Deciphering Molecular Mechanism of Silver by Integrated Omic Approaches Enables Enhancing its Antimicrobial Efficacy in E. Coli

Abstract

Despite the broad-spectrum antimicrobial activities of silver, its internal usage is restricted owing to the toxicity. Strategies to enhance its efficacy are highly desirable but rely heavily on the understanding of its molecular mechanism of action [1]. Silver has long been deemed to bind thiols in enzymes and thereby inactivates their functions, however, up to now, no direct silver-targeting proteins have been mined at a proteome-wide scale owing to the lack of appropriate techniques, which hinders systemic studies on the biological pathways interrupted by silver [2]. Herein, we build up a unique system, namely LC-GE-ICP-MS, and mapped out Ag+-binding proteins (Ag+-proteome) in E. coli for the first time. By using integrated omic approaches including metalloproteomics, metabolomics, bioinformatics and systemic biology, we delineated the first dynamic antimicrobial actions of Ag+, i.e., it primarily damages multiple enzymes in glycolysis and TCA cycle, leading to the stalling of the oxidative branch of the TCA cycle and an adaptive metabolic divergence to the reductive glyoxylate pathway. It then further damages the adaptive glyoxylate pathway and suppresses the cellular oxidative stress responses, causing systemic damages and death of the bacterium [3]. The silver-targeting residues in the identified proteins were further illustrated by crystal structures of silver-bound GAPDH and MDH at the atomic level [4]. Based on the molecular mechanism derived from our investigation, the therapeutic effect of Ag+ could be enhanced by supplementation of metabolites from TCA cycle and glycolysis, thereby reducing its dosage. Our mouse model of E. coli infection successfully demonstrates a proof-of-principle that fundamental knowledge and molecular understanding of silver stress can be translated into new antibacterial approaches in clinic. Our study resolves long-standing questions on how Ag+ exerts its antimicrobial activity at the molecular level and may also open up new horizons for in-depth exploration of silver (and nanosilver) toxicology in other bacteria. The integrated omic approaches approach we describe here can be widely applied to explore the molecular targets and mechanisms of action of other metal-based antimicrobial and anticancer drugs, and thereby facilitating the development of new therapeutics [5].