1YC7

Antigen Binding and Solubility Effects upon the Veneering of a Camel VHH in Framework-2 to Mimic a VH.

(2005) J Mol Biol 350: 112-125

• PubMed: 15913651 Search on PubMed
• DOI: https://doi.org/10.1016/j.jmb.2005.04.050
• Primary Citation of Related Structures:  
  1YC7, 1YC8, 1YZZ


• PubMed Abstract: 
  

  Heavy chain only antibodies of camelids bind their antigens with a single domain, the VHH, which acquired adaptations relative to classical VHs to function in the absence of a VL partner. Additional CDR loop conformations, outside the canonical loop structures of VHs, broaden the repertoire of the antigen-binding site. The combined effects of part of the CDR3 that folds over the "former" VL binding site and framework-2 mutations to more hydrophilic amino acids, enhance the solubility of VHH domains and prevent VL pairing. cAbAn33, a VHH domain specific for the carbohydrate moiety of the variant surface glycoprotein of trypanosomes, has a short CDR3 loop that does not cover the former VL binding site as well as a VH-specific Trp47 instead of the VHH-specific Gly47. Resurfacing its framework-2 region (mutations Tyr37Val, Glu44Gly and Arg45Leu) to mimic that of a human VH restores the VL binding capacity. In solution, the humanised VHH behaves as a soluble, monomeric entity, albeit with reduced thermodynamic stability and affinity for its antigen. Comparison of the crystal structures of cAbAn33 and its humanised derivative reveals steric hindrance exerted by VHH-specific residues Tyr37 and Arg45 that prevent the VL domain pairing, whereas Glu44 and Arg45 are key elements to avoid insolubility of the domain.

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Organizational Affiliation: 

Laboratorium voor Cellulaire en Moleculaire Immunologie, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium. kconrath@vub.ac.be