Imaging of the Cytosolic Antibody Receptor TRIM21

Abstract: TRIM21 is a cytosolic ubiquitin ligase and an antibody receptor that providesa last line of defense against invading pathogens. By utilizing the diversity ofantibody repertoire to identify pathogens, TRIM21 serves as a link betweenintrinsic cellular defense and adaptive immunity. A variety of diseases havebeen linked to mutations of the TRIM family, including cancer, inflammatorydiseases, and autoimmune diseases. In this project, TRIM21 was producedand purified from Escherichia coli, (E.coli). Protein characterization wasperformed with SDS-PAGE, size exclusion chromatography and cryo-electronmicroscopy (cryo-EM). Previously TRIM21 has been shown to form a dimerwhen produced in SF9. Results from size exclusion chromatography show thatTRIM21 form a larger complex when expressed in E.coli. Cryo-EM resultsshow that the complex structure is more globular than previously thought.Purified TRIM21 was bound to the antibody IC100. SDS-PAGE and sizeexclusion chromatography results show much lower affinity to antibodies thanexpected.