcture-types. The phase stability in such systems depends on extent of constrains between different types of stmcture and determined by equilibrium in multicomponent (different cations) microheterogeneous (different layers) system. 

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