Fig. 2. (A) Stereoview of the 20 minimum energy structures. The superposition has been obtained using the structurally conserved regions (SCRs) as defined previously in Barbato et al. (1999). The inhibitor α–C atoms are shown in red. The N–terminal 21 residues were not included in the structure calculations, since their conformation is ill defined. (B) Molscript (Kraulis, 1991) representation of the NS3 protease domain, the chymotrypsin-like common SCRs are coloured in blue and the structural element labels follow the chymotrypsin-like nomenclature. The residues forming the secondary structural elements are: strands A1 (34–37), B1 (41–44), C1 (51–55), D1 (63–66), E1 (69–78), F1 (82–86), A2 (104–108), B2 (122–126), C2 (141–145), D2 (150–152), E2 (155–159), F2 (166–170); helices α1 (55–59), α2 (132–136), α3 (173–180).