Department of Chemistry , The University of British Columbia , Okanagan Campus, 3247 University Way , Kelowna , BC V1V 1V7 , Canada.
Biochemistry. 2019 Aug 27;58(34):3592-3603. doi: 10.1021/acs.biochem.9b00487. Epub 2019 Aug 13.
is a common oral bacterium and a major producer of HS, a toxic gas linked to the pathogenesis of periodontal disease. The bacterium encodes a fold type II pyridoxal l-phosphate (PLP)-dependent enzyme, Fn1220 or lanthionine synthase (LS), that generates HS and l-lanthionine (a component of the peptidoglycan layer) through β-replacement of l-cysteine by a second molecule of l-cysteine. Herein, we show through detailed kinetic analysis that LS elicits catalytic promiscuity as demonstrated for other fold type II PLP-dependent homologues, namely, -acetylserine sulfhydrylase (OASS) and cystathionine β-synthase (CBS). Like OASS, LS can assimilate HS by catalyzing the β-replacement of -acetyl-l-serine by sulfide to form l-cysteine. However, the turnover for this reaction in LS is slower than that of other studied OASS enzymes due to slower conversion to the α-aminoacrylate intermediate. Similar to yeast and human CBS, LS can generate HS and l-cystathionine through β-replacement of l-cysteine by a second molecule of l-homocysteine; however, whereas this is the main HS-forming reaction in CBS, it is not for LS. LS shows a marked preference for forming HS and l-lanthionine through the condensation of 2 equiv of l-cysteine. Sequence alignment of LS with other CBS and OASS enzymes and inspection of the LS crystal structure in the external aldimine state with l-lanthionine reveal that LS possesses a unique loop that engages in hydrogen-bond contact with the product, providing a structural rationale for the enzyme's catalytic preference for HS and l-lanthionine biosynthesis.
牙龈卟啉单胞菌是一种常见的口腔细菌，也是 HS 的主要产生者，HS 是一种与牙周病发病机制有关的有毒气体。该细菌编码一种折叠类型 II 吡哆醛 l-磷酸（PLP）依赖性酶，Fn1220 或 lanthionine 合酶（LS），通过第二个 l-半胱氨酸分子的β取代生成 HS 和 l-高丝氨酸（肽聚糖层的一个组成部分）。在此，我们通过详细的动力学分析表明，LS 表现出催化混杂性，就像其他折叠类型 II PLP 依赖性同系物一样，即 -乙酰丝氨酸硫醇酶（OASS）和胱硫醚 β-合酶（CBS）。与 OASS 一样，LS 可以通过催化 -乙酰-l-丝氨酸与硫化物的β取代来同化 HS，形成 l-半胱氨酸。然而，由于转化为 α-氨基丙烯酸中间体较慢，该反应在 LS 中的周转率比其他研究的 OASS 酶慢。与酵母和人 CBS 相似，LS 可以通过第二个 l-高半胱氨酸分子的β取代生成 HS 和 l-胱硫醚；然而，尽管这是 CBS 中主要的 HS 形成反应，但对于 LS 则不是。LS 表现出明显的偏爱，通过 2 当量的 l-半胱氨酸缩合形成 HS 和 l-高丝氨酸。LS 与其他 CBS 和 OASS 酶的序列比对以及 LS 晶体结构在外部亚胺态与 l-高丝氨酸的检查表明，LS 具有独特的环，与产物形成氢键接触，为酶对 HS 和 l-高丝氨酸生物合成的催化偏好提供了结构基础。
