Fig. 6. Determining the effect of downstream A-domain rate on upstream C-domain peptide bond formation by varying the amino acid provided during the peptide bond forming step. Summary of the assay (left), in which peptide 4 was loaded onto PCP6 and used to reconstitute heptapeptide bond formation in the presence of the natural A-domain amino acid substrate Dpg, a substrate activated ∼2.5× more slowly (4-Hpg) and no amino acid substrate. Results (box on right) show that an increase in hydrolysed hexapeptide starting material (shown in yellow; residual PCP-bound hexapeptide shown in green) correlates to the presence of a poorer (or no) suitable A-domain substrate, with a decrease in extended peptide product (shown in blue).
