Hi Rhys, there is nothing wrong with experimental phases. If a few MR attempts fail, there aren't any real red flags with your crystal form, and you have a few decently diffracting crystals at hand, soak them for a little bit in your favourite heavy atom. We found that soaks in 500-1000mM Na or K iodide in your precipitant solution are very successful. Many crystals tolerate such high iodide concentrations well. Iodide has a very strong anomalous signal in house and binds to a variety of sites. For SSGCID, this has become our main technique to obtain experimental phases. With the great software packages available nowadays, you can have an initial structure within minutes after finishing the data set.
For a recent review of this old technique see here: http://www.ncbi.nlm.nih.gov/pubmed/21359836 Best wishes, Jan -- Jan Abendroth Emerald BioStructures / SSGCID Seattle / Bainbridge Island WA, USA home: Jan.Abendroth_at_gmail.com work: JAbendroth_at_embios.com http://www.emeraldbiostructures.com On Oct 1, 2012, at 12:26 PM, RHYS GRINTER <r.grinte...@research.gla.ac.uk> wrote: > Hi All, > > I'm currently working on solving the structure of a protein by molecular > replacement. The protein is around 30kDa and likely has a two beta-prism > domains, linked by a long curved two stranded sheet based on the structure of > an analogue. There are also a number of other structures which represent a > single homologous beta-prism domain. > I've tried to find MR solution using the analogue and various truncation/AA > substitution models based on it with no success. I've also tried single > domain ensembles of the other homologous structures, also with no success. I > think the problem is the overall sequence homology is quite low between my > protein and the available structures (35% for the analogue and around 20% for > the other models. > > I was curious as to how someone with more experience would tackle this > problem. > > Just for background, the datasets I have are 2 to 2.7 angstroms with pretty > nice stats. The space group is most likely C2221 with two molecules per ASU > (giving around 58% solvent). > > Thanks, > > Rhys Grinter > PhD Candidate > University of Glasgow
