Allosteric regulation of thioesterase superfamily member 1 by lipid sensor domain binding fatty acids and lysophosphatidylcholine

Abstract

Nonshivering thermogenesis occurs in brown adipose tissue to generate heat in response to cold ambient temperatures. Thioesterase superfamily member 1 (Them1) is transcriptionally up-regulated in brown adipose tissue upon exposure to the cold and suppresses thermogenesis in order to conserve energy reserves. It hydrolyzes long-chain fatty acyl-CoAs that are derived from lipid droplets, preventing their use as fuel for thermogenesis. In addition to its enzymatic domains, Them1 contains a C-terminal StAR-related lipid transfer (START) domain with unknown ligand or function. By complementary biophysical approaches, we show that the START domain binds to long-chain fatty acids, products of Them1’s enzymatic reaction, as well as lysophosphatidylcholine (LPC), lipids shown to activate thermogenesis in brown adipocytes. Certain fatty acids stabilize the START domain and allosterically enhance Them1 catalysis of acyl-CoA, whereas 18:1 LPC destabilizes and inhibits activity, which we verify in cell culture. Additionally, we demonstrate that the START domain functions to localize Them1 near lipid droplets. These findings define the role of the START domain as a lipid sensor that allosterically regulates Them1 activity and spatially localizes it in proximity to the lipid droplet.

Identifying Cancer-Relevant Mutations in the DLC START Domain Using Evolutionary and Structure-Function Analyses

“…The remaining overrepresented COSMIC missense mutations may similarly impact START activity or affect other properties, such as ligand binding or conformational change. A potential DLC START regulatory mechanism is suggested by studies of both minimal and multidomain START-containing proteins, demonstrating that START domains can stimulate regulatory outputs in an allosteric manner [32,35]. If the DLC START domain functions similarly, it could promote RhoGAP tumor suppressor activity, possibly via allosteric regulation of intra-or inter-molecular interactions.…”

“…The DLC-2 START cavity contains more polar side chains than the cavities of cholesterol-binding START domains, and DLC START domains were therefore proposed to bind fatty acid, rather than sterol, ligands [43]. Supporting this, the STARD14 START domain, which shares characteristics of the DLC START binding pocket, was recently shown to bind several species of fatty acids [32]. Taken together, our data identify several conserved residues likely to underlie the START-directed regulation of DLC-1 and DLC-2 tumor-suppressive capabilities.…”

“…Structurally, these proteins can be divided into two classes: minimal START proteins and multidomain STARTcontaining proteins which possess a wide variety of additional functional domains [31]. START domains employ a range of complex regulatory mechanisms [19,20,[32][33][34]. Of particular interest, START domains in both minimal and multidomain START-containing proteins are able to stimulate regulatory outputs of interacting partners or co-occurring domains in a ligand-dependent manner Rho GTPases have a globular structure with a limited druggable surface, making them particularly challenging drug targets [5][6][7].…”

“…START domains employ a range of complex regulatory mechanisms [19,20,[32][33][34]. Of particular interest, START domains in both minimal and multidomain START-containing proteins are able to stimulate regulatory outputs of interacting partners or co-occurring domains in a ligand-dependent manner [32,35]. In the context of DLC proteins, this would be predicted to manifest as START-dependent promotive effects on tumor suppressor activity.…”

Evolutionary Analysis of the Steroidogenic Acute Regulatory Protein-Related Lipid Transfer Domain and Its Response to Salt Stress In Vitis Vinifera

“…The steroidogenic acute regulatory protein-related lipid transfer (START) domain, which was rst discovered in mammals, has a 210-amino-acid conserved sequence, which forms an α/β helix-grip structure, thereby creating a hydrophobic cavity that binds to the ligand and small globular modules (Roderick et al 2002;Schrck et al 2004;Clark 2012Clark , 2020Tillman et al 2020). Evidence shows that diverse ligands, such as phospholipids, oxysterols, sphingolipids, cholesterol, and possibly fatty acids, bind to START domains in mammal and have functions in controlling thioesterase enzyme activity, tumour suppression and non-vesicular lipid transport (Ponting et al 1999;Suricata et al 2000;Roccio et al 2003;Strauss et al 2003).…”