Lisa, As others have said, using careful data collection and the modern program suites available (SHARP, Phenix, etc.), a 300 KD complex with 111 Se-Met residues should be quite solvable. But you didn't state is what is in the asymmetric unit (the important figure): one complex with 111 Se-Met residues or 111 Se-Met residues and > 300KD in the ASU.
We recently solved a structure by SAD with >750 KD of protein and 114 Se-Met residues in the ASU. The anomalous signal at 3.1 A was strong enough to find 109 Se-Met residues and trace about 70% of the chain after the first round of phasing. While we had the potential of NCS to work with, conformational changes between the different monomers meant that NCS methods could not be used in the initial phasing. Trying also James' suggestion of differential labeling and/or including MIRAS methods (Hg, Pt, Sm, etc.) with Se-Met protein should increase your chances. With modern beamlines, you can tune to the most optimal wavelengths for data collection. Good hunting, Michael **************************************************************** R. Michael Garavito, Ph.D. Professor of Biochemistry & Molecular Biology 603 Wilson Rd., Rm. 513 Michigan State University East Lansing, MI 48824-1319 Office: (517) 355-9724 Lab: (517) 353-9125 FAX: (517) 353-9334 Email: rmgarav...@gmail.com **************************************************************** On Jun 12, 2012, at 10:46 PM, LISA wrote: > Hi all, > > My work is to solve huge complex containing 4 different proteins and total > molecular weight is about 300 KD. I can purify the complex by co-expression > them in E.coli. This complex contains 8 protein A, 2 protein B and 1 protein > C and D. protein B and protein C have homology structures deposited in PDB > database. No homology structure available for protein A and D, which > contribute 60% of the whole molecular weight for the complex. > > Now I am trying to find a way to solve the phase of this complex. I am > thinking of use sad or mad with se-Met. There total 111 Met residues in > this complex. Is it possible to solve this complex by se-Met? Does someone > have experience to solve huge complex structure with se-met? It is also very > welcome for all the suggestion. Thank you. > > All the best, > > Lisa
