Dehomocysteinylation is catalysed by the sirtuin‐2‐like bacterial lysine deacetylase CobB

Hyperhomocysteinemia, which is characterised by elevated blood levels of the non-protein amino acid homocysteine (Hcy), is an independent risk factor for many diseases, including cardiovascular diseases, neurodegenerative diseases and birth defects. The incorporation of homocysteine into proteins, known as protein N-homocysteinylation, has been considered a major mechanism that contributes to hyperhomocysteinemia. However, the process of dehomocysteinylation, N-homocysteinylation substrates and regulatory enzyme(s), remain largely unknown. In this study, we observed that the dehomocysteinylation reaction is a spontaneous process that can be inhibited by blocking –SH groups, which have been demonstrated to be critical for non-enzymatic dehomocysteinylation reactions. We also report that CobB, a known Sir2-like bacterial lysine deacetylase, catalyzes lysine dehomocysteinylation reactions both in vitro and in vivo. Our work provides insight into how this non-enzymatic modification might be removed from affected proteins, supplies potential targets for developing identification methods for N-Hcy-proteins, and identifies CobB as the first prokaryotic dehomocysteinylation enzyme. This article is protected by copyright. All rights reserved.