Research
The Golgi: linking vesicular sorting with glycan processing
In our research we focus on the function of the Golgi apparatus. This organelle was named after the Italian physician Camillo Golgi, whose revolutionary staining technique allowed for its visualization. Since Golgi's discovery the work of many scientists allowed deeper insight into the two main functions of this secretory organelle - the sorting and the modification of proteins destined to locations in and outside the cell. We are aiming for a synthesis of the Golgi's functions in our research. The three areas detailed below are asking:
1. What can we learn about the molecular mechanism of sorting within the Golgi?
2. How sorting influences glycan biosynthesis?
3. What are the physiological roles of protein glycosylation?
EM image of the Golgi in CHO cells
The molecular mechanism of sorting
Protein transport within the Golgi, as everywhere else in the cell, is a two-way business. Forward transport carries proteins through the Golgi cisternae until they reach the Trans-Golgi Network (TGN), from where they are sorted to endosomes, lysosomes or the plasma membrane. These proteins have to be distinguished from the resident Golgi proteins, which do not leave the Golgi but cycle within it. This cycling is carried out by small vesicles that travel backwards through the Golgi. Our focus is on the targeting of these vesicles to their correct location. This event is called vesicle tethering. Our research in this area focuses on the vesicle tethering reactions guided by the COG vesicle tethering complex. We are characterizing some already known and several novel interactions between COG and other proteins of the Rab, golgin and SNARE families.
Enzyme sorting and glycan biosynthesis
It is clear that the correct localisation of glycosylation enzymes in the Golgi is necessary for the faithful synthesis of oligosaccharides, also called glycans, onto proteins. It is much less well known how the regulation of the localisation machinery, including that of the vesicle targeting machinery, is expoited to engineer glycans for diverse physiological roles or during pathologies. Our goal is to uncover this link by investigating how the enzymes are sorted to their specifc locations throught the action of vesicle tethering. At the same time we are looking at the regulation of the tethering proteins to link this with the targeting information.
The physiological role of protein linked glycans
The glycans linked to proteins are clearly important in their own right, not just as a supporting/modifying role for their proteins. However, it has been very difficult to pin down what these roles are, because traditional genetic and biochemical techniques mostly fail due to the complexity and the inherent heterogeneity of glycans. We are approaching this problem through a 'forward glycomics' approach by perturbing glycosylation through changes to Golgi organization, observing phenotypes and then investigating which glycan chains are responsible for the observed changes. We heavily rely on collaborators for this, and have started looking at stem cell differentiation and fly tissue development.
Glycan biosynthesis using computational modelling
Part of the research that is carried out in the Ungar lab is computational in nature. Using a computational model we hope to unravel the link between glycosylation machinery and glycan biosynthesis; with larger aims to make better biologics.
The computational model is underpinned by two different methodologies: stochastic simulation and approximate Bayesian computation. Carefully woven together this method allows us to use our prior knowledge of the system and make rational predictions as to how glycosylation needs to change in order to generate specific glycans. More can be read here.
