Crystallization and preliminary X-ray diffraction analysis of a specific VHH domain against mouse prion protein

Prion disorders are infectious diseases that are characterized by the conversion of the cellular prion protein PrP^C into the pathogenic isoform PrP^Sc. Specific antibodies that interact with the cellular prion protein have been shown to inhibit this transition. Recombinant VHHs (variable domain of dromedary heavy-chain antibodies) or nanobodies are single-domain antibodies, making them the smallest antigen-binding fragments. A specific nanobody (Nb_PrP_01) was raised against mouse PrP^C. A crystallization condition for this recombinant nanobody was identified using high-throughput screening. The crystals were optimized using streak-seeding and the hanging-drop method. The crystals belonged to the orthorhombic space group P2₁2₁2₁, with unit-cell parameters a = 30.04, b = 37.15, c = 83.00 Å, and diffracted to 1.23 Å resolution using synchrotron radiation. The crystal structure of this specific nanobody against PrP^C together with the known PrP^C structure may help in understanding the PrP^C/PrP^Sc transition mechanism.