Structural and Kinetic Insight into the Biosynthesis of H2S and L-Lanthionine from L-Cysteine by a Pyridoxal L-Phosphate-Dependent Enzyme from Fusobacterium nucleatum
Structural and Kinetic Insight into the Biosynthesis of H2S and L-Lanthionine from L-Cysteine by a Pyridoxal L-Phosphate-Dependent Enzyme from Fusobacterium nucleatum
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DOI：
10.1021/acs.biochem.9b00487
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发表时间：
2019-08-27
期刊：
影响因子：
2.9
通讯作者：
Wolthers, Kirsten R.
中科院分区：
文献类型：
--
作者：
Mothersole, Robert G.;Wolthers, Kirsten R.
Fusobacterium nucleatum is a common oral bacterium and a major producer of H2S, 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 H2S and L-lanthionine (a component of the peptidoglycan layer) through beta-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, O-acetylserine sulfhydrylase (OASS) and cystathionine beta-synthase (CBS). Like OASS, LS can assimilate H2S by catalyzing the beta-replacement of O-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 alpha-aminoacrylate intermediate. Similar to yeast and human CBS, LS can generate H2S and L-cystathionine through beta-replacement of L-cysteine by a second molecule of L-homocysteine; however, whereas this is the main H2S-forming reaction in CBS, it is not for LS. LS shows a marked preference for forming H2S 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 H2S and L-lanthionine biosynthesis.
