Figure 1.
The biosynthetic pathways for thiamine and histidine in S. enterica.
Panel A shows relevant steps from the thiamine biosynthetic pathway while panel B shows relevant steps in the histidine synthetic pathway, both in S. enterica. The enzymatic steps that lead to the formation of their respective end products are show. Abbreviations: Gln, glutamine; PRPP, phosphoribosyl pyrophosphate; PRA, phosphoribosylamine; Gly, glycine; GAR, glycineamide ribonucleotide; ProFAR, 1-(5-phosphoribosyl)-5-[(5-phosphoribosylamino)methylideneamino]imidazole-4-carboxamide; PRFAR, 5-[(5-Phospho-1-deoxyribulos-1-ylamino)methylideneamino]-1-(5-phosphoribosyl)imidazole-4-carboxamide.
Table 1.
Bacterial strains.
Table 2.
Diverse mutations in hisA allow PurF-independent PRA synthesis.
Figure 2.
Growth analysis of hisA mutant strain.
Growth curves were performed by monitoring optical density (OD) at 650 nm. Shown is a purF2085 gnd174::MudJ hisA1451 (DM10350) strain grown in minimal glucose adenine medium (open triangle), with thiamine (open square), with histidine (filled triangle), and with histidine and thiamine (filled square).
Table 3.
Growth rates of some hisA mutant strains are increased by exogenous histidine.
Table 4.
Metabolic flux to ProFAR is required for PurF-independent PRA synthesis.
Figure 3.
HPLC separation of ProFAR breakdown products.
The dashed line indicates the trace of stock 1 mM ProFAR used for this assay. The solid line (offset) indicates the trace of 1 mM ProFAR pH 7.5 after incubation at 37°C for 26 hours. Stars indicate unknown break down products. Abbreviations: AICAR, 5-amino-4-imidazolecarboxamide ribonucleotide; ProFAR, 1-(5-phosphoribosyl)-5-[(5-phosphoribosylamino)methylideneamino]imidazole-4-carboxamide.
Figure 4.
Possible mechanisms for PRA formation from ProFAR.
General mechanisms for PRA formation from ProFAR are depicted schematically. In pathway I, ProFAR is hydrolyzed to generate R5P by a mechanism that likely requires an enzyme. Ammonia is also released from the non-R5P product and is then available for non-enzymatic formation of PRA. It is possible the R5P and/or the ammonia do not leave the active site of the relevant enzyme. Pathway II depicts the formation of PRA as a direct product and implicates an undefined enzyme-catalyzed mechanism. Abbreviations: ProFAR, 1-(5-phosphoribosyl)-5-[(5-phosphoribosylamino) methylideneamino] imidazole-4-carboxamide; R5P, ribose-5′-phosphate; PRA, phosphoribosylamine.