The ab initio crystal structure solution of proteins by direct methods. II. The procedure and its first applications.

A direct phasing method is described that is potentially able to solve ab initio protein structures. The method uses the information contained in diffraction data of the native structure and of one isomorphous derivative. The various steps of the procedure are analysed in order to estimate their robustness against experimental errors in measurements and lack of isomorphism. Experimental tests involve four typical protein structures and show that crystal structure solution is attained in a rather straightforward way.