lipocalin domain of alpha1-microglobulin and similar proteins
Alpha(1)-microglobulin (A1M, also known as protein AMBP, alpha-1 microglycoprotein, and protein HC), has immunosuppressive properties, such as inhibition of antigen induced lymphocyte cell-proliferation, cytokine secretion, and oxidative burst of neutrophils. A1M may participate in the reducing and scavenging of biological pro-oxidants such as heme and heme-proteins. It binds heme strongly, and a C-terminally processed form of the protein degrades the heme. It can reduce cytochrome C, nitroblue tetrazolium, methemoglobin and free iron, using NADH, NADPH or ascorbate as cofactor. Intravenous administration of recombinant A1M in animal models eliminates or significantly reduces the manifestations of preeclampsia. A1M is a useful biomarker in clinical diagnostics for monitoring pre-eclampsia, hepatitis E, renal tubular dysfunction, and renal toxicity. A1M 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
Jiyao W et al.(2023). "The conserved domain database in 2023.",