Multiple anomalous dispersion

Carrasco, N., Buzin, Y., Tyson, E., Halpert, E., and Huang, Z. (2004). Selenium derivati-zation and crystallization of DNA and RNA oligonucleotides for X-ray crystallography using multiple anomalous dispersion. Nucleic Acids Res. 32, 1638—1646. 

Selenium modifications have been prepared as an aid to crystallography by multiple anomalous dispersion (MAD). The synthesis and incorporation into DNA of 2 -methylseleno-dC for this purpose has been described,... 

Ultimately the question of electron density map quality is answered by whether we can trace a single polypeptide or polynucleotide chain through the density in a manner consistent with the known amino acid or nucleotide sequence. In doing so, we consider the agreement between amino acid side chains and the density assigned to them, whether selenium atoms in a map experimentally determined by single (SAD) or multiple anomalous dispersion... 

Protein structures are now more often determined by using multiple anomalous dispersion (MAD) techniques. In this method, scattering that does not obey the kinematic theory is used. The kinematic theory deals with single scatter-... 

Several structurally different types of HNLs occur in nature, which likely originated hy convergent evolution from different ancestral proteins. The enzyme from almond (PaHNL) was first crystallized in 1994 and the structure was solved by multiple wavelength anomalous dispersion of a mercury derivative. The first 3D structure analysis of PaHNL was performed in 2001. ° (7 )-PaHNL from almond uses FAD as cofactor and is related to oxidoreductases it exhibits HNL activity only in the oxidized form of FAD." ... 

The anomalous components of the total scattering are wavelength dependent and the use of radiation close to an absorption edge may increase or optimise the contribution due to the anomalously scattering atoms. Ramaseshan (1962) pointed out that data collected at multiple wavelengths optimising the anomalous dispersion effects would improve the quality of phase determination. 

The X REL1 crystal structure, which consists of residues 52-316 corresponding to the N-terminal domain, was resolved using the SeMet multiple-wavelength anomalous dispersion method (9). The selenomethionines used for this method should be replaced with methionines to obtain the original form of the protein for simulations (see Note 2). 

Of course, I have just emphasized the so-called direct methods, which determine molecular structures ab initio from the observed intensities, and I have not even touched upon much larger macromolecular systems, such as proteins, which consist of thousands of atoms in the molecule. These structures also can be determined by special techniques. These include such techniques as multiple isomorphous replacement and anomalous dispersion, which take advantage of our ability to modify a given crystal containing molecules consisting of thousands of atoms by diffusing into the crystal a small number of really heavy atoms without disturbing the crystal structure. One then does the diffraction experiment on these so-called derivatives as well as on the native protein that one is interested in. 

M. Helliwell, J.R. Helliwell, V. Kaucic, N.Z. Logar, L. Barba, E. Busetto, and A. Lausi, Determination of the Site of Incorporation of Cobalt in CoZnPO-CZP by Multiple-wavelength Anomalous-dispersion Crystallography. Acta Crystallogr., Sect. B Struct. 

MWPCs have been successfully used at LURE and Stanford for multiple wavelength anomalous dispersion phasing measurements (see chapter 9). An MWPC has also been used to record Laue diffraction patterns at VEPP-3 (Gaponov et al 1989a,b,c). 

This is for multiple energy anomalous dispersion (MEAD) data collection. It is proposed that this uses a multipole wiggler of 20 periods, critical energy 9.8 keV and a calculated flux at this energy of 4.5X1014. 

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