NYMC Faculty Publications

Cystine Rather Than Cysteine Is the Preferred Substrate for Β-Elimination by Cystathionine Γ-Lyase: Implications for Dietary Methionine Restriction

Author Type(s)

Faculty

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Research Article with Highest Number of Citations for NYMC First Author (Scopus)

DOI

10.1007/s11357-023-00788-4

Journal Title

Geroscience

First Page

3617

Last Page

3634

Document Type

Article

Publication Date

8-1-2024

Department

Biochemistry and Molecular Biology

Keywords

Cystathionine beta-synthase, Cystathionine gamma-lyase, Cysteine, Cystine, Methionine restriction, Transsulfuration

Disciplines

Medicine and Health Sciences

Abstract

Dietary methionine restriction (MR) increases longevity by improving health. In experimental models, MR is accompanied by decreased cystathionine β-synthase activity and increased cystathionine γ-lyase activity. These enzymes are parts of the transsulfuration pathway which produces cysteine and 2-oxobutanoate. Thus, the decrease in cystathionine β-synthase activity is likely to account for the loss of tissue cysteine observed in MR animals. Despite this decrease in cysteine levels, these tissues exhibit increased H2S production which is thought to be generated by β-elimination of the thiol moiety of cysteine, as catalyzed by cystathionine β-synthase or cystathionine γ-lyase. Another possibility for this H2S production is the cystathionine γ-lyase-catalyzed β-elimination of cysteine persulfide from cystine, which upon reduction yields H2S and cysteine. Here, we demonstrate that MR increases cystathionine γ-lyase production and activities in the liver and kidneys, and that cystine is a superior substrate for cystathionine γ-lyase catalyzed β-elimination as compared to cysteine. Moreover, cystine and cystathionine exhibit comparable Kcat/Km values (6000 M−1 s−1) as substrates for cystathionine γ-lyase-catalyzed β-elimination. By contrast, cysteine inhibits cystathionine γ-lyase in a non-competitive manner (Ki ~ 0.5 mM), which limits its ability to function as a substrate for β-elimination by this enzyme. Cysteine inhibits the enzyme by reacting with its pyridoxal 5′-phosphate cofactor to form a thiazolidine and in so doing prevents further catalysis. These enzymological observations are consistent with the notion that during MR cystathionine γ-lyase is repurposed to catabolize cystine and thereby form cysteine persulfide, which upon reduction produces cysteine.

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