Expression and purification of Drosophila OBP44a with the aids of LC-MS and NMR

Evaluating the use of lanthanide containing dendrimers for solvent paramagnetic relaxation enhancement

Paramagnetic relaxation enhancement (PRE) is widely used in biomolecular NMR spectroscopy to obtain long-range distance and orientational information for intra- or intermolecular interactions. In contrast to conventional PRE measurements, which require tethering small molecules containing either a radical or paramagnetic ion to specific sites on the target protein, solvent PRE (sPRE) experiments utilize paramagnetic cosolutes to induce a delocalized PRE effect. Compounds developed as contrast agents in magnetic resonance imaging (MRI) applications typically consist of Gd chelated by a small molecule. Coordinating these Gd-containing small molecules to larger and inert scaffolds has been shown to increase the PRE-effect and produce more effective contrast agents in MRI. Inspired by their use as MRI contrast agent, in this work we evaluate the effectiveness of using a functionalized polyamidoamine (PAMAM) dendrimer for sPRE measurements. Using ubiquitin as a model system, we measured the sPRE effect from a generation 5 PAMAM dendrimer (G5-Gd) as a function of temperature and pH and compared to conventional relaxation agents. We also demonstrated the utility of G5-Gd in sPRE studies to monitor changes in the structures of two proteins as they bind their ligands. These studies highlight the attractive properties of these macromolecular relaxation agents in biomolecular sPRE.

NMR chemical shift assignment of Drosophila odorant binding protein 44a in complex with 8(Z)-eicosenoic acid

The odorant binding protein, OBP44a is one of the most abundant proteins expressed in the brain of the developing fruit fly Drosophila melanogaster. Its cellular function has not yet been determined. The OBP family of proteins is well established to recognize hydrophobic molecules. In this study, NMR is employed to structurally characterize OBP44a. NMR chemical shift perturbation measurements confirm that OBP44a binds to fatty acids. Complete assignments of the backbone chemical shifts and secondary chemical shift analysis demonstrate that the apo state of OBP44a is comprised of six α-helices. Upon binding 8(Z)-eicosenoic acid (8(Z)-C20:1), the OBP44a C-terminal region undergoes a conformational change, from unstructured to α-helical. In addition to C-terminal restructuring upon ligand binding, some hydrophobic residues show dramatic chemical shift changes. Surprisingly, several charged residues are also strongly affected by lipid binding. Some of these residues could represent key structural features that OBP44a relies on to perform its cellular function. The NMR chemical shift assignment is the first step towards characterizing the structure of OBP44a and how specific residues might play a role in lipid binding and release. This information will be important in deciphering the biological function of OBP44a during fly brain development.

Glia-derived secretory fatty acid binding protein Obp44a regulates lipid storage and efflux in the developing Drosophila brain

Glia derived secretory factors play diverse roles in supporting the development, physiology, and stress responses of the central nervous system (CNS). Through transcriptomics and imaging analyses, we have identified Obp44a as one of the most abundantly produced secretory proteins from Drosophila CNS glia. Protein structure homology modeling and Nuclear Magnetic Resonance (NMR) experiments reveal Obp44a as a fatty acid binding protein (FABP) with a high affinity towards long-chain fatty acids in both native and oxidized forms. Further analyses demonstrate that Obp44a effectively infiltrates the neuropil, traffics between neuron and glia, and is secreted into hemolymph, acting as a lipid chaperone and scavenger to regulate lipid and redox homeostasis in the developing brain. In agreement with this essential role, deficiency of Obp44a leads to anatomical and behavioral deficits in adult animals and elevated oxidized lipid levels. Collectively, our findings unveil the crucial involvement of a noncanonical lipid chaperone to shuttle fatty acids within and outside the brain, as needed to maintain a healthy brain lipid environment. These findings could inspire the design of novel approaches to restore lipid homeostasis that is dysregulated in CNS diseases.