PenB_CYSP gene and its transcript structure and PenB_CYSP protien homology based model. (A) Schematic representation of the PenB_CYSP gene and its transcript. Exons are represented by boxes, introns by lines; dark grey boxes denote 5′ and 3′ UTRs; light grey boxes denote the coding sequence. The black triangle indicates a bioinformatically identified polyadenylation signal. (B) Homology based model of PenB_CYSP protein. Model was build using I-Tasser server based on 7PCK template (left side). First 92 N terminal residues (orange) represent procathepsin variable region (thus this part of the model is the least reliable, mostly modeled on secondary structure and transmembrane helix restrains). This region contains putative signal peptide and transmembrane domain. Next, there is propeptide inhibitor domain I29 (cyan), residues 93–157. The rest of the protein constitute cathepsin peptidase C1 domain (grey). Boxed part of C1 domain enlarged on right contains catalytic dyad with important residues (red) and residues of S2 pocket (green) which is responsible for substrate specific binding.