Structural analysis of affinity maturation: the three-dimensional structures of complexes of an anti-nitrophenol antibody.
Affinity maturation of the immune response to nitrophenol-containing antigens has been extensively investigated. Significant strides made during the past several years with the advent of PCR technology have provided a wealth of biochemical knowledge. Structural investigations of the phenomena have however been limited. We have determined the three-dimensional structure of the Fab fragment of 88C6/12, an anti-4-hydroxy-3-nitrophenyl acetic acid antibody complexed with the immunizing hapten and with a heteroclitic iodinated hapten. The crystallographic structure of the complexes reveals that the binding is stabilized by a number of hydrogen bonds and extensive van der Waals interactions between the hapten and the antibody. In addition, the Fab binding pocket contains a region of positive electrostatic potential well suited for interaction with the predominant resonance form of the nitrophenyl ring system. The observed heteroclicity towards the iodinated hapten is not a direct result of iodine-protein interactions, but results from the enhanced stability in the iodinated ring of the resonance form that binds the antibody. In addition this investigation provides a rationale for the strong preference for the substitution in the heavy chain from the germ-line gene encoded Trp 33 to Leu 33 in the mature anti-nitrophenol response.
Department of Biophysics and Biophysical Chemistry, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA.
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Yuhasz
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Parry
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Amzel
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D000915:Antibody Affinity; D001483:Base Sequence; D003001:Cloning, Molecular; D006241:Haptens / Q000276:immunology*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics / Q000302:isolation & purification; D007147:Immunoglobulin Light Chains / Q000235:genetics / Q000302:isolation & purification; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D009596:Nitrophenols / Q000276:immunology*
D000911:Antibodies, Monoclonal; D006241:Haptens; D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D046911:Macromolecular Substances; D009596:Nitrophenols