The structure and function of SGTA, a key regulator of protein quality control

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I am well placed to accede the overwhelming focus of protein targeting to the ER has been the fidelity and elegance of signal recognition particle dependent delivery. In contrast, efficiency was not a major concern, and hence the idea that a significant proportion of proteins destined for the ER can mislocalise to the mammalian cytosol is new. Nevertheless, the evidence for, and importance of, mislocalised proteins (MLPs) are now compelling, and a key component of the cellular pathway that deals with them is the focus of this project. MLPs are membrane and secretory protein precursors that fail to reach their intended destination and default to the cytosol. It is now apparent that MLPs are dealt with by a specific branch of the global cellular quality control network, and that SGTA plays a pivotal role in dictating their fate. SGTA acts in tandem with a second component, the BAG6 complex, forming a cycle: SGTA directs its MLP substrates towards deubiquitination and hence stabilisation; BAG6 directs them towards polyubiquitination and proteasomal degradation. Key to this pivotal role of SGTA is its capacity to recognise and bind to MLPs, yet we know little about the nature or extent of its substrate-binding region and have no detailed structural information whatsoever. Likewise the functional role of its novel N-terminal interaction motif is completely unexplored. Our major goals are therefore to obtain a complete molecular understanding of the interaction between SGTA and membrane proteins, and to define the importance of its UBL- and substrate- binding domains to the cellular quality control of MLPs. These studies will build on our recent successful studies of SGTA structure and function, and exploit a range of established tools, reagents and validated model MLPs, combined with robust in vitro and in vivo functional readouts.

Protein secretion is a fundamental cellular process that is relevant in a number of spheres including biology, industry and medicine. The early stages of secretory protein production are intimately linked to the function of the endoplasmic reticulum, and our goal is to define the molecular basis of a novel pathway for the entry of proteins into the mammalian secretory pathway. The most direct economic impact of this work will be on the use of cultured mammalian cells for the production of high-value therapeutic proteins or biopharmaceuticals. The biological complexity of such components, combined with the physiological requirements of their targets, makes the use of mammalian cells the most viable platform for their production. The high cost and modest yields of such systems means that companies like Novo Nordisk have a substantial interest in trying to exploit current and emerging basic knowledge in order to enhance and improve output. Such approaches include strategies to enhance the early stages of secretory protein biogenesis at the endoplasmic reticulum by the rational engineering of cell line, and our work is directly relevant to these aspirations. In addition, there is anecdotal evidence that "premature" quality control may also reduce the yields of selected biopharmaceuticals, and our work addresses this issue directly. Pharmaceutical companies, including Novartis, have previously developed small molecules that directly inhibit the translocation of selected secretory proteins into the endoplasmic reticulum and explored their use as potential therapeutics. The outcomes of this project will provide the basis for complementary approaches that selectively inhibit the production of short secretory proteins. Our membership of the research council funded Manchester Chemical Biology Network gives us informal access to pharmaceutical companies (including AstraZeneca, GSK, Pfizer and Syngenta), providing a direct opportunity to explore and refine this strategy.

Both applicants are strongly committed to engaging with the general public about the importance of Science and the specific goals of their research. We actively participate in University and Faculty open days, and are proactive in our interactions with local schools. Hence, we have contributed to a variety of science-based activities in schools and provided mentoring to a nearby six-form college. We strongly encourage our staff and students to take part in raising the profile and understanding of science in the wider society, and in recent years our groups have participated in public events hosted by the University (Darwin Day at the Manchester Museum) and the Faculty of Life Sciences (Science Stars Days for Secondary School pupils).