Publication Date
8-21-2020
Journal
Journal of Molecular Biology
DOI
10.1016/j.jmb.2020.05.017
PMID
32470559
PMCID
PMC7483794
PubMedCentral® Posted Date
8-21-2021
PubMedCentral® Full Text Version
Author MSS
Published Open-Access
yes
Keywords
Animals, Catalytic Domain, Crystallography, X-Ray, Cytochrome-B(5) Reductase, Cytochromes b5, HEK293 Cells, Humans, Iron, Mice, Models, Molecular, Protein Conformation, Protein Domains, Sf9 Cells, Stearoyl-CoA Desaturase, Zinc, SCD1, membrane enzyme, diiron center, electron transfer, double bond formation
Abstract
Stearoyl-CoA desaturase 1 (SCD1) is a membrane-embedded metalloenzyme that catalyzes formation of a double-bond on a saturated acyl-CoA. SCD1 has a diiron center and its proper function requires an electron transport chain composed of NADH (or NADPH), cytochrome b5 reductase (b5R), and cytochrome b5 (cyt b5). Since SCD1 is a key regulator in fat metabolism and is required for survival of cancer cells, there is intense interest in targeting SCD1 for various metabolic diseases and cancers. Crystal structures of human and mouse SCD1 were reported recently, however, both proteins have two zinc ions instead of two iron ions in the catalytic center and as a result, the enzymes are inactive. Here we report a general approach for incorporating iron into heterologously expressed proteins in HEK293 cells. We produced mouse SCD1 that contains a diiron center, and visualized its diiron center by solving its crystal structure to 3.5 Å. We assembled the entire electron transport chain using the purified soluble domains of cyt b5 and b5R, and the purified mouse SCD1, and we showed that three proteins coordinate to produce proper products. These results established an in vitro system that allows precise perturbations of the electron transport chain for the understanding of the catalytic mechanism in SCD1.
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