Lipocalin odorant-binding protein and similar proteins
Odorant-binding proteins (OBPs) transport small hydrophobic molecules in the nasal mucosa of vertebrates. This subfamily includes mouse odorant-binding protein 1a (Obp1a), Obp1b, and probasin. Mouse Obp1a and Obp1b, which are expressed in the nasal mucosa, bind the chemical odorant 2-isobutyl-3-methoxypyrazine, and may form a OBPO1a/Opb1B heterodimer. Mouse probasin may play a role in the biology of the prostate gland. This group also includes hamster female-specific lacrimal gland protein (FLP) and aphrodisin. FLP may bind tear lipids or lipid-like pheromones found in hamster tears; aphrodisin is found in hamster vaginal discharge, carries pheromones, and stimulates copulatory behavior in males. This group also includes dog allergen Ca f4 which is expressed by tongue epithelial tissue and found in saliva and dander. Bovine OBP is believed to act as a homodimer, having the C-terminal alpha-helix of each monomer stacking against the beta-barrel of the other monomer; this is possible due to its lack of cysteines and therefore lack of disulfide bonds. This group belongs to the lipocalin/cytosolic fatty-acid binding protein family which have a large beta-barrel ligand-binding cavity. Lipocalins are mainly low molecular weight extracellular proteins that bind principally small hydrophobic ligands, and form covalent or non-covalent complexes with soluble macromolecules, as well as membrane bound-receptors. They participate in processes such as ligand transport, modulation of cell growth and metabolism, regulation of immune response, smell reception, tissue development and animal behavior. Cytosolic fatty-acid binding proteins, also bind hydrophobic ligands in a non-covalent, reversible manner, and have been implicated in intracellular uptake, transport and storage of hydrophobic ligands, regulation of lipid metabolism and sequestration of excess toxic fatty acids, as well as in signaling, gene expression, inflammation, cell growth and proliferation, and cancer development.
Comment:hydrophobic cavity binds different hydrophobic ligands; ligands are bound within the beta-barrel in a central internal water-filled cavity lined with polar and hydrophobic amino acids
Comment:some in this group such as bovine odorant-binding protein are dimeric and lack disulfide bonds, others are monomeric and have disulfide bond(s) such as porcine odorant binding protein
Structure:1HN2; Bos taurus odorant binding protein homodimer bound with 1-aminoanthracene, contacts at 4A
Jiyao W et al.(2023). "The conserved domain database in 2023.",