Effect of somatic mutation on DNA binding properties of anti-DNA autoantibodies

Autoantibodies that bind DNA are a hallmark of systemic lupus erythematosus. A subset Of autoantibody center dot DNA complexes localize to kidney tissue and lead to damage and even death. 11F8, 9F11, and 15B10 are clonally related anti-DATA autoantibodies isolated from an autoimmune mouse. F-11(8) binds ssDNA in a sequencespecific manner and causes tissue damage, while 9F11 and 15B10 bind ssDNA non-specifically and are benign. Among these antibodies, DNA binding properties are mediated byfive amino acid differences in primary sequence. Thermodynamic and kinetic parameters associated with recognition of structurally different DNA sequences were determined for each antibody to provide insight toward recognition strategies, and to explore a link between binding properties and disease pathogenesis. A model of 11F8 bound to its high affinity consensus sequenceprovides a foundation for understanding the differences in thermodynamic and kinetic parameters between the three mAbs. Our data suggest that 11F8 utilizes the proposed ssDNA recognition motif including V-Y32(L), a hydrogen bonding residue at V-91(L), and an aromatic residue at the tip of the third heavy chain complementarity determining region. Interestingly, a somatic mutation to arginine at V-31(H) in 11F8 may afford additional binding site contacts including V-R31(H), V-R96(H), and V-R98(H) that could determine specificity. (c) 2007 Wiley Periodicals, Inc.