In histidine and tryptophan biosynthesis, two related isomerization reactions are generally catalyzed by two specific single-substrate enzymes (HisA and TrpF), sharing a similar (
β
/
α
)
8
-barrel scaffold. However, in some actinobacteria, one of the two encoding genes (
trpF
) is missing and the two reactions are instead catalyzed by one bisubstrate enzyme (PriA). To unravel the unknown mechanism of bisubstrate specificity, we used the
Mycobacterium tuberculosis
PriA enzyme as a model. Comparative structural analysis of the active site of the enzyme showed that PriA undergoes a reaction-specific and substrate-induced metamorphosis of the active site architecture, demonstrating its unique ability to essentially form two different substrate-specific actives sites. Furthermore, we found that one of the two catalytic residues in PriA, which are identical in both isomerization reactions, is recruited by a substrate-dependent mechanism into the active site to allow its involvement in catalysis. Comparison of the structural data from PriA with one of the two single-substrate enzymes (TrpF) revealed substantial differences in the active site architecture, suggesting independent evolution. To support these observations, we identified six small molecule compounds that inhibited both PriA-catalyzed isomerization reactions but had no effect on TrpF activity. Our data demonstrate an opportunity for organism-specific inhibition of enzymatic catalysis by taking advantage of the distinct ability for bisubstrate catalysis in the
M. tuberculosis
enzyme.
在组氨酸和色氨酸生物合成中,通常由两种特定的单底物酶(HisA和TrpF)催化两个相关的异构化反应,共享相似的(β/α)8-桶状结构。然而,在一些放线菌中,其中一种编码基因(trpF)缺失,这两个反应被一种双底物酶(PriA)代替催化。为了揭示双底物特异性的未知机制,我们使用结核分枝杆菌PriA酶作为模型。对酶的活性位点进行比较结构分析表明,PriA经历了一个反应特异性和底物诱导的活性位点结构变化,展示了其独特的能力,基本上形成了两个不同的底物特异性活性位点。此外,我们发现PriA中的两个催化残基之一,在两个异构化反应中是相同的,通过底物依赖机制被招募到活性位点中,以允许其参与催化。将PriA的结构数据与两种单底物酶之一(TrpF)进行比较,发现活性位点结构存在显著差异,表明它们是独立进化的。为了支持这些观察结果,我们确定了六种小分子化合物,能够抑制PriA催化的两个异构化反应,但对TrpF的活性没有影响。我们的数据表明,通过利用结核分枝杆菌酶的双底物催化的独特能力,可以实现有机体特异性的酶催化抑制。