Liver fatty acid binding protein (FABP1) is a member of the family of intracellular lipid binding proteins (iLBPs). ILBPs are believed to have a role in solubilisation of poorly water-soluble ligands and in facilitating their transport through the cytosol (1,2). However, it has become increasingly clear in recent years that they also perform specific roles in regulating the biological activities of their ligands. Literature shows that binding of the anti-diabetic drug troglitazone to adipocyte fatty acid binding protein (FABP4) leads to nuclear localization of the complex and subsequent activation of the peroxisome proliferator activated receptor (PPARγ) (3,4). This was proposed to occur through assembly of a conformational nuclear localization signal (NLS) in FABP4 on ligand binding. In our own studies we have demonstrated that FABP1 binds to the PPARα agonist (GW7647) and that FABP1 increases the activity of GW7647 towards PPARα in a cell based assay. However, FABP1 is unable to assemble a conformational NLS as it lacks the necessary positively charged residues in its sequence suggesting that there are different mechanisms that underpin nuclear localization for different FABPs. We hypothesize that GW7647 binding to FABP1 leads structural changes or stabilizes the interaction of the FABP1-GW7647 complex with PPARα which ultimately leads to activation of the receptor.
To understand structural changes in FABP1 upon GW7647 binding, we have determined the structures of apo- and GW7647-bound FABP1. Both the structures were solved using an in-house protocol for fast structure determination of protein structure. We have confirmed a role for FABP1 in solubilization of highly lipophilic GW7647 (clogP: 7.2). In addition we demonstrate that GW7647-binding leads to conformation changes in the structure of FABP1. We suggest that the change in conformation upon complex formation favours an interaction with PPARα that results in receptor activation.