HERC5 was also ADP-ribosylated by S. flexneri effector OspC1 at Arg44
As reported, ADP-riboxanation (524.03 Da) involves an additional deamidation upon the conventional ADP-ribosylation (541.06 Da) (Figure 3c; Li et al., 2021; Peng et al., 2022). Indeed, ADP-ribosylated peptide was detected in our MS/MS data, which indicated that S. flexnerieffector OspC1 could also ADP-ribosylated HERC5 at Arg44 (Figure 3a). Quantitative analysis suggested that the ratio of ADP-ribosylation and ADP-riboxanation of HERC5 at Arg44 was about 1:10 (Figure 3b). The same phenomenon was also observed by previous investigators, but the ratio they observed is much lower (1:1000) (Peng et al., 2022). In that study, the trace amount of ADP-ribosylated caspase-3 at Arg207 was interpreted as the intermediate of ADP-riboxanated caspase-3 catalyzed byChromobacterium violaceum CopC (Peng et al., 2022). However, based on our result, we tend to believe that the additional deamidation is reversible and the ADP-ribosylated HERC5 at Arg44 is the product of the reversible reaction from ADP-riboxanated HERC5 (Figure 3c). Unfortunately, there is still no further experimental evidence to support our hypothesis.