Functional implications of MIR domains in protein O-mannosylation.

ABSTRACT: Protein O-mannosyltransferases (PMTs) represent a conserved family of multispanning endoplasmic reticulum membrane proteins involved in glycosylation of S/T-rich protein substrates and unfolded proteins. PMTs work as dimers and contain a luminal MIR domain with a ?-trefoil fold, which is susceptive for missense mutations causing ?-dystroglycanopathies in humans. Here, we analyze PMT-MIR domains by an integrated structural biology approach using X-ray crystallography and NMR spectroscopy and evaluate their role in PMT function in vivo. We determine Pmt2- and Pmt3-MIR domain structures and identify two conserved mannose-binding sites, which are consistent with general ?-trefoil carbohydrate-binding sites (?, ?), and also a unique PMT2-subfamily exposed FKR motif. We show that conserved residues in site ? influence enzyme processivity of the Pmt1-Pmt2 heterodimer in vivo. Integration of the data into the context of a Pmt1-Pmt2 structure and comparison with homologous ?-trefoil - carbohydrate complexes allows for a functional description of MIR domains in protein O-mannosylation.

SUBMITTER: Chiapparino A 

PROVIDER: S-EPMC7759382 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature