Stark, Ruth E. Molecular Drivers of FABP-mediated Endocannabinoid Signaling for Appetite Regulation Metabolic signaling by endogenous cannabinoids (ECs) is essential to the regulation of human appetite, pain, and neuroprotection. Fatty acid-binding proteins (FABPs) can either sequester the hydrophobic ECs or transport them to hydrolytic enzymes; ECs routed to the nucleus also activate the peroxisome proliferator-activated receptors (PPARs). EC levels have been correlated with obesity in knockout mice for liver (L) FABP that is co-expressed with intestinal (I) FABP in enterocytes and also for PPARa knockouts, underscoring the regulatory roles of these proteins. We will probe poorly understood EC-FABP, EC-PPAR, and FABP-EC-PPAR complexes in vitro at near-physiological concentrations, determining affinities, metabolic fates, molecular binding interfaces, and conformational changes to test mechanistic hypotheses regarding EC signaling. Trainees at multiple career stages, including those recruited from underrepresented groups in STEM, will be integrally involved in this research program. Specific questions to be addressed are as follows: (1) How do ECs choose between FABP chaperones to produce obese or lean outcomes? The possibility that ECs are delivered by LFABP to hydrolytic enzymes for metabolic breakdown rather than sequestered by IFABP in the enterocyte will be tested enzymatically, whereas the rationale for LFABP’s diminished affinity will be explored using high- pressure solution-state NMR to identify energetically favored candidate sites for binding. (2) Could transcriptional activity be driven by EC binding preferences for LFABP vs. PPARa? The PPARa ligand-binding domain (PPARa_LBD) will be purified, rigorously delipidated, and tested in vitro for EC- modulated transcriptional activity. EC binding affinities will be compared for PPARa_LBD and FABPs. (3) Could transcriptional activity be driven by EC-modulated FABP-PPAR collisions that cause conformational changes? To determine the interactions involved in the proposed FABP-mediated EC activation of PPARa transcriptional function, we will first use surface plasmon resonance to measure the binding affinity of LFABP-PPARa_LBD protein complexes, on their own and in the presence of ligands with a range of known activation efficacies. The site-specific collision-associated impact on the LFABP partner will be probed by solution-state NMR spectroscopy of the [U-15N]-enriched protein, using chemical shift perturbations of each backbone NH resonance to define the binding interface with PPARa_LBD, any allosteric structural changes that occur upon complex formation, and their modulation by EC ligands. Taken together, these experiments will advance our understanding of (macro)molecular networks that function to achieve metabolic signaling by ECs involved in appetite and pain regulation, thereby advancing our understanding of health risks related to obesity and inflammation. This understanding can guide...