Binding of the human antioxidation protein α1-microglobulin (A1M) to heparin and heparan sulfate. Mapping of binding site, molecular and functional characterization, and co-localization in vivo and in vitro

Abstract

Heparin and heparan sulfate (HS) are linear sulfated disaccharide polymers. Heparin is found mainly in mast cells, while heparan sulfate is found in connective tissue, extracellular matrix and on cell membranes in most tissues. α 1 -microglobulin (A1M) is a ubiquitous protein with thiol-dependent antioxidant properties, protecting cells and matrix against oxidative damage due to its reductase activities and radical- and heme-binding properties. In this work, it was shown that A1M binds to heparin and HS and can be purified from human plasma by heparin affinity chromatography and size exclusion chromatography. The binding strength is inversely dependent of salt concentration and proportional to the degree of sulfation of heparin and HS. Potential heparin binding sites, located on the outside of the barrel-shaped A1M molecule, were determined using hydrogen deuterium exchange mass spectrometry (HDX-MS). Immunostaining of endothelial cells revealed pericellular co-localization of A1M and HS and the staining of A1M was almost completely abolished after treatment with heparinase. A1M and HS were also found to be co-localized in vivo in the lungs, aorta, kidneys and skin of mice. The redox-active thiol group of A1M was unaffected by the binding to HS, and the cell protection and heme-binding abilities of A1M were slightly affected. The discovery of the binding of A1M to heparin and HS provides new insights into the biological role of A1M and represents the basis for a novel method for purification of A1M from plasma.

Ferryl Hemoglobin and Heme Induce A1-Microglobulin in Hemorrhaged Atherosclerotic Lesions with Inhibitory Function against Hemoglobin and Lipid Oxidation

“…Given that both oxidative stress [48,49] and hemorrhage [10,18] play a significant role in atherosclerosis, it is reasonable to assume that A1M, due to its pronounced radical-scavenging and heme-binding, represents a protective response to plaque progression. The presence of A1M in the arterial wall was recently also demonstrated with mouse aortas using immunofluorescence [50]. In this report, a strong A1M-staining was seen on the luminal surface of the endothelium, besides a sub-endothelial localization, and the A1M-activity was co-localized with heparan-sulfate.…”

Kidney Protection with the Radical Scavenger α1-Microglobulin (A1M) during Peptide Receptor Radionuclide and Radioligand Therapy

“…Thus, A1M is found in the extracellular fluids of all tissues surrounding epithelial cells. It has been shown to be particularly abundant in extracellular matrix, on cell surfaces, and at blood vessel basal membranes [ 101 ], partly due to its affinity for collagen and heparin [ 102 , 103 ]. As a result of its relatively small size, the protein is cleared from the blood circulation by the kidneys through glomerular filtration followed by reabsorption and degradation in the proximal tubular cells ( Figure 3 ) [ 104 ].…”