Thioester protein crosslinks

Thioester bonds between cysteine and glutamine sidechains can form covalent cross-links between polypeptide chains. Thioester bonds are one way that ubiquitin may be attached to proteins (ubiquitinylation). Thioester bonds in complement proteins C3 and C4 are involved in tagging pathogens for destruction by the immune system, via the alternate complement activation pathway. Thioester bonds occur in thioester domains (TED) of Gram-positive bacteria, where they are thought to mediate covalent adhesion of bacteria to host cells.