Bloch, Joël SJoël SBlochJohn, AlanAlanJohnMao, RunyuRunyuMaoMukherjee, SomnathSomnathMukherjeeBoilevin, Jérémy MathiasJérémy MathiasBoilevinIrobalieva, Rossitza NRossitza NIrobalievaDarbre, TamisTamisDarbreScott, Nichollas ENichollas EScottReymond, Jean-LouisJean-LouisReymond0000-0003-2724-2942Kossiakoff, Anthony AAnthony AKossiakoffGoddard-Borger, Ethan DEthan DGoddard-BorgerLocher, Kaspar PKaspar PLocher2024-10-142024-10-142023-05https://boris-portal.unibe.ch/handle/20.500.12422/116958C-linked glycosylation is essential for the trafficking, folding and function of secretory and transmembrane proteins involved in cellular communication processes. The tryptophan C-mannosyltransferase (CMT) enzymes that install the modification attach a mannose to the first tryptophan of WxxW/C sequons in nascent polypeptide chains by an unknown mechanism. Here, we report cryogenic-electron microscopy structures of Caenorhabditis elegans CMT in four key states: apo, acceptor peptide-bound, donor-substrate analog-bound and as a trapped ternary complex with both peptide and a donor-substrate mimic bound. The structures indicate how the C-mannosylation sequon is recognized by this CMT and its paralogs, and how sequon binding triggers conformational activation of the donor substrate: a process relevant to all glycosyltransferase C superfamily enzymes. Our structural data further indicate that the CMTs adopt an unprecedented electrophilic aromatic substitution mechanism to enable the C-glycosylation of proteins. These results afford opportunities for understanding human disease and therapeutic targeting of specific CMT paralogs.en500 - Science::570 - Life sciences; biology500 - Science::540 - Chemistry600 - Technology::610 - Medicine & healtharticle10.48350/1769413660456410.1038/s41589-022-01219-9