Hello all,
crystals with high solvent content tend to diffract poorly, at least according to intuition. Several years ago we solved a structure that appeared to buck that trend with a solvent content of ≈0.8 and resolution beyond 2 Å, per merging statistics and visibility of spots on diffraction images.
I would welcome my colleagues’ opinions as to why I might observe the following:

1. Paired refinement (similar to Fig. 1 in Karplus&Diederichs) indicates that adding any higher resolution data beyond 3.4 Å, the lowest high resolution cut-off limit I tried, does not improve R-factors at the common lower resolution cutoff. Yes, diffraction is anisotropic in this case, but seemingly not to that extent. I hesitate to “throw out” all data beyond 3.4 Å, or whatever lower resolution cut-off I might try.
2. The Fo-Fc map, when countoured at ± 3 rmsd, includes many more (uninterpretable) features than I would expect after refinement to residuals in the mid-to-lower twenties. For expected map appearance, I had to crank up the coutour level to > 5 rmsd, like in the attached screenshot of the ADP·Mg⁺⁺ omit map.

Could these observations be linked to the high solvent content? (1) A high solvent content structure has a higher-than-average observation-to-parameter ratio, sufficiently high even when limited to stronger, low-resolution reflections? (2) Map normalization may not be attuned to such high solvent content?
I am interested in analyzing the automated decision-making of the PDB-REDO of this entry, such as paired refinement results and selection of ADP model. Should I find this information in the “All files (compressed)” archive? The “fully optimized structure’ shows ANISOU cards and NUMBER OF TLS GROUPS : NULL. Does this mean that individual ADPs have been refined anisotropically?
Looking forward to your insights,
Wolfram Tempel