Review: the liver bile acid-binding proteins

Area of Science:

• Biochemistry
• Molecular Biology
• Comparative Physiology

Background:

• Liver bile acid-binding proteins (L-BABPs), a subfamily of fatty acid-binding proteins (FABPs), possess a conserved beta-barrel structure.
• L-BABPs are present in the liver of various vertebrates, including fish, amphibians, reptiles, and birds, but are notably absent in mammals.

Purpose of the Study:

• To summarize the structural and functional characteristics of L-BABPs.
• To highlight the evolutionary distribution of L-BABPs across vertebrate species.
• To identify the knowledge gap regarding mammalian homologs and their functions.

Main Methods:

• Review of existing literature on L-BABP structure and function.
• Analysis of X-ray crystallography and NMR spectroscopy data for L-BABP.
• Comparative analysis of FABP families across vertebrate taxa.

Main Results:

• L-BABPs exhibit a characteristic 10-stranded beta-barrel fold with two inserted helices.
• Ligand binding stoichiometry for bile acids is typically 2:1 (cholates:protein), except for zebrafish L-BABP (1:1) due to a disulfide bridge.
• Fatty acid binding stoichiometry is consistently 1:1.

Conclusions:

• The structural and ligand-binding properties of L-BABPs are well-characterized.
• The absence of L-BABPs in mammals suggests the existence of alternative proteins performing similar functions.
• Identifying the mammalian functional equivalent of L-BABPs is a critical area for future research.