heme-binding beta-barrel domain of human THAP4, Arabidopsis thaliana nitrobindin, and similar proteins
Proteins in this subfamily use a beta-barrel domain to bind ferric heme. This group also includes the beta-barrel domain of human THAP domain containing 4 (THAP4). The THAP domain is found in proteins involved in transcriptional regulation, cell-cycle control, apoptosis and chromatin modification. Arabidopsis thaliana nitrobindin may reversibly bind nitric oxide (NO) and be involved in NO transport. It also includes the beta-barrel domain of Caenorhabditis elegans protein male abnormal 7 (Mab-7) which plays an important role in determining body shape and sensory ray morphology. 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.
Jiyao W et al.(2023). "The conserved domain database in 2023.",