A key component of the implementation of an organism’s genome is the correct deployment of every gene product. This is particularly true of eukaryotic cells, which possess distinct compartmentalization that segregates biochemical functions of the cell. Fully one third of the eukaryotic proteome transits through the secretory pathway and therefore must enter the endoplasmic reticulum (ER), which serves as the gateway to this endomembrane system. The ER is charged with many duties, including promoting protein folding, ensuring protein quality control and initiating the process of protein trafficking for delivery to downstream compartments. Egress from the ER is mediated by transport vesicles that are sculpted from the donor membrane through the coordinated action of a set of cytoplasmic “coat” proteins, known as the COPII coat (Fig. 1). This coat complex simultaneously deforms the membrane into small spherical structures and populates the nascent vesicles with cargo proteins that are destined for forward traffic.
Research
Fig 1. Assembly of the COPII coat. The small G-protein, Sar1p, initiates coat recruitment through the action of the GEF, Sec12p. The Sec23p/Sec24p dimer binds and selects cargo proteins into the nascent bud; adjacent pre-budding complexes are gathered by the Sec13p/Sec31p heterotetramer, which completes vesicle formation to yield a 60-80nm vesicle (right panel). From Lee et al. (2004) Ann Rev Cell Dev Biol.
Research in the Miller lab is broadly aimed at understanding the rules that govern uptake of cargo proteins into nascent vesicles, a process that is influenced by the presentation of sorting signals, by the folding state of the client protein and by the coat itself. We use the budding yeast, Saccharomyces cerevisiae, as a model system, which affords a vast array of biochemical, genetic, genomic and proteomic tools that can be brought to bear on this fundamental biological problem. Three main research arms of the Miller lab attack this problem from different angles: