Structural and biochemical characterization and evolutionary relationships of the fatty acid-binding protein 10 (Fabp10) of hake (Merluccius hubbsi)

Fatty acid binding to the human transport proteins FABP3, FABP4, and FABP5 from a Ligand's perspective

Fatty acid binding proteins (FABPs) are a family of amphiphilic transport proteins with high diversity in terms of their amino acid sequences and binding preferences. Beyond their main biological role as cytosolic fatty acid transporters, many aspects regarding their binding mechanism and functional specializations in human cells remain unclear. In this work, the binding properties and thermodynamics of FABP3, FABP4, and FABP5 were analyzed under various physical conditions. For this purpose, the FABPs were loaded with fatty acids bearing fluorescence or spin probes as model ligands, comparing their binding affinities via microscale thermophoresis (MST) and continuous-wave electron paramagnetic resonance (CW EPR) spectroscopy. The CW EPR spectra of non-covalently bound 5- and 16-DOXYL stearic acid (5/16-DSA) deliver in-depth information about the dynamics and chemical environments of ligands inside the binding pockets of the FABPs. EPR spectral simulations allow the construction of binding curves, revealing two different binding states ('intermediately' and 'strongly' bound). The proportion of bound 5/16-DSA depends strongly on the FABP concentration and the temperature but with remarkable differences between the three isoforms. Additionally, the more dynamic state ('intermediately bound') seems to dominate at body temperature with thermodynamic preference. The ligand binding studies were supplemented by aggregation studies via dynamic light scattering and bioinformatic analyses. Beyond the remarkably fine-tuned binding properties exhibited by each FABP, which were discernible with our EPR-centered approach, the results of this work attest to the power of simple spectroscopic experiments to provide new insights into the ligand binding mechanisms of proteins in general on a molecular level.

Molecular Characteristics of the Fatty-Acid-Binding Protein (FABP) Family in Spirometra mansoni-A Neglected Medical Tapeworm

The plerocercoid larva of the tapeworm Spirometra mansoni can parasitize humans and animals, causing serious parasitic zoonosis. The molecular characteristics and adaptive parasitism mechanism of Spirometra tapeworms are still unknown. In this study, 11 new members of the fatty-acid-binding protein (FABP) family were characterized in S. mansoni. A clustering analysis showed 11 SmFABPs arranged into two groups, and motif patterns within each group had similar organizations. RT-qPCR showed that SmFABPs were highly expressed in the adult stage, especially in gravid proglottid. A high genetic diversity of SmFABPs and relative conservation of FABPs in medical platyhelminthes were observed in the phylogenetic analysis. Immunolocalization revealed that natural SmFABP is mainly located in the tegument and parenchymal tissue of the plerocercoid and the uterus, genital pores, and cortex of adult worms. rSmFABP can build a more stable holo form when binding with palmitic acid to protect the hydrolytic sites of the protein. A fatty acid starvation induction test suggested that SmFABP might be involved in fatty acid absorption, transport, and metabolism in S. mansoni. The findings in this study will lay the foundation to better explore the underlying mechanisms of FABPs involved in Spirometra tapeworms as well as related taxa.

Fatty acid-binding protein genes in gilthead seabream: molecular cloning and nutritional regulation under low water temperatures

The molecular characteristics and tissue disruption of 10 fatty acid-binding protein (fabp) genes in gilthead seabream (Sparus aurata) were investigated, and their expression levels were found in the fish fed diets with different vegetable oil (VO) sources, which may explore the potential function of fabp genes in S. aurata. For this purpose, the open reading frames of fabp genes involved in the transport and ß-oxidation of fatty acids (FA) were molecularly cloned and characterized. S. aurata was then exposed to a two-staged feeding trial (the grow-out period following a wash-out period) at low water temperatures. In the grow-out period, the fish were fed diets containing 50% and 100% ratios of various VOs for 60 days, and in the wash-out period, the fish were fed a diet containing 100% fish oil (FO) for 30 days. It has been determined that (a) S. aurata and vertebrate fabp/FABP genes are orthologues; (b) spatio-temporal differences in tissue-specific patterns of fabp genes differ importantly; for instance, the difference between the highest and lowest values reaches 13 × 10⁵ -fold in the fabp10a; and (c) VO-based diets upregulated fabp transcript levels in the liver and muscle with some exceptions, such as liver fabp11a and muscle fabp7a. Gene expressions of only the hepatic fabp7b and fabp10a genes were diminished at the end of the wash-out period. In this study, the authors provide further evidence that dietary FAs affect fabp mRNA expressions in S. aurata. This might be useful in the nutritional control of fabp genes to maintain lipid homeostasis in marine fish fed VO-based diets at low water temperatures.

Tracing the evolution of fatty acid-binding proteins (FABPs) in organisms with a heterogeneous fat distribution

The distribution of fat among both invertebrate and vertebrate groups is heterogeneous. Studies have shown that fatty acid‐binding proteins (FABPs), which mainly bind and transport fatty acids, play important roles in the regulation of fat storage and distribution. However, the systematic and genome‐wide investigation of FABP genes in organisms with a heterogeneous fat distribution remains in its infancy. The availability of the complete genomes of Caenorhabditis elegans, Callorhinchus milii, and other organisms with a heterogeneous fat distribution allowed us to systematically investigate the gene structure and phylogeny of FABP genes across a wide range of phyla. In this study, we analyzed the number, structure, chromosomal location, and phylogeny of FABP genes in 18 organisms from C. elegans to Homo sapiens. A total of 12 types of FABP genes were identified in the 18 species, and no single organism exhibited all 12 fatty acid‐binding genes (FABPs). The absence of a specific FABP gene in tissue may be related to the absence of fat storage in the corresponding tissue. The genomic loci of the FABP genes were diverse, and their gene structures varied. The results of the phylogenetic analysis and the observation of conserved gene synthesis of FABP family genes/proteins suggest that all FABP genes may have evolved from a common ancestor through tandem duplication. This study not only lays a strong theoretical foundation for the study of fat deposition in different organisms, but also provides a new perspective regarding metabolic disease prevention and control and the improvement of agricultural product quality.

Transcriptome analysis of golden pompano (Trachinotus ovatus) liver indicates a potential regulatory target involved in HUFA uptake and deposition

Promoting highly unsaturated fatty acid (HUFA) uptake and deposition can improve nutritional value of farmed fish and reduce dietary fish oil addition. Previously, we found that the golden pompano Trachinotus ovatus liver HUFA content increased with the increasing of dietary HUFA. Therefore, we examined the common genes and pathways responsible for HUFA uptake and deposition in T. ovatus liver using transcriptome sequencing technology after feeding with either 1.0% or 2.1% HUFA for 8 weeks. Results showed that a total of 140 and 147 genes were significantly upregulated and downregulated, respectively. Five bile acid synthesis-related genes (CYP7A1, CYP8B1, AKR1D1, SCP2 and ACOT8), which are related to dietary fat emulsification were downregulated in 2.1% HUFA group, implying that the cholate synthesized through the classical pathway might be the main bile acid form in fat emulsification. Moreover, fatty acid transport protein (FATP)-6, fatty acid binding protein (FABP)-1, -4, and -6 increased with HUFA deposition, especially FATP6 and FABP4, suggesting that the two genes may be important mediators involved in HUFA uptake and deposition. KEGG analysis showed that most of the differential genes described above were involved in peroxisome proliferator activator receptor (PPAR) signaling pathway, and PPARγ increased with HUFA deposition, indicating that PPARγ might be a key regulator of HUFA uptake and deposition by regulating the genes involved in fatty acid emulsification and transport. This study focused on the liver, which is the center of intermediary metabolism, providing a comprehensive understanding of the molecular regulation of HUFA uptake and deposition in T. ovatus, which should be further investigated to develop potential measures to improve HUFA content.

Molecular cloning and tissue distribution of fatty acid binding protein-3 in goldfish (Carassius auratus) and its mRNA expression in response to cadmium and PAMPs

Fatty acid binding proteins (FABPs) are members of the conserved, multigene family of intracellular lipid binding proteins. In this study, the full-length cDNA of goldfish (Carassius auratus) FABP-3 (gfFABP-3) was successfully cloned. gfFABP-3 had an open reading frame of 402 bp and encoded a 133 amino acid polypeptide. The predicted gfFABP-3 protein included a lipocalin domain and displayed typical conserved FABP tertiary structures. Reverse transcription-PCR (RT-PCR) revealed that the gfFABP-3 gene was expressed in all tested tissues, with higher levels of expression in the testis, liver, heart, fat and kidney. After 24 h of cadmium exposure, gfFABP-3 was significantly upregulated in the gill, liver and spleen, but downregulated in the intestine, as compared to unexposed controls. gfFABP-3 expression was significantly downregulated in the spleen in goldfish challenged with LPS and Poly I:C. Our study provides a molecular characterization of goldfish FABP-3 and indicated that gfFABP-3 was potentially associated with the toxic effects of cadmium on lipid metabolism, and with the immune response to pathogenic infection.