Rhodopseudomonas palustris grows photoheterotrophically on aromatic compounds available in aquatic environments rich in plant-derived
lignin.
Benzoate degradation is regulated at the transcriptional level in R. palustris in response to
anoxia and the presence of
benzoate and/or
benzoyl-CoA (Bz-
CoA). Here, we report evidence that anaerobic
benzoate catabolism in this bacterium is also regulated at the post-translational level. In this pathway,
benzoate is activated to Bz-
CoA by the
AMP-forming Bz-
CoA synthetase (BadA)
enzyme. Mass spectrometry and mutational analysis data indicate that residue Lys512 is critical to BadA activity. Acetylation of Lys512 inactivated BadA; deacetylation reactivated BadA. Likewise,
4-hydroxybenzoyl-CoA (
HbaA) and
cyclohexanecarboxyl-CoA (AliA)
synthetases were also reversibly acetylated. We identified one
acetyltransferase that modified BadA, Hba and AliA in vitro. The
acetyltransferase enzyme is homologous to the
protein acetyltransferase (Pat)
enzyme of Salmonella enterica sv Typhimurium LT2, thus we refer to it as RpPat. RpPat also modified
acetyl-CoA (Ac-
CoA)
synthetase (Acs) from R. palustris. In vivo data indicate that at least two deacetylases reactivate BadA(Ac). One is SrtN (encoded by srtN, formerly rpa2524), a
sirtuin-type
NAD(+)-dependent deacetylase (O-acetyl-
ADPribose-forming); the other deacetylase is LdaA (encoded by ldaA, for
lysine deacetylase A; formerly rpa0954), an
acetate-forming
protein deacetylase. LdaA reactivated Hba(Ac) and AliA(Ac)in vitro.