Sadly, I have seen numerous examples of reasonably-sized crystals that give no observable ordered diffraction (I shot a few this weekend, in fact). I can’t give you evidence for what is happening, but I guess that you can build a macroscopic assembly using lattice interactions that are only modestly specific, resulting in a structure that is highly disordered internally, even though it looks OK visually (the jello model). Alternatively, you may have a crystal that was originally well-ordered but subsequently decayed; however, it failed to dissolve because proteins at the surface became cross-linked and held everything together (the soup dumpling model).
So no suggestions as how to proceed (except to follow Eddie’s sage advice to grow more/different crystals), but I can assure you that you’re not alone in observing this. Cheers, Pat Loll > On 21 Dec 2016, at 2:44 PM, Tom Huxford <thuxf...@mail.sdsu.edu> wrote: > > Dear ccp4b collective mind and experience, > > Greetings from San Diego. > > I have done my fair share of synchrotron data collection on many diverse > macromolecular crystal systems. But this weekend was the first time that I > ever shot crystals that failed to diffract entirely. > > Details: we have purified and crystallized an ~90 kDa proteolytic fragment > containing a single point mutant version of a myosin motor domain in complex > with a separate light chain polypeptide. The crystals are relatively small > (10-30 microns in each dimension) but clearly crystalline in character (clear > faces, edges, and facets). The crystals tested positive for protein by > absorbance at 280 nm. This weekend we tested more than 40 of them for > diffraction in different cryo solvents and did not observe a single > identifiable diffracted ray. It was as if we had only cryo on the end of our > loops. Increasing the time of exposure or annealing did nothing to improve > the situation. Crystals from a different protein system that we also tested > this weekend on the same beamline diffracted to beyond 1.3 Å. > > I only post this because, in my experience, crystals of this size and > superficial quality always give some signal--even if it is horrifyingly bad. > But never complete diffraction silence. We will work this week to identify > what it is that we "crystallized". But can anybody who has had a similar > experience suggest what it is that could be going on here? > > Thanks in advance for any responses. And happy holidays to us all. > > Tom Huxford. > ====================== > Tom Huxford. > Structural Biochemistry Laboratory > Department of Chemistry & Biochemistry > San Diego State University > (619) 594-1606 >
