Membrane protein misfolding and disease: quality control pathways

Misfolded proteins represent a continuous threat to cell viability, and if allowed to accumulate, can disrupt cellular function and induce cell death. Therefore, cells possess quality control systems in order to detect and destroy abnormally folded polypeptides. 20-30% of all human proteins are predicted to be integral membrane proteins, which have one or more hydrophobic membrane spanning domains that anchor the protein into the lipid bilayer. The biosynthesis of membrane proteins is a complex process and perhaps unsurprisingly, many human diseases are linked to the misfolding of membrane proteins (Ng et al., 2012). Therefore, there is great interest in understanding the quality control processes that identify and remove misfolded membrane proteins from human cells.

Over the past 15 years, much has been learned about how protein folding in the cytoplasm and the lumen of the endoplasmic reticulum is monitored (Christianson and Ye, 2014). However, little is currently known about how defective membrane spanning domains are recognised. We have recently found that quality control checkpoints at the endoplasmic reticulum (Briant et al., 2015), Golgi apparatus and plasma membrane are able to recognise a simple model protein containing a defective transmembrane domain.

The aim of this project is to further define these quality control pathways using the peripheral myelin membrane protein PMP22. Missense mutations in PMP22 cause peripheral neuropathies including Charcot-Marie-Tooth (CMT) disease, and several of the disease-causing mutations are known to disrupt the proper arrangement of transmembrane domains (Schlebach et al., 2015), making PMP22 an attractive model for these studies. The results of this work will lead to greater understanding of the molecular mechanisms that maintain the quality of the membrane proteome, and also provide new insight into the molecular basis of PMP22 related diseases.

A range of cell biology, biochemistry, molecular biology, bioimaging and proteomic methods will be utilised, including mammalian cell culture, generation of stable cell lines, expression of disease-associated mutant proteins, siRNA knockdown, immunofluorescence microscopy, SDS-PAGE and western blotting, immunoprecipitation, mass spectrometry, molecular cloning and site directed mutagenesis.

Candidates are expected to hold (or be about to obtain) a minimum upper second class honours degree (or equivalent) in a related area such as Biochemistry, Cell Biology, Biomedical Sciences, Neurosciences.