Figure 2. Known and predicted structures of cystatins. The known structures of oryzacystatin (1EQK.pdb) (Panel A), chicken egg white cystatin (CEW1.pdb) (Panel C), and the predicted structures of C. elegans RO1B10.1 (Panel B) and human cystatin S (Panel D) are shown. The alignment in Fig. 1 was the basis for homology modeling by means of Deep View (SWISS-MODEL; Guex and Peitsch, 1997). The prominent -helix 1 is positioned in the center of all four structures, and the -2/loop region (absent in oryzacystatin) above. The conserved G, QXVXG, and PW regions, and the two disulfide bonds (SS1 is N-terminal, SS2 is C-terminal), are labeled on the chicken cystatin structure, and shown as space-filling atoms in all structures where present. The legumain inhibition region N39 (Leg) is also indicated on chicken cystatin.