Structural superposition of the ancestral core in pancreatic lipase and patatin. 3D structures of the conserved core module (see Figure 2) from pancreatic lipase 1N8S  (A, segments 68–77, 144–166, 170–176), patatin 1OXW  (C, segments 28–37, 70–87, 148–158) and a superposition of both (B). The module starts with a β-strand (β-2) that is followed by another β-strand (β-1), an α-helix (α+1) and a β-strand (β+1). Numbers in parentheses indicate the relative positions to the nucleophilic elbow in the protein sequence. This loop is crucial for catalytic activity and typically contains a catalytic serine. It is located between the adjacent secondary structure elements β-1 and α+1. The connections to the other β-strands (β-2 and β+1) are not direct and can include longer stretches of additional secondary structure.
Schneider et al. BMC Bioinformatics 2006 7:164 doi:10.1186/1471-2105-7-164