Substrate-binding mode of Pro21717-CD.

<p>(A) Stereoview of the substrate-binding site in Pro21717-CD. The bound, co-purified peptide (magenta) facilitated the characterization of the substrate-binding pocket and the substrate-binding mode of Pro21717. The side chains of the catalytic triad (Asp185, His244, and Ser425) and the residues in the nearby S2 and S4 pockets are presented as a stick model. (B) Ribbon diagram showing superposition of Pro21717-CD (orange) and Carlsberg subtilisin (cyan) at the active site. The A–A–P–F peptide in Pro21717-CD and the A–C–T–L peptide in subtilisin Carlsberg are shown as sticks. The catalytic triad residues Asp185, His244, and Ser425 (Pro21717-CD) and Asp32, His64 and Ser221 (subtilisin Carlsberg) are also shown as sticks. (C) Schematic view of the A–A–P–F peptide-binding mode in Pro21717-CD. The key hydrogen and hydrophobic interactions involved in peptide binding are presented using Ligplot.