Oral Presentation 23rd Annual Lorne Proteomics Symposium 2018

Whoa man! Unexpected protein O-mannosylation pathways (#45)

Henrik Clausen 1 , Ida Signe Bohse Larsen 1 , Yoshiki Narimatsu 1 , Hiren Jitendra Joshi 1 , Sergey Y. Vakhrushev 1 , Adnan Halim 1
  1. Copenhagen Center for Glycomics, Depart. of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

Until recently protein O-Mannosylation in yeast and metazoans was thought to be directed by a single family of conserved orthologous protein O-Mannosyltransferases (pmts/POMTs). The family of pmts is essential in yeast, and in humans the orthologous POMTs underlie a subgroup of congenital muscular dystrophies designated α-dystroglycanopathies that are caused by loss of O-Mannosylation of a-dystroglycan. Recently, novel types of O-mannosylation in yeast and in metazoans were discovered using gene engineering and lectin-enriched O-Mannose glycoproteomics, and it appears there may be more to come. Analysis of the yeast O-Mannose glycoproteome pointed to a novel nucleocytoplasmic type of O-mannosylation resembling the nucleocytoplasmic O-GlcNAcylation found in eukaryotic cells except yeast1, 2, although the yeast enzyme(s) responsible for the O-mannosylation is still unknown. In higher eukaryotes O-mannosylation of cadherins was found to be independent of the POMTs3, 4, and using a CRISPR/Cas9 genetic dissection strategy combined with sensitive and quantitative O-Man glycoproteomics, we identified a novel family of TMTCs encoded O-Mannosyltransferases5. Congenital deficiency in the TMTC3 gene was shown to underlie Cobblestone Lissencephaly with brain malformation. The TMTC1-4 genes were imperative for cadherin and protocadherin O-Man glycosylation, and using combinatorial knockout of TMTC1-4 distinct roles of the individual isoenzymes for specific b-strands of the cadherin EC domains were identified. In addition, O-Man glycosylation of IPT/TIG domains of Plexins and hepatocyte growth factor receptor (HGFR) was not affected in TMTC KO cells, suggesting the existence of yet another O-Man glycosylation machinery. Our study demonstrates that regulation of O-mannosylation in higher eukaryotes is much more complex than envisioned.

  1. Neubert, P. et al. Mapping the O-Mannose Glycoproteome in Saccharomyces cerevisiae. Molec Cell Prot 15, 1323-1337 (2016).
  2. Halim, A. et al. Discovery of a nucleocytoplasmic O-mannose glycoproteome in yeast. Proc Natl Acad Sci USA 112, 15648-15653 (2015).
  3. Vester-Christensen, M.B. et al. Mining the O-mannose glycoproteome reveals cadherins as major O-mannosylated glycoproteins. Proc Natl Acad Sci USA 110, 21018-21023 (2013).
  4. Larsen, I.S.B. et al. Mammalian O-mannosylation of cadherins and plexins is independent of protein O-mannosyltransferases 1 and 2. J Biol Chem 292, 11586-11598 (2017).
  5. Larsen, I.S.B. et al. Discovery of an O-mannosylation pathway selectively serving cadherins and protocadherins. Proc Natl Acad Sci USA 114, 11163-11168 (2017).