Investigating the function of the hereditary spastic paraplegia protein spastin in the endomembrane system

Hereditary spastic paraplegias (HSPs) are genetically inherited neurological diseases characterised by the distal axonal degeneration of corticospinal neurons. Of the 80 genes currently associated with HSP, mutations in SPAST, encoding the protein spastin, are by far the most common cause of pathology. Spastin functions as a microtubule remodelling enzyme by using energy derived from ATP hydrolysis by its ATPase domain. The location of this activity is governed by spastin’s localisation domains which mediate recruitment to membrane sites including endosomes and the ER. In this thesis I aimed to elucidate the function of spastin at these sites, as well as to analyse the resulting effects on the cell surface proteome. Through this work, I have shown that spastin functions to mediate the fission of endosomal recycling tubule and have confirmed spastin’s localisation to ER exit sites, but show using synchronised secretion assays that spastin is dispensable for generalised cargo secretion of at least 2 classes of secretory cargo. Finally, through quantitative cell surface proteomics, I show that mutation of spastin’s ATPase domain induces substantial remodelling of the cell surface proteome, and through this have generated a list of pathological candidates whose change in surface abundance could drive the pathogenicity of spastin-HSP.Medical Research Council PhD Studentship Cambridge Institute of Medical Researc