Hello,

I am refining a few datasets of my protein of interest (ERAP1) bound to various inhibitors, and I repeatedly observe a positive density peak near an asparagine.  I first thought this might be a glycan, but this site does not fit the canonical N-linked glycosylation motif (this site sequence is NKL).  Previous crystal structures of this protein do not identify any ligand at this position.

https://www.dropbox.com/sh/2wdax5uqlb1f4m3/AABQlGK2_mgibtqnm61E-7o0a?dl=0

Asn833 positive density www.dropbox.com Shared with Dropbox

I would appreciate any suggestions of what this density might be.  Thank you for your help.

Best,

Zach Maben

Stern Lab

Pathology Department

University of Massachusetts Medical School