Fig. 4

Aspartic protease of S. molnari – signal peptide peptidase. a Phylogenetic relationship of S. molnari SPPL (Sm_SPPL), (ML, 1000 bootstrap support values shown at nodes). b Predicted tertiary structure of Sm_SPPL according to Phyre2, showing nine transmembrane domains with active site highlighted in pink. c Closer view of active site and interacting residues. d Schematic of Sm_SPPL structure showing location of active sites and motifs within sequence