Does the self-rotation function suggest presence of NCS axes? If so, this may help you figure out the symmetry inside the a.u..

If you haven't done so already, try diffracting a crystal at room temperature, to make sure cryo-protection and freezing did not affect the diffraction.

In any case, at 3.65Å I would recommend not to spend too much of your time on this dataset. 

Just set your computer(s) to try MR with different parameters, numbers of copies to search for etc. Instead of 40 copies at 50% solvent, you may have down to 20 copies with 75% solvent (or maybe even less). Or more than 40 with less solvent (perhaps less likely). Even then, judging whether an MR solution is really correct might still not be that easy.

And in the meantime spend your own time to try to get derivatives and better-diffracting crystals. At better than 2.5Å resolution it will all be much easier, for instance auto-building with your input sequence will allow much better identification of correct MR solutions. 

And if you are lucky, a heavy atom soaking experiment might actually improve the crystal. 

If you haven't already, I'd also try to get some complementary information on whether your protein forms stable complexes. EM, SAXS and AUC come to mind.

Good luck!

Mark J van Raaij
Dpto de Estructura de Macromoleculas
Centro Nacional de Biotecnologia - CSIC
calle Darwin 3
E-28049 Madrid, Spain
tel. (+34) 91 585 4616
http://wwwuser.cnb.csic.es/~mjvanraaij

On 26 Apr 2017, at 21:34, Jademilson Santos <[log in to unmask]> wrote:

Greetings all,

I am having trouble with a data set and would like to know if somebody can help. I'm working with a protein of approximately 50 kDa, which I have successfully crystallized. The crystals diffracted at a resolution of 3,65 angstroms and upon initial processing using XDS i obtained the following information:

space group: P21

ISA = 33.3

cell unit: a=285.2, b=135.9, c= 287.5, α=90, β=117.5, γ=90

Matthews coefficient indicates that there are 40 molecules in the asymmetric unit

I am currently running the program Phaser (Phenix) to determine the phase via molecular replacement with a model that has 49% homology and query coverage of 94% and the program is taking extremly long to finish. In this case in which there is an extremly high number of molecules in the asymmetric unit, is this actually possible? Does someone know how to work with these values and is there a specific strategy which i must follow?

Regards

Jademilson Celestino dos Santos

Laboratory of Applied Structural Biology

Department of Microbiology
Institute of Biomedical Sciences
University of São Paulo- USP