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Strahl labOur Projects

The principles of O-mannosylation and its interplay with N-glycosylation

Protein O-mannosylation and N-glycosylation are fundamental processes that are essential for the growth and development of eukaryotes. Both protein modifications initiate at the endoplasmic reticulum. Properly glycosylated and folded proteins can journey on to the Golgi apparatus where N-linked and O-mannosyl glycans are further trimmed and/or elongated. Ultimately, glycoproteins with highly diverse glycans emerge. The importance of these protein modifications becomes obvious in light of the fact that defects in both types of glycosylation result in severe human diseases such as the congenital disorders of glycosylation (CDGs).

In the endoplasmic reticulum, the N-glycosylation machinery and protein O-mannosyltransferases compete for the sugar donor dolichol phosphate-activated mannose. There is now growing evidence that the connection between O-mannosylation and N-glycosylation extends far beyond their sharing of a common sugar donor (reviewed in Neubert and Strahl, 2016). Our recent work revealed that the inhibition of mammalian protein O-mannosyltransferases affects Cadherin-mediated cell-cell adhesion, via unexpected crosstalk between O-mannosylation and the biosynthesis of individual N-glycan structures on this important adhesion molecule (Lommel et al., 2013; Carvalho et al., 2016; Noor et al., 2021). It is still unclear, however, whether the observed effects are restricted to Cadherins or whether N-glycosylation is generally affected by a decrease in O-mannosylation, and what mechanisms are behind this coordinated interplay.

To address these questions, we aim to study mammalian O-mannosylation and its relation to N-glycosylation at the operating, regulatory and functional levels.

Our main objectives are

  1. unravel the mode of action of the eukaryotic PMT-family O-mannosyltransferases in the endoplasmic reticulum (Shahidul Alam, Anke Metschies)
  2. explain the consequences of defective O-mannosylation at the molecular level with a focus cell adhesion molecules (Sina Noor)
  3. study the interplay of O-mannosylation and N-glycosylation in CDG models (Daniel Sturm)

In combination, our analyses will provide a comprehensive view of the initiation of O-mannosylation in the endoplasmic reticulum as well as the diverse implications of O-mannosylation defects, and guide the analyses of physio-pathologic abnormalities in CDG models.


Structural and functional characterization of the O-mannosyl glycans

 Protein O-mannosylation is conserved from yeast to humans and defines a new pathomechanism of neuromuscular diseases. We established an MS-based workflow and specific tools for the detection of O-mannosyl glycans that resulted in the identification of cadherins as mono-O-mannosylated proteins. We continue to screen for novel substrates of O-mannosylation and to study the impact of these glycans on the performance of the carrier proteins. Having established the first O-mannose glycoproteome (Neubert et al., 2016), we now take further advantage of proteomics and glycoproteomics as well as other high throughput screening approaches to decipher the role of O-mannosylation for the performance of its target proteins in baker's yeast.
People involved: Anke Metschies