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An excellent review of this subject was published not long ago: http://dx.doi.org/10.1107/S0907444905032130 It is even open access! But, in general the "trick" to improving diffraction is to get your molecules clean, get them to all adopt the same conformation, and then sit still. Adding a column (even if you think your prep is clean) can help, as can fractional recrystallization. Not many people know this, but even the much maligned hen egg white lysozyme doesn't diffract very well if the prep is contaminated with "lysozyme dimers", which is why commercial lysozyme is purified by fractional recrystallization. There is a heat-shock treatment described in the above paper, and of course additive screens. The reason why additive screens work seems to be because if you can get something to stick to the protein, it is more likely to sit still. -James Holton MAD Scientist On 10/18/2011 4:45 AM, Afshan Begum wrote: > > Dear ccp4 user > > I am facing one crucial problem regarding diffraction. Actually the > size of my crystal is good enough 0.5mm but it was diffracted only 4 A. > > The conditions of crystallization recipes are 4.5% PEG 1000, 0.1M Tris > and 25mM Na citrate. I really need your suggestions regarding how > can i improve my diffraction quality? > > Your support is highly appreciable. > > Best Regards > > AFSHAN > > >