Crystallization and preliminary diffraction study of hiv-1 protease complexed with hydroxyethylamine inhibitor si

refolded protein from inclusion bodies. A purification procedure comprising three chromatography steps yielded scFv 1696 in the purity necessary for crystallization trials. The complex was prepared by mixing scFv1696 with an excess of the epitope peptide corresponding to the N-terminus of HIV-2 PR (PQFSLWKR). Monomeric and dimeric forms of the complex were separated by FPLC on a Mono-Q column. In contrast to free scFv 1696 these forms are stable and do not interchange. In a series of crystallization trials crystals of the complex have been obtained. For crystallization trials by vapour diffusion method (hanging drop) only monomeric complex of the scFv1696 with epitope peptide was used. Crystals grew spontaneously at 25C in ammonium sulfate (concentrations: 1.8 2.0 M) at pH 4.6. These crystals were very sensitive and flaws on their surface appeared in few days. However, this spontaneous crystallization could not be reproduced with a new batch of the complex, therefore, a streak seeding technique was applied and single crystals of size up to 0.3 x 0.3 x 0.2 mm were obtained. Solving of 3D structure of the scFv 1696 epitope peptide complex is expected to lead to antibodystructurebased design of a new class of HIV protease non-active site inhibitors, possibly of different HIV resistance characteristics.