Determination of the X-ray structure of the snake venom protein omwaprin by total chemical synthesis and racemic protein crystallography

摘要

The 50-residue snake venom protein l-omwaprin and its enantiomer d-omwaprin were prepared by total chemical synthesis. Radial diffusion assays were performed against Bacillus megaterium and Bacillus anthracis; both l- and d-omwaprin showed antibacterial activity against B. megaterium. The native protein enantiomer, made of l-amino acids, failed to crystallize readily. However, when a racemic mixture containing equal amounts of l- and d-omwaprin was used, diffraction quality crystals were obtained. The racemic protein sample crystallized in the centrosymmetric space group P21/c and its structure was determined at atomic resolution (1.33 Å) by a combination of Patterson and direct methods based on the strong scattering from the sulfur atoms in the eight cysteine residues per protein. Racemic crystallography once again proved to be a valuable method for obtaining crystals of recalcitrant proteins and for determining high-resolution X-ray structures by direct methods.