Hello again, and thank you for your quick replies!
For your consideration, I have added a representative .mtz and .pdb to my shared dropbox folder (https://www.dropbox.com/sh/2wdax5uqlb1f4m3/AABQlGK2_mgibtqnm61E-7o0a?dl=0).<https://www.dropbox.com/sh/2wdax5uqlb1f4m3/AABQlGK2_mgibtqnm61E-7o0a?dl=0> There are 22 monomers in the ASU, and this peak is present to some degree in all of them, but is strongest for chain L. These monomers are very similar to the ERAP1 structure PDB ID 2yd0. Napo and Tushar: The resolution limit is 3.26 angstroms. The crystallization condition is ammonium sulfate and MES. There will also be a little HEPES and DMSO (from the sample buffer). The cryoprotectant is saturated lithium sulfate. There is also an inhibitor in the drop but this positive density is present in all my datasets, each with different inhibitors, so I don't think this is a bound inhibitor. The Trp B-factors are not out of place for this structure. Tristan: You make a good point, I have built other sulfates into the model and this may account for some of the positive density near this asparagine. I will try this. Thank you for your suggestion. Best, Zach Stern Lab Pathology Department University of Massachusetts Medical School
