Structural and biochemical insights into His-tag-induced higher-order oligomerization of membrane proteins by cryo-EM and size exclusion chromatography

•Analysis of His10-tagged membrane proteins AdiC and GPR by size exclusion chromatography (SEC) reveals formation of non-physiological higher-order oligomers.•SEC experiments demonstrate that higher-order oligomer formation is mediated by His-tags and mainly depends on tag length.•Single particle cryo-EM analysis offers structural insights into the three-dimensional arrangement of higher-order oligomers and their interactions via His-tags.•Higher-order oligomers are identified as tetrameric AdiC as well as decameric and pentadecameric GPR assemblies.