RESUMEN
Bacteria that colonize animals must overcome, or coexist, with the reactive oxygen species products of inflammation, a front-line defense of innate immunity. Among these is the neutrophilic oxidant bleach, hypochlorous acid (HOCl), a potent antimicrobial that plays a primary role in killing bacteria through nonspecific oxidation of proteins, lipids, and DNA. Here, we report that in response to increasing HOCl levels, Escherichia coli regulates biofilm production via activation of the diguanylate cyclase DgcZ. We identify the mechanism of DgcZ sensing of HOCl to be direct oxidation of its regulatory chemoreceptor zinc-binding (CZB) domain. Dissection of CZB signal transduction reveals that oxidation of the conserved zinc-binding cysteine controls CZB Zn2+ occupancy, which in turn regulates the catalysis of c-di-GMP by the associated GGDEF domain. We find DgcZ-dependent biofilm formation and HOCl sensing to be regulated in vivo by the conserved zinc-coordinating cysteine. Additionally, point mutants that mimic oxidized CZB states increase total biofilm. A survey of bacterial genomes reveals that many pathogenic bacteria that manipulate host inflammation as part of their colonization strategy possess CZB-regulated diguanylate cyclases and chemoreceptors. Our findings suggest that CZB domains are zinc-sensitive regulators that allow host-associated bacteria to perceive host inflammation through reactivity with HOCl. IMPORTANCE Immune cells are well equipped to eliminate invading bacteria, and one of their primary tools is the synthesis of bleach, hypochlorous acid (HOCl), the same chemical used as a household disinfectant. In this work, we present findings showing that many host-associated bacteria possess a bleach-sensing protein that allows them to adapt to the presence of this chemical in their environment. We find that the bacterium Escherichia coli responds to bleach by hunkering down and producing a sticky matrix known as biofilm, which helps it aggregate and adhere to surfaces. This behavior may play an important role in pathogenicity for E. coli and other bacteria, as it allows the bacteria to detect and adapt to the weapons of the host immune system.
Asunto(s)
Adhesión Bacteriana/genética , Biopelículas/crecimiento & desarrollo , GMP Cíclico/análogos & derivados , Proteínas de Escherichia coli/genética , Escherichia coli/genética , Regulación Bacteriana de la Expresión Génica , Inflamación/genética , Transducción de Señal , Bacterias/clasificación , Bacterias/genética , Bacterias/inmunología , Bacterias/metabolismo , Adhesión Bacteriana/inmunología , Biopelículas/efectos de los fármacos , GMP Cíclico/genética , GMP Cíclico/metabolismo , Escherichia coli/efectos de los fármacos , Escherichia coli/inmunología , Escherichia coli/metabolismo , Proteínas de Escherichia coli/inmunología , Proteínas de Escherichia coli/metabolismo , Genoma Bacteriano , Ácido Hipocloroso/farmacología , Inflamación/inmunologíaRESUMEN
Quantum mechanical calculations reveal the preferred mechanism and origins of chemoselectivity for HOCl-mediated oxidation of zinc-bound thiolates implicated in bacterial redox sensing. Distortion/interaction models show that minimizing geometric distortion at the zinc complex during the rate-limiting nucleophilic substitution step controls the mechanistic preference for OH over Cl transfer with HOCl and the chemoselectivity for HOCl over H2 O2 .
