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.