Institute for Molecular Biosciences, The University of Queensland
Retromer is a multi-subunit protein complex with important roles in the retrograde transport of transmembrane receptors from endosome to the trans-Golgi network (TGN). Precise sorting of these cargo proteins to different destinations requires proper formation of multiple endosome-transport carries (ETCs), which is spatially and temporally coordinated by retromer. Retromer dysfunction results in the defects on endosome transport, and is often linked to multiple neurodegenerative disorders, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). Mammalian retromer comprises a trimer complex composed of three subunits Vps35, Vps26 and Vps29 for cargo recognization, and a sorting nexin dimer composed of SNX-BAR proteins for driving tubule formation and recruiting cargoes to endosomes. Once ETCs formed, Golgi-associated protein family, termed “Golgins”, tethers and transports these vesicles to the cytoplasmic face of the Golgi. Exploiting individual Golgin proteins engineered to target these proteins to the mitochondria we have examined which ETCs depend on retromer-modulated retrograde trafficking pathway. We find Golgins, including GCC88, golgin-97 and golgin-245 all can recruit CI-M6PR to the mitochondria-positive structures. The tethering of CI-M6PR to the mitochondria by GCC88 is impaired by retromer Vps35 knockout. We are currently investigating if PD-associated retromer mutants, which has been shown to have impact on CI-M6PR trafficking, directly impact on the formation of these ETC’s. In summary, this new assay will allow for the quantification of individual retromer dependent cargo sorting into the distinct types of ETCs.