Nanobodies

 

The occurrence of bona fide antibodies devoid of light chains in Camelidae was one of the major discoveries within our department. These so-called heavy-chain antibodies bind antigens solely with one single variable domain, referred to as VHH domain or Nanobody (Nb). Methods were developed to clone the VHH repertoire of an immunised dromedary (or llama) in phage display vectors, and to select the antigen-specific VHHs from these 'immune' VHH libraries. Recombinant Nanobodies are small (15kDa) and strictly monomeric. They bind the target with nM affinity, are stable and easy to manipulate. Moreover, the Nanobodies often bind to epitopes that are less immunogenic for conventional antibodies, such as the active sites of enzymes. Due to their small size, they also target areas that are not accessible to standard antibodies. Another advantage is that they generally bind conformational epitopes and that they are well expressed in bacterial expression systems so that they are cheaper and easier to produce in all kind of formats than standard monoclonal antibodies.

 

 

Nanobodies as crystallization chaperones

By rigidifying flexible regions and obscuring aggregative surfaces, Nanobody complexes warrant conformationally uniform samples that are key to protein structure determination by X-ray crystallography. The elucidation of the first GPCR structure in its active state using conformationally selective Xaperones demonstrates the power of the Xaperone platform to speed up and reduce the cost of generating diffracting quality crystals of challenging targets. Xaperones are antigen binding fragments from heavy chain only antibodies that:
 

  • bind cryptic epitopes and lock proteins in unique native conformations
  • increase the stability of soluble proteins and solubilized membrane proteins
  • reduce the conformational complexity of soluble proteins and solubilized membrane proteins
  • increase the polar surface enabling the growth of diffracting crystals
  • allow to affinity-trap active protein