CHAIN analysis of α,β-hydrolase fold constraints acting on prolyl oligopeptidases. See legend to Fig. 4 for descriptions. (A) Motif-based contrast hierarchical alignment. The bars directly below the displayed sequences indicate motifs with the narrow line indicating a deletion relative to that motif and wide bars indicating catalytic residues. (B) PSI-BLAST generated contrast hierarchical alignment. The histogram heights for the catalytic aspartate and histidine in this alignment are shorter in this figure because, unlike the motif-based alignment in (A), the PSI-BLAST algorithm assigns relatively stronger constraints to the nucleophilic catalytic residue (not shown) that is much easier to align correctly.