Thank you all for your responses. I already have a few ideas about how to approach the problem.
One of my concerns with so monomers per asymmetric unit at lower resolution was the failure of MR software. Neither PHENIX nor Phaser MR have made progress. I am fairly new to anomalous methods, having solved only two structures by SeMet-based SAD. I've certainly picked up on a number of tricks from the recent messages on heavy atoms, but I thought my case might be a little unusual. I am confident the space group is P1, as it was the only viable option when I indexed four clean albeit low-res datasets. The monomers are ~38 kDa, and the crystals diffracted to 3.4-3.0 at a synchrotron. The conditions for both native and SeMet crystals are: 8-12% PEG 2000 MME, 0.2 M ammonium sulfate, 0.1 M sodium acetate pH 5.5. Macromolecular seeding of native crystals into SeMet drops yields the needle-like crystals. Any further input is greatly appreciated! Regards, Chris On Sat, Jan 18, 2014 at 11:14 AM, Chris Fage <cdf...@gmail.com> wrote: > Hello Everyone, > > I am currently trying to phase a structure with an asymmetric unit > predicted to contain 20-24 monomers (space group P1). The native crystals, > while beautiful in appearance (see attached), only diffract to ~3.4-3.0 > angstroms at best, and SeMet-derived crystals grow with poor morphology > (small needles). Also, based a fluorescence scan, I know that mercury does > not bind appreciably. Other than screening for a new space group, what > options might I have for phasing this many monomers at lower resolution? Is > there any real chance of solving the structure in this space group? > > Thank you in advance for any suggestions! > > Regards, > Chris >
