Fig. 4.

Disparate heterocycle synthetases accept substrates from related and distant prokaryotes. (A) The S. pyogenes synthetase SagBCD accepts the C. botulinum protoxin and produces a cytolytic toxin. (Left) Hemolytic assay. (Center and Right) Fluorescence microscopy and DIC images of HEK293a cells treated as indicated. (B) Hemolytic assay of SagA and ClosA treated with the synthetase complex from E. coli (McbBCD) and the hyperthermophile P. furiosus (PagBCD). Recombinant MBP-McbD must be first treated with thrombin (thr) before synthetase activity is observed.