The E3 ligase HOIL-1 catalyses ester bond formation between ubiquitin and components of the Myddosome in mammalian cells

The formation of isopeptide bonds between the C-terminal carboxylate of ubiquitin and ε-amino groups of lysine residues on another protein is a major mechanism for regulating protein function. Ubiquitin can also form peptide bonds with the N-terminal α-amino group of another ubiquitin, a reaction catalysed by the HOIP component of the linear ubiquitin assembly complex (LUBAC). Here, we identify the HOIL-1 component of LUBAC as an unusual ligase that catalyses the formation of oxyester bonds between the C-terminal carboxylate of ubiquitin and serine and threonine residues in other proteins. We identify components of the Myddosome as physiological substrates of HOIL-1, indicating a role for HOIL-1 in regulating innate immunity.