Increased Activity of Cystathionine β-Lyase Suppresses 2-Aminoacrylate Stress in Salmonella enterica.

Reactive enamine stress caused by intracellular 2-aminoacrylate accumulation leads to pleiotropic growth defects in a variety of organisms. Members of the well-conserved RidA/YER057c/UK114 protein family prevent enamine stress by enhancing the breakdown of 2-aminoacrylate to pyruvate. In Salmonella enterica, disruption of RidA allows 2-aminoacrylate to accumulate and to inactivate a variety of pyridoxal 5'-phosphate-dependent enzymes by generating covalent bonds with the enzyme and/or cofactor. This study was initiated to identify mechanisms that can overcome 2-aminoacrylate stress in the absence of RidA. Multicopy suppressor analysis revealed that overproduction of the methionine biosynthesis enzyme cystathionine β-lyase (MetC) (EC 4.4.1.8) alleviated the pleiotropic consequences of 2-aminoacrylate stress in a ridA mutant strain. Degradation of cystathionine by MetC was not required for suppression of ridA phenotypes. The data support a model in which MetC acts on a noncystathionine substrate to generate a metabolite that reduces 2-aminoacrylate levels, representing a nonenzymatic mechanism of 2-aminoacrylate depletion.IMPORTANCE RidA proteins are broadly conserved and have been demonstrated to deaminate 2-aminoacrylate and other enamines. 2-Aminoacrylate is generated as an obligatory intermediate in several pyridoxal 5'-phosphate-dependent reactions; if it accumulates, it damages cellular enzymes. This study identified a novel mechanism to eliminate 2-aminoacrylate stress that required the overproduction, but not the canonical activity, of cystathionine β-lyase. The data suggest that a metabolite-metabolite interaction is responsible for quenching 2-aminoacrylate, and they emphasize the need for emerging technologies to probe metabolism in vivo.