Importance of a CDR H3 Basal Residue in VH/VL Interaction of Human Antibodies

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Abstract
Although the cooperativity of the VH and VL domains of an antibody in antigen binding has been extensively studied, the interaction between the VH and VL domains had not received sufficient attention. To systematically investigate the relationship between the amino acid sequence and VH/VL interaction strength, we here used a set of anti-bovine serum albumin antibodies having a single human framework for VH (V3-23/DP-47 and JH4b) and Vk (O12/O2/DPK9 and Jkl), but with different VH/VL interaction strengths. By phage display of a VH mini-library and analysis of the interaction of amino acids with immobilized VL fragments, the residue at H95 (Kabat numbering) at the beginning of seven CDR H3 residues was found to play a key role in determining the VH/VL interaction. On saturation mutagenesis of H95, Gly showed the strongest interaction, while Asp, Asn, and Glu showed lesser interaction in that order. The generality of the rule was confirmed by the test with urine-derived human L chain instead of a particular VL. The results demonstrate that H95 plays a central role in deciding the VH/VL interaction of human Fvs that have most commonly found frameworks.

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