biostudies-literatureHarwood SLLEO FoundationNovo Nordisk Fonden16732-16742https://www.ebi.ac.uk/biostudies/studies/S-EPMC7864068biostudies-literatureUnknown295(49)Proteins in the α-macroglobulin (αM) superfamily use thiol esters to form covalent conjugation products upon their proteolytic activation. αM protease inhibitors use theirs to conjugate proteases and preferentially react with primary amines (<i>e.g.</i> on lysine side chains), whereas those of αM complement components C3 and C4B have an increased hydroxyl reactivity that is conveyed by a conserved histidine residue and allows conjugation to cell surface glycans. Human α₂-macroglobulin-like protein 1 (A2ML1) is a monomeric protease inhibitor but has the hydroxyl reactivity-conveying histidine residue. Here, we have investigated the role of hydroxyl reactivity in a protease inhibitor by comparing recombinant WT A2ML1 and the A2ML1 H1084N mutant in which this histidine is removed. The Journal of biological chemistryα₂-Macroglobulin-like protein 1 can conjugate and inhibit proteases through their hydroxyl groups, because of an enhanced reactivity of its thiol ester.PMC7864068NNF18OC0032724LF18039Nielsen NSHarwood SLEnghild JJNielsen PKThogersen IBJensen KTfalseα₂-Macroglobulin-like protein 1 can conjugate and inhibit proteases through their hydroxyl groups, because of an enhanced reactivity of its thiol ester.Proteins in the α-macroglobulin (αM) superfamily use thiol esters to form covalent conjugation products upon their proteolytic activation. αM protease inhibitors use theirs to conjugate proteases and preferentially react with primary amines (<i>e.g.</i> on lysine side chains), whereas those of αM complement components C3 and C4B have an increased hydroxyl reactivity that is conveyed by a conserved histidine residue and allows conjugation to cell surface glycans. Human α₂-macroglobulin-like protein 1 (A2ML1) is a monomeric protease inhibitor but has the hydroxyl reactivity-conveying histidine residue. Here, we have investigated the role of hydroxyl reactivity in a protease inhibitor by comparing recombinant WT A2ML1 and the A2ML1 H1084N mutant in which this histidine is removed. 2020-01-01T00:00:00Z2020 Dec2026-05-01T16:28:01.299Z2022-02-10T15:48:31.536ZS-EPMC78640683297826010.1074/jbc.RA120.015694