BPS2026 – Structure determination of odorant-binding protein, OBP44a, and NMR characterization of fatty acid binding related to variable pH

Drosophila melanogaster (fruit fly) shares approximately 75% of genes involved in human genetic diseases and completes a life cycle in 10–14 days, making it a useful generational model to explore phenotypes associated with amino acid mutations. Odorant-binding proteins (OBPs) are a family of proteins known to bind hydrophobic molecules in fruit flies and other insects, typically acting as chemosensors. This study focuses on OBP44a, a 14kD helical protein identified in Drosophila melanogaster , which is highly expressed in the fly brain during early development. This localization points to a non-chemosensory role associated with hydrophobic ligand shuttling, cellular signaling or maintaining homeostatic processes via ligand transport intra- and extra-cellularly. Prior studies have shown that OBP44a undergoes a conformational change upon fatty acid binding, which involves the formation of a 7 th α-helix relative to the protein’s apo state. These studies are advanced here by the NMR structure determination of OBP44a bound to eicosenoic acid, (8Z)C20:1, at pH 6.6. In addition to structure elucidation, fatty acid-binding assay results are presented here, along with identification of residues sensitive to pH, as well as the pH dependence of ligand release. Specifically, the apo form of OBP44a begins to appear at lower pH and seems to involve residues not directly involved in ligand contacts, suggesting an allosteric mechanism that may be utilized in the fly to deliver fatty acid cargo in the developing brain.