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Hi everyone, what could it be a fo-fc electron density blob at around 1.44 A to the ND1 of a His? Below there is the 2fo-fc at 1.1 sigma and fo-fc at 3 sigma, with canonical His and with ND1 methylated histidine. In theory it could fit but I have never heard of such an His modification for a protein produced in E. coli. In PDB this modified His (MHS) was found only in METHYL-COENZYME M REDUCTASE (as far as I know). The blob remains for all the refinement and the fo-fc map is generally clean. Is it really a modified His, could it be some kind of radiation damage, something else? Thank you, Bye, roberto.