Alpha-2-macroglobulin

Alpha-2-macroglobulin (A2M) is a large protease inhibitor that functions through a distinctive "trapping" mechanism (UniProt: P01023). When proteinases cleave its bait region, the protein undergoes a conformational change that sequesters the enzyme, reducing its activity against high molecular weight substrates while maintaining activity toward smaller substrates. A thioester bond is subsequently hydrolyzed to covalently stabilize the proteinase–protein complex.

A2M is a broad-spectrum inhibitor of all four proteinase classes and plays roles in tissue remodeling and immune regulation across multiple tissues. No specific disease associations are documented in UniProt for this entry.

In Alzheimer's disease, A2M is significantly downregulated in post-mortem AD brain tissue relative to age-matched controls (mean log2 fold-change: −0.37; Chaparral AD proteomics). This downregulation was detected across one fraction in a subcellular proteomics study of human post-mortem brain comparing multiple compartments (P2, P3, S2, S3) using TMT-labeled, data-dependent acquisition mass spectrometry. The reduced A2M levels may reflect impaired protease regulation in the AD brain microenvironment.