I am refining a pretty high resolution structure (1.65Å, P1) with two tetramers of the protein in the ASU using Phenix dev 1630.

Refinement statistics looks really good, R=0.16 Rf=0.18, maps are very clear. However, several sulphur atoms of the protein, and in particular the phosphorous atoms of its cofactor NAD have inflated B-factors, along with distinct FoFc peaks. For instance B-factors for a Met with very well defined density: CB=19.7, CG=27.5, SD=62.2, CE=38.4

For some of the residues it is comparable when I refine with or without TLS groups. I used one group per chain of this compact protein, the cofactor is part of each TLS group. Restraints for NAD were generated via eLBOW. When I refine the structure in refmac, using either the standard cif file or the eLBOW generated one, B-factors remain low.

Any ideas? I am happy to share the data. It is a SSGCID target and will be in the PDB shortly anyway.

Thanks,

Jan