Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX 77843-2128, United States.
Natural Products LINCHPIN Laboratory, Texas A&M University, 3255 TAMU, College Station, TX 77840, United States.
Biochem Biophys Res Commun. 2014 Jul 18;450(1):679-84. doi: 10.1016/j.bbrc.2014.06.034. Epub 2014 Jun 14.
Catalytic promiscuity, which is the ability to catalyze more than one reaction in the same active site, is thought to facilitate the evolution of new protein functions. Although many enzymes are catalytically promiscuous, there is little direct evidence to show how promiscuous activities evolved into biological functions. We are seeking evidence for this model by studying the o-succinylbenzoate synthase (OSBS) family. Most enzymes within this family only catalyze OSBS, which is a step in menaquinone synthesis. However, several characterized enzymes in one branch of the family (called the NSAR/OSBS subfamily) efficiently catalyze both OSBS and N-succinylamino acid racemization (NSAR). Based on genome context, NSAR appears to be the only biological function of some characterized NSAR/OSBS enzymes, while both activities are biologically relevant in others. The promiscuity model predicts that these enzymes evolved from an ancestral OSBS which promiscuously catalyzed NSAR as a side reaction that was not biologically relevant. If so, the model predicts that some extant OSBS enzymes would have low levels of promiscuous NSAR activity. This manuscript describes such an enzyme from Exiguobacterium sp. AT1b (ExiOSBS). We show that ExiOSBS efficiently catalyzes OSBS (kcat/KM=2.6×10(6) M(-1) s(-1)), but its efficiency for the NSAR reaction is only 41 M(-1) s(-1). Moreover, genome context indicates that OSBS is the only biologically relevant activity. ExiOSBS diverged from the NSAR/OSBS subfamily before NSAR emerged as a biologically relevant activity. These results provide evidence that NSAR activity originated as a promiscuous activity in an ancestor of the NSAR/OSBS subfamily.
催化多功能性，即在同一活性部位催化不止一种反应的能力，被认为有助于新蛋白质功能的进化。尽管许多酶具有催化多功能性，但很少有直接的证据表明多功能活性是如何演变成生物功能的。我们通过研究邻琥珀酰苯甲酸合酶（OSBS）家族来寻找这一模型的证据。该家族中的大多数酶仅催化 OSBS，这是甲萘醌合成的一个步骤。然而，该家族的一个分支（称为 NSAR/OSBS 亚科）中的几个特征酶有效地催化 OSBS 和 N-琥珀酰氨基酸外消旋化（NSAR）。根据基因组背景，NSAR 似乎是一些特征 NSAR/OSBS 酶的唯一生物学功能，而在其他酶中，两种活性都是生物学相关的。多功能性模型预测，这些酶是从一个原始的 OSBS 进化而来的，该酶最初是作为一个不重要的副反应而具有多功能性地催化 NSAR。如果是这样，该模型预测某些现存的 OSBS 酶将具有较低水平的多功能 NSAR 活性。本文描述了来自极端嗜热杆菌 AT1b（Exiguobacterium sp. AT1b）的这种酶（ExiOSBS）。我们表明，ExiOSBS 有效地催化 OSBS（kcat/KM=2.6×10(6) M(-1) s(-1)），但其 NSAR 反应的效率仅为 41 M(-1) s(-1)。此外，基因组背景表明 OSBS 是唯一具有生物学相关性的活性。ExiOSBS 在 NSAR 作为一种具有生物学相关性的活性出现之前，就已经从 NSAR/OSBS 亚科中分化出来。这些结果提供了证据，证明 NSAR 活性起源于 NSAR/OSBS 亚科祖先的一种多功能活性。
