New insight into the mechanisms of collagen secretion
13 June 2016
A new paper from the Stephens lab providing some new insight into the mechanism of collagen secretion has been published in Cell Reports.
Collagen is the most abundant protein in the body. Fibril forming collagens, including collagen I, are made as large, 300 nm long precursors in the endoplasmic reticulum (ER), which and are then transported through the cell using the classical vesicular transport machinery. The first step in this pathway is the packaging into vesicles by the COPII coat, a complex of proteins that assemble at specific sites on the ER called ER exit sites. The COPII machinery is well described but classically generates 60-90 nm size vesicles that are too small to capture and transport large fibrillar collagens. A protein called TFG, known for its role at ER exit sites through interactions with COPII. The new work from the Stephens lab in the School of Biochemistry shows that TFG has a role in organizing ER exit sites into larger structures and that it has a key role in the secretion of collagens. A combination of imaging techniques, including super-resolution microscopy was used to show that on depleting cells of TFG, ER exit sites become more dispersed yet remain functional for the transport of small cargo such as Golgi membrane proteins. However, proteomics and cell imaging revealed a defect in the transport and secretion of extracellular matrix components including collagens. This work suggests a link between ER exit site organization and procollagen secretion that the lab are keen to follow up in the near future.
The work was conducted primarily by a MRC-funded postdoc, Vicky Miller, and a Masters student Janine McCaughey. Janine undertook this work as a part of her Master’s degree at the Leibniz University Hannover during a 6-month placement in the Stephens lab. Current postdoc Nikki Stevenson, as well as former lab members Anna Brown, and Annika Budnik contributed to the work. Key to the success of the project were the outstanding resources and support available within the Wolfson Bioimaging Facility (notably Dom Alibhai who wrote dedicated computer code for image analysis) and Proteomics Facility (where Facility Director Kate Heesom was key to the success of the project).
This work was funded by the Medical Research Council UK (grant numbers MR/J000604/1, MR/K018019/1, and G0801848). The Wolfson Bioimaging Facility has been funded generously by the Wolfson Foundation and University of Bristol; this work also benefited from additional equipment funded by the BBSRC (through BrisSynBio, a BBSRC/EPSRC-funded Synthetic Biology Research Centre: grant number: L01386X) and ALERT 13 capital grant (BB/L014181/1).
McCaughey et al., TFG Promotes Organization of Transitional ER and Efficient Collagen Secretion, Cell Reports (2016), http://dx.doi.org/10.1016/j.celrep.2016.04.062