Designed preparation for the heavy atom derivatives and its application to the structure analysis

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For the last 40 years, almost all new protein structures have been solved by the multiple isomorphous replacement (MIR) method. To apply this method for the phase problem we need to prepare good heavy-atom derivatives, which is one of the most timeconsuming process for the protein structure analysis, because it entails the trial-and-error experiments. Recently, an alternative approach has been devised for de novo phasing of protein crystals. This is the multiwavelengh anomalous diffraction (MAD) method. Especially important is the use of selenium atom for the anomalous scatterer, since it is easily incorporated into protein crystal by the protein engineering as a form of selenomethionine (Se-Met). However, there are still several difficulties in applying the method to the actual phase problems, especially at the process of deciphering the Patterson map, mainly because of the weak signal from the anomalous scatterer. In this project we applied this method to the analyzes of several new proteins for further improvement of the method and showed that this method is very useful.