Dear All,
We have an anisotropic dataset of 3.3 A and it was solved (not by me) with P6522 with R/freeR
29.1/37.3.
I got the corrected
mtz file by plugging in the .HKL (P6122) file to anisotropy diffraction server at
2.04 A. I reindexed this p6122 to p6522 and extended the resolution and refined
(refmac) the structure to R/freeR
36.40/38.50. With aotoncs option, fixing all Ramachnadran and rotamer
outliers I got it 30/32. When I added waters and it went down to 27.5/31.2. At
this point I recognized that my new .mtz file from anisotropy server has
different R flag than the earlier one (3.3A) so I copied the R flag and did refinemnt to get R/Rfree 0.2682/0.3247. When I looked at
the refined structure I found more outliers
than I fixed in earlier round. I did fix all the outliers and without NCS and
waters it gives R/Rfree 0.2906/0.3325. At all the stages I look at outliers at
molprobity server which suggested structure is 10th percentile and after
refinement more outliers comes back. At stage-1 map looked far better so was
happy that anisotropy correction has worked for me (this was my first time
handling this type of dataset) but further refinement didn’t make it look any
better.I use both refmac and autoBuster for refinement.
This protein is an human enzyme and a bacterial homologue which has 38% identity has been used to solve the Apo structure (2.7 A, pC2221, R/freeR 23.03/27.96, molprobity is around 50th percentile). I looked in to this I try to fix all the outliers and try to improve molprobity score but it just refused to improve as after refinement I get more outliers. This Apo structure was used to solve the mutant structure at 3.3 A. I believe that both structure could have better R/freeR and excellent molprobity scores than what they have now. I am not able to recognise if there is any problem in Apo structure and if errors have come to mutant so both of them refuse to improve.
I wondered if there is any model bias (I don’t know if it’s
the case but nothing was coming to my mind) so thought using ARP/wARP classic
to build model from existing model but it complained that "The wilson plot
is very bad and ARp/wARP is very unlikely to run in a sensible way. Please
check your data" .
At this point I dont know how to systematically dissect this problem. I know there could be wrong in several places but with my only '2-3 structure experience' I am not able to identify the regions to look for
error but I think something is not right. I really appreciate if you give me
some suggestions/ideas/directions/tips so that I could recognize problem and
improve structure and learn some more.
I appreciate your valuable time.
Regards,
Rajesh