Structure X-Ray Crystallography

X-Ray Crystallography. Structural data exists on more than one thousand steroids. Comparisons of the conformations obtained by x-ray crystallography have been made to the conformations obtained by other methods (161). Several studies use x-ray crystal stmctures in the study of progestins. 

Crane BR, Siegel LM, Getzoff ED. Probing the catalytic mechanism of sulfite reductase by X-ray crystallography Structures of the Escherichia coli hemoprotein in complex with substrates, inhibitors, intermediates, and products. Biochemistry 1997 36 12120-37. 

Low solubility or improper folding may sometimes hamper the use of enzymes, particularly when expressed in a non-native host. A method of expressing proteins with a C -terminal GFP fusion to use fluorescence as a measure of the amount of correctly folded protein has been introduced (44). DNA shuffling produced variants of ferritin that showed increased solubility, even when they were recloned without the GFP fusion. This assay has been used to produce proteins for X-ray crystallography structure determination (45). The protein nucleoside diphosphate kinase from Pyrobaculum aerophilum is insoluble when expressed in E. coli, but after DNA shuffling, a functional variant with six mutations was found to have 90% solubility, which enabled its crystallization, and its structure was determined. 

An X-ray crystallography structure of the duplex from d(ATA UAT) and d( ATAT AT) demonstrates that an alternative to the classical B-DNA double helix is possible. This sequence is found not only in TATA boxes, but also in other regulatory regions of DNA. The structure is not related to those found in triplexes or to parallel DNA duplexes, though its conformational parameters are very similar to those of B-form DNA. Bases of the two antiparallel strands form Hoogsteen pairs, with adenines in the syn conformation. 

Figure 7.3 ACHE X-ray crystallography structures (pdb lamn). (a) Ribbon display structure depiction with X-ray crystallographic water molecules illustrated and bound substrate depicted in the CPK display mode. Colour coding is as follows Hydrogen White Oxygen Red Nitrogen Blue Carbon Grey. In this structure, sulphate (Sulphur Yellow) is also included, (b) Close-up of active site to show dense hydrogenbonding network (bright yellow). Bound substrates and water molecules are shown in the stick display mode. The protein polypeptide is also shown in CA display mode.

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