Genital Chlamydia trachomatis! (CT) infections are a major public health concern that can adversely affect reproductive health and neonate survival. Interferon gamma (IFNg) is proposed to protect against CT infection by inducing the tryptophan catabolizing enzyme indoleamine 2,3-dioxygenase 1 (IDO1). The ensuing depletion of tryptophan starves CT of this essential amino-acid leading to bacterial eradication. By expressing the chlamydial enzyme tryptophan synthase (TS), genital serovars of CT can escape the effects of IFNg if the microbial metabolite indole is present in the infection microenvironment. TS can salvage indole within the chlamydial inclusion to generate tryptophan. TS expression is tightly regulated by the tryptophan operon repressor (TrpR), which permits transcription of the operon only when tryptophan is absent. We recently discovered that indole derivatives produced by the gut microbiome, termed TrpR de-repressors, rapidly induce the expression of chlamydial TS. Further, when TS is expressed in the absence of indole, the enzyme rapidly deaminates serine to generate ammonia (NH3), a known bactericidal compound. While evaluating the effect of TrpR de-repressors on different chlamydial serovars, we discovered that although de-repression was equally efficient between them, the production of NH3 varied dramatically. Using a combination of approaches, here we propose to: 1) Identify methods by which CT can assimilate NH3 produced by TS; and 2) Determine whether sequence differences in TS between serovars determines their catalytic properties vis--vis ammonia generation. The outcome of our findings will permit the design of novel pharmacological approaches against chlamydial infection by augmenting the effect of protective host responses.
Genital Chlamydia trachomatis uses the chlamydial enzyme tryptophan synthase (TS) in combination with indole produced by the genital microbiome to evade protective host immune responses that starve the bacterium of tryptophan. This study builds on our recent discovery that TS can catalyze an alternative ammonia generating reaction that kills genital Chlamydia trachomatis, by biochemically determining how sequence variations in TS dramatically alter its ammonia generating activity, and by identifying mechanisms used by Chlamydia trachomatis to evade the bactericidal effects of TS-generated ammonia. Study outcomes will inform the development of molecular therapeutics targeting TS to augment natural immunity against this major STI pathogen.
