Structure, sequon recognition and mechanism of tryptophan C-mannosyltransferase

Abstract

C-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 Caenorhabditiselegans 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.

Conservation, abundance, glycosylation profile, and localization of the TSP protein family in Cryptosporidium parvum

“…Given the preponderance of tryptophan C-mannosylation sites on the Cp TSP protein family, it seems likely that this protein modification will be important to several aspects of the parasite’s life cycle, and that the dpy-19 enzyme that installs this protein modification may have potential as a novel drug target. Indeed, apicomplexan dpy-19 enzymes are among the most divergent from mammalian homologs, and structural data for this enzyme family are now available ( 54 ), suggesting that it may be possible to develop selective inhibitors of the C. parvum dpy-19 homolog. Furthermore, the molecular genetic techniques needed to validate this potential drug target are now available ( 55 ).…”

Friedel–Crafts reactions for biomolecular chemistry

“…S3, ESI †). 54 A metabolite with electron-rich benzene rings and chloroalkanes is known to cause an enzymatic homo-dimerization process, generating a cytotoxin in cyanobacteria (Scheme 3B). Cylindrocyclophane derivatives are cytotoxins, and their biological importance is increasingly studied.…”

Promiscuous Enzymes for Residue‐Specific Peptide and Protein Late‐Stage Functionalization

“…It catalyzes the C−C bond formation by transferring mannose from the dolichylphosphate mannose to the C2 indole position of first Trp in a WxxW/C sequon in proteins and peptides (Figure 10). Structural data of DPY‐19 indicate that the mechanism of C ‐glucosylation proceeds through electrophilic aromatic substitution and that Glu71 seems to act as the catalytic base [215] …”