Superposition of 3D structures of proline iminopeptidases 1WM1 (yellow) and 1MTZ (green), and esterase 2UZ0 (purple). The structure of 1AZW is highly similar to 1WM1 and is not shown. A) The 4 conserved structural core segments are shown as thick tubes, and the variable segments as thin sticks connecting C-alpha atoms. The variable large cap regions of the peptidases, which do not superpose, are at the bottom half of the figure. Note that the esterase has a much shorter connecting segment in this cap region. The red frame indicates the position of the active site, which is shown as the zoomed-in view in Panel B. B) The catalytic site is shown with catalytic residues Ser, His and Asp. The active site is enlarged and rotated by about 180 degrees relative to Panel A. A short stretch of the cap region in both peptidases is shown, bearing the Glu residues that interact with the positive charge of the peptide substrate N-terminus. Note that the side chains of the two Glu residues superpose very well, despite coming from different (non-superposable) parts of the cap region.
Liu et al. BMC Genomics 2010 11:36 doi:10.1186/1471-2164-11-36