New developments in 'pure' direct methods for protein crystallography

'pure' direct method is an ab initio method. Recent advances in ab initio d irect methods have enabled the solution of crystal structure of small prote in from the type and number of atoms in cell as well as native X - ray date that must be available to atomic resolution, that is, without the use of f ragments of known structure or the need to prepare heavy - atom derivatives . An approach that is gaining rapidly in popularity is dual space recycling methods SnB and SHELX - D. They have recently solved the previously known structure of triclinic lysozyme consisting of 1001 non - H protein atoms, n one heavier than sulfur. The system optimization method has developed from the integration of systematization, optimization and the probability distri bution of structure - invariant. Its program is called SYSTEM - 99.On it th ere is one effective objective function, which is out of ordinary, accordin g to size of the structure, intensity and extensity of relations between re flections, it divides reflections into many subsystems. Then by means of mi nimization in objective function, it determines all die phases among subsys tem in reciprocal space. The SYSTEM - 99 program was able to solve the stru cture of trichosanthes root(TCS) that contains with 1914 non - H protein at oms none heavier than sulfur.