A Germline-Encoded Structural Arginine Trap Underlies the Anti-DNA Reactivity of a Murine V Gene Segment

• Published in: International journal of molecular sciences 2021-04, Vol.22 (9), p.4541
• Main Authors: Dos Santos Araújo, Ronny Petterson, França, Renato Kaylan Alves, Valadares, Napoleão Fonseca, Maranhão, Andrea Queiroz, Brigido, Marcelo Macedo
• Format: Article
• Language: English
• Subjects: anti-DNA; Antibodies; Antigens; Autoantigens; Autoimmunity; autoreactivity; B cell’s repertoire; Binding sites; Bone marrow; Chains; Cloning; Complementarity-determining region 3; Deoxyribonucleic acid; DNA; DNA shuffling; Genes; Hydrogen bonds; Immunology; Lymphocytes B; pre-BCR; Reactivity; Segments; Structural members; V genes
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms22094541

Autoimmunity may have its origins of early repertoire selection in developmental B cells. Such a primary repertoire is probably shaped by selecting B cells that can efficiently perform productive signaling, stimulated by self-antigens in the bone marrow, such as DNA. In support of that idea, we previously found a V segment from V 10 family that can form antibodies that bind to DNA independent of CDR3 usage. In this paper we designed four antibody fragments in a novel single-chain pre-BCR (scpre-BCR) format containing germinal V gene segments from families known to bind DNA (V 10) or not (V 4) connected to a murine surrogate light chain (SLC), lacking the highly charged unique region (UR), by a hydrophilic peptide linker. We also tested the influence of CDR2 on DNA reactivity by shuffling the CDR2 loop. The scpre-BCRs were expressed in bacteria. V 10 bearing scpre-BCR could bind DNA, while scpre-BCR carrying the V 4 segment did not. The CDR2 loop shuffling hampered V 10 reactivity while displaying a gain-of-function in the nonbinding V 4 germline. We modeled the binding sites demonstrating the conservation of a positivity charged pocket in the V 10 CDR2 as the possible cross-reactive structural element. We presented evidence of DNA reactivity hardwired in a V gene, suggesting a structural mechanism for innate autoreactivity. Therefore, while autoreactivity to DNA can lead to autoimmunity, efficiently signaling for B cell development is likely a trade-off mechanism leading to the selection of potentially autoreactive repertoires.