Ligand binding-dependent functions of the lipocalin NLaz: an in vivo study in Drosophila

Abstract

Lipocalins are small extracellular proteins mostly described as lipid carriers. The Drosophila lipocalin NLaz (neural Lazarillo) modulates the IIS pathway and regulates longevity, stress resistance, and behavior. Here, we test whether a native hydrophobic pocket structure is required for NLaz to perform its functions. We use a point mutation altering the binding pocket (NLaz L130R) and control mutations outside NLaz binding pocket. Tryptophan fluorescence titration reveals that NLazL130R loses its ability to bind ergosterol and the pheromone 7(z)-tricosene but retains retinoic acid binding. Using site-directed transgenesis in Drosophila, we test the functionality of the ligand binding-altered lipocalin at the organism level. NLaz-dependent life span reduction, oxidative stress and starvation sensitivity, aging markers accumulation, and deficient courtship are rescued by overexpression of NLaz WT, but not of NLazL130R. Transcriptional responses to aging and oxidative stress show a large set of age-responsive genes dependent on the integrity of NLaz binding pocket. Inhibition of IIS activity and modulation of oxidative stress and infection- responsive genes are binding pocket-dependent processes. Control of energy metabolites on starvation appears to be, however, insensitive to the modification of the NLaz binding pocket. © FASEB.