Equilibrium binding studies of recombinant anti-single-stranded DNA Fab. Role of heavy chain complementarity-determining regions

• Published in: The Journal of biological chemistry Vol. 271; no. 21; pp. 12241 - 12246
• Main Authors: Komissarov, A A, Calcutt, M J, Marchbank, M T, Peletskaya, E N, Deutsher, S L
• Format: Journal Article
• Language: English
• Published: United States 24-05-1996
• Subjects: Amino Acid Sequence; Animals; Binding Sites; DNA - immunology; DNA - isolation & purification; Immunoglobulin Fab Fragments - metabolism; Immunoglobulin Variable Region - immunology; Ligands; Mice; Molecular Sequence Data; Protein Binding; Spectrometry, Fluorescence
• ISSN: 0021-9258
• DOI: 10.1074/jbc.271.21.12241

We previously isolated nucleic acid-binding antibody fragments (Fab) from bacteriophage display libraries representing the immunoglobulin repertoire of automimune mice to expedite the analysis of antibody-DNA recognition. In the present study, the binding properties of one such anti-DNA Fab, high affinity single-stranded (ss) DNA-binding Fab (DNA-1), were defined using equilibrium gel filtration and fluorescence titration. Results demonstrated that DNA-1 had a marked preference for oligo(dT) (100 nM dissociation constant) and required oligo(dT) >5 nucleotides in length. A detailed analysis of the involvement of the individual heavy chain (H) complementarity-determining regions (CDR) ensued using previously constructed HCDR transplantation mutants between DNA-1 and low affinity ssDNA-binding Fab (D5), a Fab that binds poorly to DNA (Calcutt, M. J. Komissarov, A. A., Marchbank, M. T., and Deutscher, S. L. (1996) Gene (Amst.) 168, 9-14). Circular dichroism studies indicated that the wild type and mutant Fab studied were of similar overall secondary structure and may contain similar combining site shapes. The conversion of D5 to a high affinity oligo(dT)-binding Fab occurred only in the presence of DNA-1 HCDR3. Results with site-specific mutants in HCDR1 further suggested a role of residue 33 in interaction with nucleic acid. The results of these studies are compared with previously published data on DNA-antibody recognition.