Crystal structure of FAS thioesterase domain with polyunsaturated fatty acyl adduct and inhibition by dihomo-γ-linolenic acid

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 108; no. 38; pp. 15757 - 15762
• Main Authors: Zhang, Wei, Chakravarty, Bornali, Zheng, Fei, Gu, Ziwei, Wu, Hongmei, Mao, Jianqiang, Wakil, Salih J, Quiocho, Florante A
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 20.09.2011; National Acad Sciences
• Subjects: 3T3-L1 Cells; 8,11,14-Eicosatrienoic Acid - pharmacology; Active sites; Adipocytes - drug effects; Adipocytes - metabolism; alpha-linolenic acid; alpha-Linolenic Acid - pharmacology; Animals; Biocatalysis - drug effects; Biological Sciences; Biosynthesis; Breast cancer; breast neoplasms; Cancer; Catalytic Domain; Cell Line, Tumor; Cell lines; Crystal structure; Crystallization; Crystallography, X-Ray; diabetes; Esters; Fatty Acid Synthases - chemistry; Fatty Acid Synthases - metabolism; Fatty acids; Fatty Acids - biosynthesis; Fatty Acids, Unsaturated - chemistry; Fatty Acids, Unsaturated - metabolism; fatty-acid synthase; heart diseases; Humans; hydrolysis; long chain polyunsaturated fatty acids; Mice; Models, Molecular; Molecular Structure; Palmitates; phosphorylation; Protein Binding - drug effects; Protein Structure, Tertiary; serine; therapeutics; Thiolester Hydrolases - chemistry; Thiolester Hydrolases - metabolism; Unsaturated fatty acids
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1112334108

Human fatty acid synthase (hFAS) is a homodimeric multidomain enzyme that catalyzes a series of reactions leading to the de novo biosynthesis of long-chain fatty acids, mainly palmitate. The carboxy-terminal thioesterase (TE) domain determines the length of the fatty acyl chain and its ultimate release by hydrolysis. Because of the upregulation of hFAS in a variety of cancers, it is a target for antiproliferative agent development. Dietary long-chain polyunsaturated fatty acids (PUFAs) have been known to confer beneficial effects on many diseases and health conditions, including cancers, inflammations, diabetes, and heart diseases, but the precise molecular mechanisms involved have not been elucidated. We report the Formula crystal structure of the hFAS TE domain covalently modified and inactivated by methyl γ-linolenylfluorophosphonate. Whereas the structure confirmed the phosphorylation by the phosphonate head group of the active site serine, it also unexpectedly revealed the binding of the 18-carbon polyunsaturated γ-linolenyl tail in a long groove-tunnel site, which itself is formed mainly by the emergence of an α helix (the "helix flap"). We then found inhibition of the TE domain activity by the PUFA dihomo-γ-linolenic acid; γ- and α-linolenic acids, two popular dietary PUFAs, were less effective. Dihomo-γ-linolenic acid also inhibited fatty acid biosynthesis in 3T3-L1 preadipocytes and selective human breast cancer cell lines, including SKBR3 and MDAMB231. In addition to revealing a novel mechanism for the molecular recognition of a polyunsaturated fatty acyl chain, our results offer a new framework for developing potent FAS inhibitors as therapeutics against cancers and other diseases.