Fatty Acids Bind to the StAR‐Related Lipid Transfer Domain of Thioesterase Superfamily Member 1, a Master Regulator of Thermogenesis and Energy Expenditure
Authors: Tillman Matt C. , Ortlund Eric 
Published: June 2021

Obesity and other metabolic diseases have become a global epidemic, greatly increasing in prevalence over the past 30 years. In mammals, brown adipose tissue counteracts obesity through a process called thermogenesis, which is the process of burning fat to produce heat in order to maintain body temperature. Thioesterase superfamily member 1 (Them1) was recently discovered as a protein highly expressed in brown adipose tissue that negatively regulates thermogenesis and is linked to obesity. Them1 is a multi‐domain enzyme that plays an important role in slowing lipid metabolism through converting acyl‐CoA into free fatty acids, thus preventing acyl‐CoA from being used in lipid metabolism. In addition to Them1's enzymatic domains, it also contains a lipid‐binding StAR‐related lipid transfer (START) domain with an unknown function. It was previously shown that the START domain is necessary for the full enzymatic activity of the protein, suggesting the START domain does interact with the enzymatic domains. We hypothesized that the lipid‐binding START domain regulates the activity of the enzymatic domains, serving as a lipid sensor in the cell to control lipid metabolism. In order to test this hypothesis, we identified that the START domain binds to long chained fatty acids, such as myristic acid (14:0) and oleic acid (18:1), using mass spectrometry. We then solved the crystal structure of the START domain bound and unbound to myristic acid to determine how lipid binding alters the conformation of Them1. There were no observable differences between the two structures; therefore, we tested if lipid binding altered the stability of the protein using a thermal shift assay. Myristic acid and oleic acid stabilized the protein, suggesting that despite there being no observable differences between the two crystal structures, lipid binding does likely alter the dynamics of the protein. To further investigate this, we created a full‐length model of Them1 by joining together the crystal structure of the START domain and a homologous proteins' enzymatic domains. Using molecular dynamics with this model, we detected myristic acid altered the communication within the START domain, but not in the enzymatic domains. Lastly, we observed that the enzymatic activity of Them1 was not significantly altered in the presence of different fatty acids that bind to the START domain, all of which suggests that lipid binding to the START domain doesn't directly regulate the enzymatic activity of Them1. In conclusion, we have identified what binds to the START domain of Them1 and determined the first structure of the START domain bound to myristic acid. Our current data suggests that lipid binding to the START domain doesn't directly regulate the enzymatic activity of Them1. However, we are now equipped to use our structure to develop mutant forms of Them1 that can't bind to fatty acids, which can be used to further understand the role of lipid binding to the START domain.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.