Journal: Scientific Reports
Article Title: Reengineering the specificity of the highly selective Clostridium botulinum protease via directed evolution
doi: 10.1038/s41598-022-13617-z
Figure Lengend Snippet: Characterization of omLC/A cleavage. ( A ) Rates of SNAP cleavage by batch-expressed, purified qmLC/A and ( B ) omLC/A at the indicated DARET substrate concentrations (n = 3). ( C ) Deconvoluted ESI–MS of recombinant, full-length SNAP23 (fl-S23) treated with DTT and iodoacetamide to carbamidomethylate its six cysteines (6 × CAM). The mass spectrum of intact fl-S23 incubated with buffer (top, black) is compared to that of fl-S23 incubated with omLC/A (bottom, teal). Intact fl-S23 (1) and cleaved fl-S23 (cl. fl-S23, 2) peaks are labeled. Additional marked peaks correspond to the masses of peaks 1 and 2 plus one additional CAM (+ 57 Da), likely resulting from overalkylation by iodoacetamide . The cleaved peptide was not directly observed, but inferred from the mass difference of peaks 1 and 2. The deconvolution error is +/- 2 Da. ( D ) Recombinant omBoNT/A was purified by IMAC followed by anion exchange (AEX) chromatography. The omBoNT/A is ≈95% nicked upon DTT reduction as demonstrated by the presence of the HC/A and omLC/A bands. ( E ) In vitro cleavage of recombinant fl-S23 by two independent preparations of omBoNT/A (1 and 2) visualized with a C-terminal anti-SNAP23 antibody; before proteolysis, omBoNT/A was reduced with TCEP. The untreated, wtLC/A, and wtLC/E lanes provide negative controls. ( F ) In cellulo cleavage of SNAP23 and SNAP25 in SiMA-H1 cells infected with adenovirus delivering DNA encoding mCherry/SNAP23. Cells were treated with omBoNT/A or wtBoNT/A or without toxin (ct). Proteins, full-length (fl) or cleaved (cl), were identified by Western blotting with anti-SNAP23, -SNAP25, or -mCherry antibodies (M, MW marker). Full-length images of these gels with multiple exposures where necessary are shown in Fig. S12 and S13).
Article Snippet: Human SNAP23 in vitro cleavage was evaluated by incubating 30 μg of human recombinant SNAP23 protein (Novus Biologicals) with 400 nM of either wild-type LC/A, wild type LC/E, or reduced full length omBoNT/A at 37 °C for 1 h in PBS, pH 7.2 (ThermoFisher).
Techniques: Purification, Recombinant, Incubation, Labeling, Chromatography, In Vitro, Infection, Western Blot, Marker