Diffraction multiwavelength anomalous

Phase information can also be obtained by Multiwavelength Anomalous Diffraction experiments... 

The intensity differences obtained in the diffraction pattern by illuminating such a crystal by x-rays of different wavelengths can be used in a way similar to the method of multiple isomorphous replacement to obtain the phases of the diffracted beams. This method of phase determination which is called Multiwavelength Anomalous Diffraction, MAD, and which was pioneered by Wayne Hendrickson at Columbia University, US, is now increasingly used by protein cystallographers. 

X-ray data are recorded either on image plates or by electronic detectors The rules for diffraction are given by Bragg s law Phase determination is the major crystallographic problem Phase information can also be obtained by Multiwavelength Anomalous Diffraction experiments... 

Hendrickson WA, Horton JR, LeMaster DM. Selenomethionyl proteins produced for analysis by multiwavelength anomalous diffraction (MAD) a vehicle for direct determination of three-dimensional structure. EMBO J... 

Membrane-integrated proteins were always hard to express in cell-based systems in sufficient quantity for structural analysis. In cell-free systems, they can be produced on a milligrams per milliliter scale, which, combined with labeling with stable isotopes, is also very amenable forNMR spectroscopy [157-161]. Possible applications of in vitro expression systems also include incorporation of selenomethionine (Se-Met) into proteins for multiwavelength anomalous diffraction phasing of protein crystal structures [162], Se-Met-containing proteins are usually toxic for cellular systems [163]. Consequently, rational design of more efficient biocatalysts is facilitated by quick access to structural information about the enzyme. 

Multiwavelength anomalous diffraction Makes use of atoms within a protein that diffract X-rays anomalously. Commonly uses seleno-methionine residues in place of methionines. 

Hendrickson, W. A., et al. (1986). Structure of D-selenolanthionine determined directly from multiwavelength anomalous diffraction of bremstrahlung. Am. Crystallogr Assoc Series 2 (Abstract) 14,48. 

La Fortelle, E. D. and Bricogne, G. (1997). Maximum-likelihood heavy-atom parameter refinement for multiple isomorphous replacement and multiwavelength anomalous diffraction methods. Method Enzymol. 276, 472 94. 

Ramakrishnan, V. and Biou, V. (1997). Treatment of multiwavelength anomalous diffraction data as a special case of multiple isomorphous replacement. Method Enzymol. 276, 538-557. 

Smith, J. L. (1991). Determination of three-dimensional structure by multiwavelength anomalous diffraction. Current Opin. Struct. Biol 1,1002-1011. 

The tem ARO/CYC crystal structure was solved to 1.9 A using the multiwavelength anomalous diffraction (MAD) method. Our model reveals the following conclusions ... 

Kinetic analysis gave Km values of 67 pM for formaldehyde and 56 pM for NAD+, and suggested that the reaction proceeds by a ping-pong mechanism. The enzyme catalyzed the oxidation of formaldehyde accompanied by the stoichiometric reduction of NAD", but no reverse reaction was observed. The crystal structure of FaidDH from Pseudomonas putida (PFDH) has been solved by the multiwavelength anomalous diffraction method using intrinsic zinc ions and has been refined at a 1.65 A resolution (Fig. 9.3) [87]. 

---