TRIM21 is a trimeric protein that binds IgG Fc via the B30.2 domain.
TRIMs comprise a large protein family that include anti-retroviral restriction factors such as TRIM5alpha. Auto-antibodies to TRIM21 (Ro52) are a common serological feature of patients with Sjogren's syndrome and systemic lupus erythematosus ( SLE). We show that, in addition to this autoantibody response, TRIM21 binds specifically to the Fc region of human IgG isotypes 1, 2 and 4, via a conformation dependent interaction. The minimal binding epitope was identified as the C-terminal B30.2 domain. The interaction was independent of N-linked glycosylation of the IgG CH2 domain. TRIM21 formed a trimer that competed with protein A for binding to IgG Fc. We conclude that TRIM21 binds to the consensus CH2/CH3 domain interface in the Fc region, overlapping the binding site of several other proteins, including Staphylococcus aureus protein A and Streptococcus spp. protein G. The data suggest that the normal function of TRIM21 involves regulation of IgG functions and that TRIM/B30.2 molecules may have broader and unsuspected roles in innate immunity, beyond that of retroviral restriction.[1]References
- TRIM21 is a trimeric protein that binds IgG Fc via the B30.2 domain. Rhodes, D.A., Trowsdale, J. Mol. Immunol. (2007) [Pubmed]
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