Lipid‐binding properties of human ApoD and Lazarillo‐related lipocalins: functional implications for cell differentiation

Abstract

Lipocalins are a family of proteins characterized by a conserved eightstranded b-barrel structure with a ligand-binding pocket. They perform a wide range of biological functions and this functional multiplicity must relate to the lipid partner involved. Apolipoprotein D (ApoD) and its insect homologues, Lazarillo (Laz) and neural Lazarillo (NLaz), share common ancestral functions like longevity, stress resistance and lipid metabolism regulation, coexisting with very specialized functions, like courtship behavior. Using tryptophan fluorescence titration, we screened the binding of 15 potential lipid partners for NLaz, ApoD and Laz and uncovered several novel ligands with apparent dissociation constants in the low micromolar range. Retinoic acid (RA), retinol, fatty acids and sphingomyelin are shared ligands. Sterols, however, showed a species-specific binding pattern: cholesterol did not show strong binding to human ApoD, whereas NLaz and Laz did bind ergosterol. Among the lipocalin-specific ligands, we found that ApoD selectively binds the endocannabinoid anandamide but not 2-acylglycerol, and that NLaz binds the pheromone 7-tricosene, but not 7,11-heptacosadiene or 11-cis-vaccenyl acetate. To test the functional relevance of lipocalin ligand binding at the cellular level, we analyzed the effect of ApoD, Laz and NLaz preloaded with RA on neuronal differentiation. Our results show that ApoD is necessary and sufficient to allow for RA differentiating activity. Both human ApoD and Drosophila NLaz successfully deliver RA to immature neurons, driving neurite outgrowth. We conclude that ApoD, NLaz and Laz bind selectively to a different but overlapping set of lipid ligands. This multispecificity can explain their varied physiological functions.

Apolipoprotein D modulates amyloid pathology in APP/PS1 Alzheimer's disease mice

“…Progesterone, AA and retinoic acid bind to the apoD binding pocket with high affinity whereas pregnenolone and specific eicosanoids (e.g. 12-HETE and 5,15-diHETE) also bind but with reduced affinity (Dilley et al, 1990;Lea, 1988;Morais Cabral et al, 1995;Ruiz et al, 2013). In addition to the binding pocket, apoD may also interact with lipids via a cluster of "exposed" hydrophobic residues residing in 3 of its extended loops (Eichinger et al, 2007;Oakley et al, 2012).…”

Exceptionally long 5′ UTR short tandem repeats specifically linked to primates

“…For example, the ancient apolipoprotein D (APOD) and fibroblast growth factor 4 (FGF4) are involved in neuronal differentiation (Ruiz et al, 2013;Kosaka et al, 2006). In another example, a defect in filamin A interacting protein 1-like (FILIP1L), is association with craniofacial abnormalities (Beaty et al, 2013).…”

Schwann cell-derived Apolipoprotein D controls the dynamics of post-injury myelin recognition and degradation

“…For the exogenous addition of ApoD, human ApoD purified from breast cystic fluid (Ruiz et al, 2013) was added at different concentrations (10–100 nM) to the myelin preparation 5 min before its addition to the macrophage culture.…”