3.4.21.113 crystal structure of inhibitors bound to the protease, show close interaction of the macrocycle with the Ala156 methyl group and S4 pocket 669812 3.4.21.113 crystal structure of SCH446211 bound to NS3/NS4A. The P1 (S)-diastereomer is the active component. A reversible covalent bond is formed between the enzyme active site serine (Ser139) hydroxyl and the ketone carbonyl of the inhibitor. The resulting oxygen anion is stabilized by hydrogen bonding with His57. P3 tert-butyl glycine makes hydrophobic contact with the S3 pocket. The NH of the P3 carbamate and the carbonyl at P3 make H bonds with Ala-157. The P2 dimethyl-cyclopropyl proline adopts a bent conformation, placing the two methyl groups in close proximity to Arg-155. The cyclopropyl alanine residue at P1 fits well in the shallow hydrophobic S1 pocket. The P1' glycine moiety does not H bond with the enzyme backbone but allows the P1-P2' residues to form a “C-clamp” that wraps around the side chain of lysine 136 for improved overall binding 688242 3.4.21.113 purified full-length CSFV NS3 with its NS4A PCS covalently tethered to its N terminus through a flexible linker, X-ray diffraction structure determination and analysis at 2.35 A resolution 754554 3.4.21.113 purified recombinant soluble CSFV NS4A37NS3 complex, X-ray diffraction structure determination and analysis at 3.05-3.21 A resolution 755207