Binding site of cerulenin in fatty acid synthetase

An antibiotic cerulenin, (2R, 3S)-2,3-epoxy-4-oxo-7,10-trans,trans- dodecadienamide, irreversibly inhibits fatty acid synthetase from Saccharomyces cerevisiae. Three moles of cerulenin were bound to 1 mol of the enzyme with concomitant loss of its activity. Pretreatment of the enzyme with iodoacetamide reduced the amount of cerulenin bound to the enzyme. Since iodoacetamide is known to specifically bind to the cysteine residue on the condensing reaction domain, cerulenin is considered to bind to the same domain. Tryptic digestion of the [3H] cerulenin-treated enzyme gave a radioactive peptide; its amino acid composition was Asx 1, Thr 1, Ser 1, Glx 2, Pro 1, Gly 1, Ala 1, Val 1, Ile 1, and Leu 2. This composition included all the amino acids of the condensing reaction site (Thr-Pro-Val-Gly-Ala-Cys) previously reported by Kresze et al. (Eur. J. Biochem., 79, 181 [1977] except for Cys. When the enzyme was treated with [3H]cerulenin and digested successively with trypsin and carboxypeptidase P, a [3H] cerulenin-cysteine adduct was isolated as the sole product. This was identified with the adduct chemically synthesized from non-labeled cerulenin and cysteine, and its structure was elucidated by 1H-, 13C-NMR, and fast atom bombardment mass spectrometry. These results indicate that cerulenin, forming a hydroxylactam ring, reacts at its epoxide carbon (C-2 position) with the SH-group of the cysteine residue in the condensing reaction domain of yeast fatty acid synthetase.