EDM-DEDM and protein crystal structure solution.
Electron-density modification (EDM) procedures are the classical tool for driving model phases closer to those of the target structure. They are often combined with automated model-building programs to provide a correct protein model. The task is not always performed, mostly because of the large initial phase error. A recently proposed procedure combined EDM with DEDM (difference electron-density modification); the method was applied to the refinement of phases obtained by molecular replacement, ab initio or SAD phasing [Caliandro, Carrozzini, Cascarano, Giacovazzo, Mazzone & Siliqi (2009), Acta Cryst. D65, 249-256] and was more effective in improving phases than EDM alone. In this paper, a novel fully automated protocol for protein structure refinement based on the iterative application of automated model-building programs combined with the additional power derived from the EDM-DEDM algorithm is presented. The cyclic procedure was successfully tested on challenging cases for which all other approaches had failed.
Caliandro
Rocco
R
Institute of Crystallography, Consiglio Nazionale della Ricerche, Via G. Amendola 122/0, Bari, Italy.
Carrozzini
Benedetta
B
Cascarano
Giovanni Luca
GL
Giacovazzo
Carmelo
C
Mazzone
Anna Maria
AM
Siliqi
Dritan
D
D000465:Algorithms; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods* / Q000706:statistics & numerical data; D004583:Electrons; D008956:Models, Chemical; D008958:Models, Molecular; D011336:Probability; D011487:Protein Conformation; D012984:Software