Fig. 4

Bacterial avidins may be expressed as fusion proteins together with a pepsin-like aspartyl protease. a Multiple sequence alignment of the putative aspartyl protease domain of bacterial avidin sequences with the aspartyl proteases pepsin (Sus scrofa, PDB ID: 4PEP, [75]), cathepsin D (Camelus dromedarius, PDB ID: 4AA9, [82]) and chymosin (Ixodes ricinus, PDB ID: 5N71, [83]). The aspartic acid (asparagine in cathepsin D) residues of the putative active site are highlighted with red arrowheads [84]. b Multiple sequence alignment of the putative avidin domain of bacterial avidin sequences with streptavidin (Streptomyces avidinii, PDB ID: 3RY2, [76]), chicken avidin (Gallus gallus, PDB ID: 1VYO, [85]) and rhizavidin (Rhizobium etli, PDB ID: 3EW1, [53]). Multiple sequence alignment of the putative avidin domain of bacterial avidin sequences with streptavidin, chicken avidin and Xenopus avidin (xenavidin). Both alignments were carried out with T-Coffee in the Expresso mode (http://tcoffee.crg.cat/; [70, 80, 81]). c Schematic picture showing the domain organization of the putative protease-avidin fusion proteins. d Homology model of Oleiagrimonas soli protease-avidin fusion protein, generated with Modeller 9.25 [74]. Swine pepsin (PDB ID: 4PEP; [75]) was used as a template for the protease domain, and streptavidin (PDB ID: 3RY2; [76]) for the avidin domain. The active site aspartic acid residues are shown in red