1. Different ubiquitin linkage types and their role in immune signallingUbiquitin, a small protein of 76 amino acids, can be attached to a substrate protein or to a ubiquitin molecule that is already attached to a substrate, with the latter resulting in an inter‐ubiquitin linkage.
Different ubiquitin linkage types and their role in immune signallingUbiquitin, a small protein of 76 amino acids, can be attached to a substrate protein or to a ubiquitin molecule that is already attached to a substrate, with the latter resulting in an inter‐ubiquitin linkage. Attachment to substrates will typically occur through an isopeptide bond between the ε‐amino group of a lysine residue (K) within the substrate protein and the C‐terminal carboxyl group of glycine 76 (G76) of ubiquitin. Inter‐ubiquitin linkages are usually between the ε‐amino group of one of the seven internal lysine residues (K6, K11, K27, K29, K33, K48 and K63) of the substrate‐associated acceptor ubiquitin and the carboxyl group of G76 of the incoming ubiquitin2. Another type of inter‐ubiquitin linkage can be formed between the α‐amino group of the N‐terminal methionine 1 (M1) of the substrate‐associated ubiquitin and the carboxyl group of G76 of the incoming ubiquitin. The resulting linkage type is called M1‐ or linear linkage. Different inter‐ubiquitin linkage types fulfil different functions in immune signalling. The functions currently attributed to the different linkage types are summarised in the respective boxes. Removal of ubiquitin is carried out by DUBs, which have recently been shown to specifically cleave certain linkage types, for example CYLD cleaves K63‐ and M1–linkages.
Julia Zinngrebe et al. EMBO Rep. 2014;15:28-45
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