Prof. Dr. Sabine Strahl
1) The principles of O-mannosylation and its interplay with N-glycosylation
Protein translocation in the endoplasmic reticulum (ER) and protein glycosylation are intimately connected, fundamental processes essential for the normal functioning of eukaryotic cells. Nascent polypeptide chains of secretory and membrane proteins are N-glycosylated and O-mannosylated while they are translocated across the ER membrane. The translocation and concurrent N-glycosylation of these proteins take place on a large molecular machine, the translocon complex (TC), which is associated with membrane-bound polysomes. We demonstrated that in Saccharomyces cerevisiae Pmt1-Pmt2 complexes associate with the Sec61 translocon as well as oligosaccharyltransferase. We established a cell free translation/translocation/glycosylation system which now allows us to unravel the molecular basis of coupling protein translocation and N-glycosylation with protein O-mannosylation. In the framework of FOR2509 we extend our studies to mammalian systems.
People involved: Ewa Zatorska, Sina Ibne Noor, Ricardo Carvalho, Christina Hölscher
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, 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: Sina Ibne Noor, Patrick Neubert, Anke Metschies
In all eukaryotes the proper folding and maturation of proteins in the endoplasmic reticulum (ER) is both aided and monitored by a number of chaperones and folding enzymes in a complex process referred to as ER quality control (QC). ER-QC is compromised under a variety of conditions, collectively termed ER stress, which cause the accumulation of misfolded proteins in the ER lumen. Eukaryotic cells cope with ER stress by activating a multi-layered protective response, the unfolded protein response (UPR), which adapts the secretory pathway to the ER protein load and increases the efficiency of protein folding. In fungi and animals, O-mannosylation is an essential protein modification that is initiated in the ER by a conserved family of protein O-mannosyltransferases (PMTs). It was recently observed that O-mannosylation of membrane and secretory proteins is especially crucial during ER stress; however, molecular functions and mechanisms are poorly understood.
In the framework of the SFB1036 we want to dissect the role of protein O-mannosylation with respect to ER homeostasis during stress conditions.
People involved: Joan Castells-Ballester, Patrick Neubert, Anke Metschies