Abstract
The endosomal network is a central sorting station for transmembrane proteins (cargoes) which enter from the cell surface or the biosynthetic pathway. Here, cargoes are subject to a major fate decision: degradation versus retrieval and recycling. For cargoes fated to be degraded, they are retained within the endosomal limiting membrane and sorted into intraluminal vesicles, where they will eventually be degraded once late endosomes fuse with the lysosomes. To be reused, cargoes are retrieved from this degradative fate and recycled to other cellular compartments, such as the plasma membrane or the trans-Golgi network.Retromer, a heterotrimeric complex of VPS35:VPS29:VPS26 (VPS26A and VPS26B are expressed in mammals), is the best-characterised endosome-localised cargo retrieval complex and is responsible for the retrieval of hundreds of different cargoes away from the degradative fate. The dysfunction of retromer has been implicated in diseases such as Alzheimer’s disease and Parkinson’s disease. To function correctly, retromer relies on its association with various proteins and multiprotein complexes. It is therefore not surprising that the most common Parkinson’s disease-causing variant of retromer, VPS35(p.D620N), exhibits a reduced association with one of its most significant interactors: the WASH complex.
In this thesis I investigated some of retromer’s interactions to gain insight into their functional significance. I firstly showed that retromer’s interaction with SNX3, a major retromer cargo adaptor, is vital for the establishment of Wnt morphogenic gradients. I also identified that SNX3-retromer couples to an evolutionary-conserved flippase complex to link cargo recognition with membrane deformation. Secondly, by investigating whether other Parkinsonism-associated retromer variants also exhibit reduced interactor associations, I showed that the VPS26A(p.K297X) variant causes a severe perturbation in retromer’s assembly with another cargo adaptor: SNX27. Finally, I identified that retromer couples to the WASH complex through a series of basic amino acids located on the carboxyl-terminus of VPS35 in proximity to the ASP620 residue. By creating retromer variants which have largely lost the ability to associate with the WASH complex, I showed that this interaction appears to be important for the segregation of the endosomal retrieval and degradative subdomains.
| Date of Award | 19 Mar 2019 |
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| Original language | English |
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| Supervisor | Pete J Cullen (Supervisor) |