Reversible Dimer Formation and Stability of the Anti-tumour Single-chain Fv Antibody MFE-23 by Neutron Scattering, Analytical Ultracentrifugation, and NMR and FT-IR Spectroscopy

• Published in: Journal of molecular biology Vol. 320; no. 1; pp. 107 - 127
• Main Authors: Lee, Yie Chia, Boehm, Mark K., Chester, Kerry A., Begent, Richard H.J., Perkins, Stephen J.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 28.06.2002
• Subjects: 1H NMR spectroscopy; Amino Acid Sequence; analytical ultracentrifuge; Antineoplastic Agents - chemistry; Antineoplastic Agents - metabolism; Dimerization; Humans; Immunoglobulin Fragments - chemistry; Immunoglobulin Fragments - metabolism; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Sequence Data; neutron scattering; Neutrons; Protein Structure, Quaternary; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - metabolism; Sequence Alignment; single-chain Fv antibody; size-exclusion chromatography; Spectroscopy, Fourier Transform Infrared; Temperature; Ultracentrifugation; neutron scattering; size-exclusion chromatography; scFv, single-chain Fv; single-chain Fv antibody; CEA, carcinoembryonic antigen; analytical ultracentrifuge; 1H NMR spectroscopy; FT-IR, Fourier transform infrared
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/S0022-2836(02)00403-5

MFE-23 is a single chain Fv (scFv) antibody molecule used to target colorectal cancer through its high affinity for the tumour marker carcinoembryonic antigen (CEA). ScFv molecules are formed from peptide-linked antibody V H and V L domains, and many of these form dimers. Our recent crystal structure for MFE-23 showed that this formed an unusual symmetric back-to-back association of two monomers that is consistent with a domain-swapped diabody structure. Neutron scattering and modelling fits showed that MFE-23 existed as compact V H–V L-linked monomers at therapeutically relevant concentrations below 1 mg/ml. Size-exclusion gel chromatography showed that the monomeric and dimeric forms of MFE-23 could be separated, and that the proportions of these two forms depended on the starting MFE-23 concentration. Sedimentation equilibrium experiments by analytical ultracentrifugation at nine concentrations of MFE-23 indicated a reversible monomer–dimer self-association equilibrium with an association constant of 1.9×10 3–2.2×10 3 M −1. Sedimentation velocity experiments using the time derivative g( s ∗) method showed that MFE-23-His has a concentration-dependent weight average sedimentation coefficient that increased from 1.8 S for the monomer to about 3–6 S for the dimer. Both values agreed with those calculated from the MFE-23 crystal structure. In relation to the thermal stability of MFE-23, denaturation experiments by 1H NMR and FT-IR spectroscopy showed that the molecule is stable up to 47 °C, after which denaturation was irreversible. MFE-23 dimerisation is discussed in terms of a new model for diabody structures, in which the V H and V L domains in the monomer are able to dissociate and reassociate to form a dimer, or diabody, but in which symmetric back-to-back contacts between the two monomers are formed. This dimerisation in solution is attributed to the complementary nature of the C-terminal surface of the MFE-23 monomer. Crystal structures for seven other scFv molecules have shown that, while the contact residues for symmetric back-to-back dimer formation in MFE-23 are not fully conserved, in principle, back-to-back contacts can be formed in these too. This offers possibilities for the creation of other forms of scFv molecules.