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The RidA (YjgF/YER057c/UK114) family of proteins is broadly conserved in the three domains of life yet the functional understanding of these proteins is at an early stage. Physiological studies of ridA mutant strains of Salmonella enterica provided a framework to inform in vitro studies and led to the description of a conserved biochemical activity for this family. ridA mutant strains of S. enterica have characteristic phenotypes including new synthesis of thiamine biosynthetic intermediate phosphoribosylamine (PRA), inability to grow on pyruvate as a sole carbon and energy source or when serine is present in the minimal growth medium, and a decreased specific activity of transaminase B (IlvE). Secondary mutations restoring growth to a ridA mutant in the presence of serine were in dapA (encoding dihydrodipicolinate synthase) and thrA (encoding homoserine dehydrogenase). These mutations suppressed multiple ridA mutant phenotypes by increasing the synthesis of threonine. The ability of threonine to suppress the metabolic defects of a ridA mutant is discussed in the context of recent biochemical data and in vivo results presented here. [ABSTRACT FROM AUTHOR]

The periplasmic protein ApbE was identified through the analysis of several mutants defective in thiamine biosynthesis and was implicated as having a role in iron-sulfur cluster biosynthesis or repair. While mutations in apbE cause decreased activity of several iron-sulfur enzymes in vivo, the specific role of ApbE remains unknown. Members of the AbpE family include NosX and RnfF, which have been implicated in oxidation-reduction associated with nitrous oxide and nitrogen metabolism, respectively. In this work, we show that ApbE binds one FAD molecule per monomeric unit. The structure of ApbE in the presence of bound FAD reveals a new FAD-binding motif. Protein variants that are nonfunctional in vivo were generated by random and targeted mutagenesis. Each variant was substituted in the environment of the FAD and analyzed for FAD binding after reconstitution. The variant that altered a key tyrosine residue involved in FAD binding prevented reconstitution of the protein. [ABSTRACT FROM AUTHOR]