FIGURE 2.

Model of Fabp function. Fabps function as sensors, conveyors and modulators of cellular function. Small hydrophobic molecules (e.g. fatty acids, bile acids) that serve as Fabp ligands (black circle) enter cells via solute transporters (represented in green), or partition into the plasma membrane, are taken up by Fabps (represented in light brown). Each Fabp type has distinct ligand preferences as well as preferred protein binding partners (e.g. represented in orange and cyan in the figure) with different affinities for unliganded and liganded Fabps. Liganded Fabps transport their cargos to their sites of utilization. These include the nucleus (represented in purple) and other organelles (represented in beige). In the nucleus, Fabps interact with a variety of transcription factors (represented in blue), including but not limited to nuclear receptors which accept their cargos, to regulate the expression of their target genes. Fabp ligands conveyed into the nucleus may leave the nucleus via Fabps. In other organelles, both unliganded and liganded Fabps can interact with the cytosolic domains of membrane‐bound transmembrane proteins to modulate their activities (organellar transmembrane proteins represented in orange; plasma membrane transmembrane proteins represented in cyan). Fabp ligands delivered to organelles can be metabolized (e.g. fatty acids converted to triacylglycerols for storage or oxidized for energy). Alternatively, fatty acids released during hydrolysis of triacylglycerols, or other fatty acid esters, can be captured by Fabps and conveyed to other sites of utilization. Fabps may offload their cargos to various membrane systems (plasma and organellar membranes) by desorption, or via membrane‐bound transporters. Cellular export of Fabp ligands can be achieved by interaction of the liganded Fabp with plasma membrane‐localized solute exporters (e.g. represented in green at the bottom of figure).