H2S Biogenesis by Human Cystathionine γ-Lyase Leads to the Novel Sulfur Metabolites Lanthionine and Homolanthionine and Is Responsive to the Grade of Hyperhomocysteinemia

Abstract

Although there is a growing recognition of the significance of hydrogen sulfide (H 2 S) as a biological signaling molecule involved in vascular and nervous system functions, its biogenesis and regulation are poorly understood. It is widely assumed that desulfhydration of cysteine is the major source of H 2 S in mammals and is catalyzed by the transsulfuration pathway enzymes, cystathionine ␤-synthase and cystathionine ␥-lyase (CSE). In this study, we demonstrate that the profligacy of human CSE results in a variety of reactions that generate H 2 S from cysteine and homocysteine. The ␥-replacement reaction, which condenses two molecules of homocysteine, yields H 2 S and a novel biomarker, homolanthionine, which has been reported in urine of homocystinuric patients, whereas a ␤-replacement reaction, which condenses two molecules of cysteine, generates lanthionine. Kinetic simulations at physiologically relevant concentrations of cysteine and homocysteine, reveal that the ␣,␤-elimination of cysteine accounts for ϳ70% of H 2 S generation. However, the relative importance of homocysteinederived H 2 S increases progressively with the grade of hyperhomocysteinemia, and under conditions of severely elevated homocysteine (200 M), the ␣,␥-elimination and ␥-replacement reactions of homocysteine together are predicted to account for ϳ90% of H 2 S generation by CSE. Excessive H 2 S production in hyperhomocysteinemia may contribute to the associated cardiovascular pathology.H 2 S is the newest member of a growing list of gaseous signaling molecules that modulate physiological functions (1-3). Concentrations of H 2 S ranging from 50 to 160 M have been reported in the brain (4), where it appears to function as a neuromodulator by potentiating the activity of the N-methyl-Daspartate receptor and by altering induction of long term potentiation in the hippocampus, important for memory and learning (5). H 2 S levels in human plasma are reported to be ϳ50 M, and in vitro studies suggest that it functions as a vasodilator by opening K ATP channels in vascular smooth muscle cells (6).A recent in vivo study has demonstrated the efficacy of H 2 S in attenuating myocardial ischemia-reperfusion injury by protecting mitochondrial function (7). The role of H 2 S in inflammation is suggested by several studies (8 -11); however, the underlying mechanism is unknown. Remarkably, H 2 S can also induce a state of suspended animation in mice by decreasing the metabolic rate and the core body temperature presumably by inhibiting cytochrome c oxidase in the respiratory chain (12).Endogenous H 2 S is presumed to be generated primarily by desulfhydration of cysteine catalyzed by the two pyridoxal phosphate (PLP) 3 -dependent enzymes in the transsulfuration pathway: cystathionine ␤-synthase (CBS) and cystathionine ␥-lyase (CSE) (13,14). In fact, it is widely assumed, based on the reported absences of CSE in the brain (15) and of H 2 S in the brain of CBS knock-out mice (16), that CBS is the primary source of H 2 S in this organ, whereas CSE plays the...

Increased transsulfuration mediates longevity and dietary restriction in Drosophila

“…We find that DR increases dCBS protein more than it does enzyme activity, suggesting that components of the TSP, along with metabolites involved in one-carbon metabolism, might be regulated posttranslationally through modification by sumoylation or allosteric regulation by AdoMet (10,34). Furthermore, the TSP is the primary source of hydrogen sulfide production in the cell (35)(36)(37). Recent years have seen the identification of H 2 S as an important gaseous signaling molecule with physiological roles in nervous, vascular, and intestinal systems (38)(39)(40).…”

Redox Biochemistry of Hydrogen Sulfide

“…The relaxed substrate specificity of CBS and CSE combined with the catalytic versatility of CSE to act at both the ␤-carbons and the ␥-carbons of substrates results in multiple H 2 S-generating reactions (Fig. 1a) (13,14). Extensive kinetic characterization of these reactions at a physiologically relevant pH have led to the following conclusions.…”

Selective fluorescent probes for live-cell monitoring of sulphide

“…The amino acid cysteine and glutathione (reduced) (GSH) can both serve as potential sulphide sources. The previously mentioned enzymes, CBS and cystathionine γ-lyase, both use cysteine as a substrate for H 2 S production 8,9,[18][19][20] . GSH can be broken down by γ-glutayml transpeptidase and a dipeptidase to give cysteine [21][22][23] , which can then be converted to H 2 S. Therefore, we tested whether a perturbation of the intracellular levels of either cysteine, or GSH could result in an increased cellular concentration of H 2 S. Imaging experiments were carried out with SFP-2, as previously described, and cells were incubated with either 100 µM GSH or cysteine.…”

“…H 2 S, or aqueous sulphide, elicits diverse physiological responses, including modulation of blood pressure and reduction of ischemia reperfusion injury [3][4][5] , exertion of anti-inflammatory effects 6 and reduction of metabolic rate 7 . The production of H 2 S is catalysed by the two pyridoxal 5′-phosphate-dependent enzymes, cystathionine β-synthase (CBS) 8 , and cystathionine γ-lyase 9 , and indirectly, via a pyridoxal 5′-phosphateindependent enzyme, 3-mercaptopyruvate sulphurtransferase 10 .…”