Interaction of chicken liver basic fatty acid-binding protein with fatty acids: a 13C NMR and fluorescence study

All-Purpose Containers? Lipid-Binding Protein - Drug Interactions

The combined use of in vitro (¹⁹F-NMR) and in silico (molecular docking) procedures demonstrates the affinity of a number of human calycins (lipid-binding proteins from ileum, liver, heart, adipose tissue and epidermis, and retinol-binding protein from intestine) for different drugs (mainly steroids and vastatins). Comparative evaluations on the complexes outline some of the features relevant for interaction (non-polar character of the drugs; amino acids and water molecules in the protein calyx most often involved in binding). Dissociation constants (K_i) for drugs typically lie in the same range as K_i for natural ligands; in most instances (different proteins and docking conditions), vastatins are the strongest interactors, with atorvastatin ranking top in half of the cases. The affinity of some calycins for some of the vastatins is in the order of magnitude of the drug C_max after systemic administration in humans. The possible biological implications of this feature are discussed in connection with drug delivery parameters (route of administration, binding to carrier proteins, distribution to, and accumulation in, human tissues).

Bile salt recognition by human liver fatty acid binding protein

Fatty acid binding proteins (FABPs) act as intracellular carriers of lipid molecules, and play a role in global metabolism regulation. Liver FABP (L-FABP) is prominent among FABPs for its wide ligand repertoire, which includes long-chain fatty acids as well as bile acids (BAs). In this work, we performed a detailed molecular- and atomic-level analysis of the interactions established by human L-FABP with nine BAs to understand the binding specificity for this important class of cholesterol-derived metabolites. Protein-ligand complex formation was monitored using heteronuclear NMR, steady-state fluorescence spectroscopy, and mass spectrometry. BAs were found to interact with L-FABP with dissociation constants in the narrow range of 0.6-7 μm; however, the diverse substitution patterns of the sterol nucleus and the presence of side-chain conjugation resulted in complexes endowed with various degrees of conformational heterogeneity. Trihydroxylated BAs formed monomeric complexes in which single ligand molecules occupied similar internal binding sites, based on chemical-shift perturbation data. Analysis of NMR line shapes upon progressive addition of taurocholate indicated that the binding mechanism departed from a simple binary association equilibrium, and instead involved intermediates along the binding path. The co-linear chemical shift behavior observed for L-FABP complexes with cholate derivatives added insight into conformational dynamics in the presence of ligands. The observed spectroscopic features of L-FABP/BA complexes, discussed in relation to ligand chemistry, suggest possible molecular determinants of recognition, with implications regarding intracellular BA transport. Our findings suggest that human L-FABP is a poorly selective, universal BA binder.

Review: the liver bile acid-binding proteins

The liver bile acid-binding proteins, L-BABPs, formerly called the liver "basic" fatty acid-binding proteins, are a subfamily of the fatty acid-binding proteins, FABPs. All the members of this protein group share the same fold: a 10 stranded beta barrel in which two short helices are inserted in between the first and the second strand of antiparallel beta sheet. The barrel encloses the ligand binding cavity of the protein while the two helices are believed to be involved in ligand accessibility to the binding site. The L-BABP subfamily has been found to be present in the liver of several vertebrates: fish, amphibians, reptiles, and birds but not in mammals. The members of the FABP family present in mammals that appear to be more closely related to the L-BABPs are the liver FABPs and the ileal BABPs, both very extensively studied. Several L-BABP X-ray structures are available and chicken L-BABP has also been studied using NMR spectroscopy. The stoichiometry of ligand binding for bile acids, first determined by X-ray crystallography for the chicken liver protein, is of two cholates per protein molecule with the only exception of zebrafish L-BABP which, due to the presence of a disulfide bridge, has a stoichiometry of 1:1. The stoichiometry of ligand binding for fatty acids, determined with several different techniques, is 1:1. An unanswered question of great relevance is the identity of the protein that in mammals performs the function that in other vertebrates is carried out by the L-BABPS.

A single amino acid mutation in zebrafish (Danio rerio) liver bile acid-binding protein can change the stoichiometry of ligand binding

In all of the liver bile acid-binding proteins (L-BABPs) studied so far, it has been found that the stoichiometry of binding is of two cholate molecules per internal binding site. In this paper, we describe the expression, purification, crystallization, and three-dimensional structure determination of zebrafish (Danio rerio) L-BABP to 1.5A resolution, which is currently the highest available for a protein of this family. Since we have found that in zebrafish, the stoichiometry of binding in the protein cavity is of only one cholate molecule per wild type L-BABP, we examined the role of two crucial amino acids present in the binding site. Using site-directed mutagenesis, we have prepared, crystallized, and determined the three-dimensional structure of co-crystals of two mutants. The mutant G55R has the same stoichiometry of binding as the wild type protein, whereas the C91T mutant changes the stoichiometry of binding from one to two ligand molecules in the cavity and therefore appears to be more similar to the other members of the L-BABP family. Based on the presence or absence of a single disulfide bridge, it can be postulated that fish should bind a single cholate molecule, whereas amphibians and higher vertebrates should bind two. Isothermal titration calorimetry has also revealed the presence in the wild type protein and the G55R mutant of an additional binding site, different from the first and probably located on the surface of the molecule.

The interaction between N-n-undecyl-N'-(sodium p-aminobenzenesulfonate) thiourea and serum albumin studied using various spectroscopies and the molecular modeling method

The preparation and characteristics of N-n-undecyl-N'-(sodium-p-aminobenzenesulfonate) thiourea (UPT), a new water-soluble reagent with a saturated fatty hydrocarbon group, were described. The interactions of UPT with bovine serum albumin (BSA) and human serum albumin (HSA) were studied using fluorescence spectroscopy in combination with ultraviolet (UV) absorption spectroscopy, circular dichroism (CD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and the molecular modeling method. UPT exhibited a strong ability to quench the intrinsic fluorescence of both BSA and HSA through a static quenching procedure. The binding constants of UPT and BSA or HSA were determined at different temperatures based on the relevant fluorescence data. The binding sites were obtained and the acting force was suggested to be mainly hydrophobic interaction, which was consistent with the result of the molecular modeling study, and there were also a number of hydrogen bonds between UPT and HSA. The results of determination of the proteins in bovine serum or human serum by this method were very close to those obtained by using Coomassie Brilliant Blue G-250 colorimetry. A practical method was proposed for the determination of UPT in bovine serum or human serum samples with satisfactory results.

Crystal structure of axolotl (Ambystoma mexicanum) liver bile acid-binding protein bound to cholic and oleic acid

The family of the liver bile acid-binding proteins (L-BABPs), formerly called liver basic fatty acid-binding proteins (Lb-FABPs) shares fold and sequence similarity with the paralogous liver fatty acid-binding proteins (L-FABPs) but has a different stoichiometry and specificity of ligand binding. This article describes the first X-ray structure of a member of the L-BABP family, axolotl (Ambystoma mexicanum) L-BABP, bound to two different ligands: cholic and oleic acid. The protein binds one molecule of oleic acid in a position that is significantly different from that of either of the two molecules that bind to rat liver FABP. The stoichiometry of binding of cholate is of two ligands per protein molecule, as observed in chicken L-BABP. The cholate molecule that binds buried most deeply into the internal cavity overlaps well with the analogous bound to chicken L-BABP, whereas the second molecule, which interacts with the first only through hydrophobic contacts, is more external and exposed to the solvent.

Survey of binding properties of fatty acid-binding proteins

Fatty acid-binding proteins (FABPs) are members of a super family of lipid-binding proteins, and occur intracellularly in vertebrates and invertebrates. This review briefly addresses the structural and molecular properties of the fatty acid binding proteins, together with their potential physiological role. Special attention is paid to the methods used to study the binding characteristics of FABPs. An overview of the conventional (Lipidex, the ADIFAB and ITC) and innovative separation-based techniques (chromatographic and electrophoretic methods) for the study of ligand-protein interactions is presented along with a discussion of their strengths, weak points and potential applications. The best conventional approaches with natural fatty acids have generally revealed only limited information about the interactions of fatty acid proteins. In contrast, high-performance affinity chromatography (HPAC) studies of several proteins provide full information on the binding characteristics. The review uses, as an example, the application of immobilized liver basic FABP as a probe for the study of ligand-protein binding by high-performance affinity chromatography. The FABP from chicken liver has been immobilized on aminopropyl silica and the developed stationary phase was used to examine the enantioselective properties of this protein and to study the binding of drugs to FABP. In order to clarify the retention mechanism, competitive displacement studies were also carried out by adding short chain fatty acids to the mobile phase as displacing agents and preliminary quantitative structure-retention relationship (QSRRs) correlations were developed to describe the nature of the interactions between the chemical structures of the analytes and the observed chromatographic results. The results of these studies may shed light on the proposed roles of these proteins in biological systems and may find applications in medicine and medicinal chemistry. This knowledge will yield a deeper insight into the mechanism of fatty acid binding in order to indisputably show the central role played by FABPs in cellular FA transport and utilization for a proper lipid metabolism.

Interactions of chicken liver basic fatty acid-binding protein with lipid membranes

The interactions of chicken liver basic fatty acid-binding protein (Lb-FABP) with large unilamellar vesicles (LUVs) of palmitoyloleoyl phosphatidylcholine (POPC) and palmitoyloleoyl phosphatidylglycerol (POPG) were studied by binding assays, Fourier transform infrared (FT-IR) spectroscopy, monolayers at air-water interface, and low-angle X-ray diffraction. Lb-FABP binds to POPG LUVs at low ionic strength but not at 0.1 M NaCl. The infrared (IR) spectra of the POPG membrane-bound protein showed a decrease of the band corresponding to beta-structures as compared to the protein in solution. In addition, a cooperative decrease of the beta-edge band above 70 degrees C in solution was also evident, while the transition was less cooperative and took place at lower temperature for the POPG membrane-bound protein. Low- and wide-angle X-ray diffraction experiments with lipid multilayers indicate that binding of the protein produces a rearrangement of the membrane structure, increasing the interlamellar spacing and decreasing the compactness of the lipids.