A) α-helical regions of ILPs with described NLS (human CRABPII, FABP4 and FABP5) are shown aligned with human (FABP2) and Danio rerio FABP2 (Fabp2). Basic amino acids that compose the NLS are highlighted in bold. B) Superimposed structures of human apoFABP4 (3rzy.pdb) and human apoFABP2 (1kzw.pdb) α-helical region. Side chains of NLS amino acids are shown for human FABP4 (magenta) and human FABP2 (blue).

A) Graphical representation of nuclear/cytoplasmic fluorescence intensity ratio (mean ± SD) of wild-type, ¹⁷A²⁹A³⁰A, ¹⁷A²⁸A²⁹A, ¹⁷A and ²⁸A²⁹A Fabp2-EGFP in Caco-2 cells. Statistical significance of each mutant with respect to wild-type Fabp2 is indicated when corresponds, **** p < 0.0001, ** p < 0.01, * p < 0.05. B) Representative single focal planes of Caco-2 cells transfected with wild-type, ¹⁷A²⁹A³⁰A, ¹⁷A²⁸A²⁹A, ¹⁷A or ²⁸A²⁹A Fabp2-EGFP (green). Nuclear DAPI counterstaining (blue) is also shown. Bar: 10 μm.

A) SDS-PAGE of purified wild-type (lane 2), ¹⁷A²⁹A³⁰A (lane 3) and ¹⁷A²⁸A²⁹A (lane 4) drFabp2. The molecular weight of the proteins is indicated in kDa in Standard (lane 1). B) Circular dichroism analysis of wild-type, ¹⁷A²⁹A³⁰A and ¹⁷A²⁸A²⁹A drFabp2 in the far- (185–235 nm) and near- (250–320 nm) UV spectra. C) wild-type, ¹⁷A²⁹A³⁰A and ¹⁷A²⁸A²⁹R drFabp2-BODIPY FL C16 binding affinity determination. Fluorescence intensity values were recorded at 510 nm (λex) and 530 nm (λem) using 0.5 μM of each protein.

A) Graphical representation of nuclear/cytoplasmic fluorescence intensity ratio (mean ± SD) of wild type Fabp2-EGFP in Caco-2 cells cultured in media with vehicle or in media with 40 μM Importazole. B) Representative single focal planes of Caco-2 cells transfected with wild type Fabp2-EGFP (green) cultured in media with vehicle or in media with 40 μM Importazole. Nuclei counterstaining with DAPI is shown in blue. C) Representative single focal planes of anti-c-Myc signal (gray) in Caco-2 cells cultured in media with vehicle or in media with 40 μM Importazole. Nuclei counterstaining with DAPI is shown in blue. Arrow points to a c-Myc positive nucleus. Bar: 10 μm.

A) Superimposed structures of the α-helical regions of mFABP4 bound to linolenic acid (mFABP4-LA, PDB ID: 2Q9S), mFABP4 bound to oleic acid (mFABP4-OA, PDB ID: 1LID) and hFABP2 bound to oleic acid (hFABP2-OA, PDB ID: 2MO5) α-helical region. The side chain of the Phe residue implicated in ligand-dependent response to ligands is shown for FABP4 bound to linolenic acid (blue), mFABP4 bound to oleic acid (green) and hFABP2 bound to oleic acid (red). B) Graphical representation of nuclear/cytoplasmic fluorescence intensity relationship (mean ± SD) of wild- type and ¹⁷A²⁸A²⁹A drFabp2-EGFP in Caco-2 cells cultured in media without FBS (-FBS) or in media without FBS and with oleic acid (-FBS/+OA). Statistical significance is indicated, **** p < 0.0001, n.s. not significant. C) Representative single focal planes of Caco-2 cells transfected with wild- type or ¹⁷A²⁸A²⁹A drFabp2-EGFP (green) cultured in media without FBS (-FBS) or in media without FBS and with oleic acid (-FBS/+OA). Nuclei counterstaining with DAPI is shown in blue. Bar: 10 μm.