Alkyl gallates inhibit serine O-acetyltransferase in bacteria and enhance susceptibility of drug-resistant Gram-negative bacteria to antibiotics

Front Microbiol. 2023 Oct 27:14:1276447. doi: 10.3389/fmicb.2023.1276447. eCollection 2023.

Abstract

A principal concept in developing antibacterial agents with selective toxicity is blocking metabolic pathways that are critical for bacterial growth but that mammalian cells lack. Serine O-acetyltransferase (CysE) is an enzyme in many bacteria that catalyzes the first step in l-cysteine biosynthesis by transferring an acetyl group from acetyl coenzyme A (acetyl-CoA) to l-serine to form O-acetylserine. Because mammalian cells lack this l-cysteine biosynthesis pathway, developing an inhibitor of CysE has been thought to be a way to establish a new class of antibacterial agents. Here, we demonstrated that alkyl gallates such as octyl gallate (OGA) could act as potent CysE inhibitors in vitro and in bacteria. Mass spectrometry analyses indicated that OGA treatment markedly reduced intrabacterial levels of l-cysteine and its metabolites including glutathione and glutathione persulfide in Escherichia coli to a level similar to that found in E. coli lacking the cysE gene. Consistent with the reduction of those antioxidant molecules in bacteria, E. coli became vulnerable to hydrogen peroxide-mediated bacterial killing in the presence of OGA. More important, OGA treatment intensified susceptibilities of metallo-β-lactamase-expressing Gram-negative bacteria (E. coli and Klebsiella pneumoniae) to carbapenem. Structural analyses showed that alkyl gallate bound to the binding site for acetyl-CoA that limits access of acetyl-CoA to the active site. Our data thus suggest that CysE inhibitors may be used to treat infectious diseases caused by drug-resistant Gram-negative bacteria not only via direct antibacterial activity but also by enhancing therapeutic potentials of existing antibiotics.

Keywords: CysE inhibitors; alkyl gallates; antimicrobial resistance; cysteine; persulfides; serine O-acetyltransferase.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was supported in part by Grants-in-Aid for [(S), (B), (C), Transformative Research Areas (A), Challenging Exploratory Research] from the Ministry of Education, Science, Sports, and Technology (MEXT), Japan (21H02071 and 21H05267) to TSa, (20K21496 and 21H05263) to TA, and (22K05443) to KO, a research grant from the Association for Research on Lactic Acid Bacteria to TSa, the Japan Society for the Promotion of Science (JSPS) International Research Fellowship to TZ, the Program for Leading Graduate Schools, HIGO (Health Life Science: Interdisciplinary and Global Oriented) Program, Kumamoto University, Japan to (AR), Japan Agency for Medical Research and Development (AMED), Japan (17fm0208029h0001) to TSh, and the Japan Science and Technology Agency (JST), CREST, Japan (JPMJCR2024) to TA.