Insight into the interaction sites between fatty acid binding proteins and their ligands

• Published in: Journal of molecular modeling 2010-05, Vol.16 (5), p.929-938
• Main Authors: Levin, Lihie Ben-Avraham, Ganoth, Assaf, Amram, Shay, Nachliel, Esther, Gutman, Menachem, Tsfadia, Yossi
• Format: Article
• Language: English
• Subjects: Animals; Binding Sites - genetics; Bufonidae; Carrier Proteins - analysis; Carrier Proteins - genetics; Carrier Proteins - metabolism; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Chickens; Computer Appl. in Life Sciences; Computer Applications in Chemistry; Fatty Acid-Binding Proteins - analysis; Fatty Acid-Binding Proteins - genetics; Fatty Acid-Binding Proteins - metabolism; Fatty Acids - chemistry; Fatty Acids - genetics; Fatty Acids - metabolism; Ligands; Liver - chemistry; Liver - metabolism; Membrane Glycoproteins - analysis; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Molecular Dynamics Simulation; Molecular Medicine; Original Paper; Theoretical and Computational Chemistry
• ISSN: 1610-2940; 0948-5023
• DOI: 10.1007/s00894-009-0599-6

Fatty acid binding proteins (FABPs), are evolutionarily conserved small cytoplasmic proteins that occur in many tissue-specific types. One of their primary functions is to facilitate the clearance of the cytoplasmic matrix from free fatty acids and of other detergent-like compounds. Crystallographic studies of FABP proteins have revealed a well defined binding site located deep inside their β-clam structure that is hardly exposed to the bulk solution. However, NMR measurements revealed that, when the protein is equilibrated with its ligands, residues that are clearly located on the outer surface of the protein do interact with the ligand. To clarify this apparent contradiction we applied molecular dynamics simulations to follow the initial steps associated with the FABP–fatty acid interaction using, as a model, the interaction of toad liver basic FABP, or chicken liver bile acid binding protein, with a physiological concentration of palmitate ions. The simulations (~200 ns of accumulated time) show that fatty acid molecules interact, unevenly, with various loci on the protein surface, with the favored regions being the portal and the anti-portal domains. Random encounters with palmitate at these regions led to lasting adsorption to the surface, while encounters at the outer surface of the β-clam were transient. Therefore, we suggest that the protein surface is capable of sequestering free fatty acids from solution, where brief encounters evolve into adsorbed states, which later mature by migration of the ligand into a more specific binding site.