Hello everyone, I would like to share my experience with one dataset and request some advice on which is the best way to prove a conformational change seen in a density map.
The first issue arose when we were looking for an extra ribosomal factor added to a crystalized ribosome. After careful data collection and refinement (I/sigma last shell 1.2, 3.1A and CC1/2 around 22%) the sigma-A-weighted maps 2mFo-DFc and Fo-Fc does not show any clear difference density that we could interpret as the expected factor. Interestingly, a computed map with coefficients 3mFo-2DFc started to show some features that clearly could be explained as a fragment of the factor. The density improved even more with a B-sharpened map. We have seen this behavior before and I was wondering if someone else is using this kind of maps and may could explain the reason behind this density improvement. Is it a crazy idea to go even higher like 4mFo-3DFc? The second query has to do with which is the best way to prove that a conformational change is present in an specific residue (in this case and RNA base) in your structure. To my knowledge, a classic omit map with simulated annealing would do the job regarding removing the model bias. Actually, I found an interesting alternative in PHENIX called a Kick map, were a series of maps computed from a ramdoinised set of models yields a averaged map ideally free from model bias. Does anyone has a preference for any of those schemes? Are there more alternative to prove a conformational change in a model phased with a molecular replacement solution? Thank you very much in advance. -- Israel Sanchez Fernandez PhD Ramakrishnan-lab MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 0QH, UK
