Protein secretion is conducted by the ubiquitous Sec-complex. In bacteria the SecYEG protein-channel complex delivers proteins across the plasma membrane, whereas the eukaryotic Sec61-complex does so into the ER-lumen. We understand the bacterial process best, due to the availability of high-resolution structures. Unfortunately, more complex aspects of the eukaryotic system cannot be addressed in the bacterial model. Translocation through the ER membrane turns out to be regulated by additional factors in the cytosol, ER lumen and by calcium. Moreover, Sec61 also interacts with specialised components responsible for membrane insertion, protein degradation and protein glycosylation. The project aims to elucidate the structure of the eukaryotic system in order to help understand these diverse properties.
In general membrane protein structures are highly conserved in the positioning of the trans-membrane segments (TMS) and more divergent in the connecting loops. This is evident in the Sec-complex, reflecting the distinct interactions at the ER and bacterial inner membranes. Rather than determining the Sec61 structure from scratch, the project will carry out a more feasible reconstruction. The existing SecYEG-complex will be used as a basis for the location of the TMSs. The connecting loops will be engineered and produce for structure determination by NMR. The structures will then be spliced onto the structure of the membrane sector. The working Sec61 model will then be refined by energy minimisation and molecular dynamics simulations and the final structure will be verified in vivo in tests exploiting the genetically tractable eukaryote Saccharomyces cerevisiae.
Webpage: http://www.bch.bris.ac.uk/staff/ic.html
Funding Notes:
Competitive funding for UK/EU students via the BBSRC SWDTP is currently available as follows:
Structure and function of the eukaryotic Sec61-translocon - Dr Collinson, Dr Sessions, Dr Crump.
For an opportunity to undertake a SWDTP funded project with this supervisor, please visit the SWDTP website:
http://www.bristol.ac.uk/swdtp
When applying online, please ensure you include "SWDTP Funded Project" in the "Research Details" section of the online form.
References:
Hizlan, D., Robson, A., Whitehouse, S., Gold, V. A., Vonck, J., Mills, D., Kühlbrandt, W., et al. (2012). Structure of the SecY Complex Unlocked by a Preprotein Mimic. Cell reports, 1(1), 21–28. doi:10.1016/j.celrep.2011.11.003
Van den Berg, B., Clemons, W. M., Collinson, I., Modis, Y., Hartmann, E., Harrison, S. C., & Rapoport, T. A. (2004). X-ray structure of a protein-conducting channel. Nature, 427(6969), 36–44. doi:10.1038/nature02218
Breyton, C., Haase, W., Rapoport, T. A., Kühlbrandt, W., & Collinson, I. (2002). Three-dimensional structure of the bacterial protein-translocation complex SecYEG. Nature, 418(6898), 662–665. doi:10.1038/nature00827