Abstract
Prenylated proteins contain either a 15-carbon farnesyl or a 20-carbon geranylgeranyl isoprenoid covalently attached via a thioether bond to a cysteine residue at or near their C terminus. As prenylated proteins comprise up to 2% of the total protein in eukaryotic cells, and the thioether bond is a stable modification, their degradation raises a metabolic challenge to cells. A lysosomal enzyme termed prenylcysteine lyase has been identified that cleaves prenylcysteines to cysteine and an unidentified isoprenoid product. Here we show that the isoprenoid product of prenylcysteine lyase is the C-1 aldehyde of the isoprenoid moiety (farnesal in the case of C-15). The enzyme requires molecular oxygen as a cosubstrate and utilizes a noncovalently bound flavin cofactor in an NAD(P)H-independent manner. Additionally, a stoichiometric amount of hydrogen peroxide is produced during the reaction. These surprising findings indicate that prenylcysteine lyase utilizes a novel oxidative mechanism to cleave thioether bonds and provide insight into the unique role this enzyme plays in the cellular metabolism of prenylcysteines.
Highlights
From the Departments of ‡Pharmacology and Cancer Biology and ʈBiochemistry, Duke University Medical Center, Durham, North Carolina 27710 and the ¶Department of Chemistry, University of Illinois, Urbana, Illinois 61801
Prenylated proteins contain either a 15-carbon farnesyl or a 20-carbon geranylgeranyl isoprenoid covalently attached via a thioether bond to a cysteine residue at or near their C terminus
A stoichiometric amount of hydrogen peroxide is produced during the reaction. These surprising findings indicate that prenylcysteine lyase utilizes a novel oxidative mechanism to cleave thioether bonds and provide insight into the unique role this enzyme plays in the cellular metabolism of prenylcysteines
Summary
A stoichiometric amount of hydrogen peroxide is produced during the reaction These surprising findings indicate that prenylcysteine lyase utilizes a novel oxidative mechanism to cleave thioether bonds and provide insight into the unique role this enzyme plays in the cellular metabolism of prenylcysteines. One major class of lipid modification is termed prenylation, in which either a 15-carbon farnesyl or 20-carbon geranylgeranyl isoprenoid is covalently attached via a thioether bond to cysteine residue(s) at or near the C terminus of the protein [2, 3]. In a continuing effort to understand the metabolic fate of prenylcysteines produced during turnover of prenylated proteins, we identified and cloned a lysosomal enzyme that catalyzes the degradation of prenylcysteines [10, 11] This enzyme, dubbed prenylcysteine lyase (PCLase), degrades prenylcysteines to yield free cysteine and an unidentified isoprenoid product [10]. The unusual mechanism of the reaction catalyzed by PCLase was investigated
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