Grant: Discovery Grants Program - Individual

The plasma membrane is the barrier between the inside of a cell and its environment. These membranes are often described as "seas" of free-floating lipids with protein "icebergs" that freely diffuse (move) through the "sea". In reality, membranes are divided into small regions, with movement between regions restricted by membrane-embedded structures. These diffusion-restricting structures divide membranes into small regions that take on specialized functions, and there are multiple types of these structures that control diffusion over different size and time scales. We are interested in two of these structures - corrals and cages, with the goal of better understanding the composition and dynamics of these structures, and using this information, develop a model of protein diffusion that accounts for the effects of cages and corrals. Corrals are "picket-fences" created by "picket" proteins that are attached to the cells "skeleton", and extend through the membrane to create a "percolation barrier" that limits egress from the corral. Our recent work determined that corrals may selectively trap old proteins, which are then endocytosed (internalized) to remove them from the membrane. Cages - recently discovered by my NSERC research program - are more mysterious. Their composition and role are unknown, but they act like corrals over shorter periods of time. We have tentatively identified the protein spectrin as a structural component of cages, and developed the tools needed to directly image cages and corrals in the cell membrane. In aim 1 we will identify and characterize the proteins which form cages. In aim 2 we will address whether corrals selectively remove older proteins from the plasma membrane, and whether the release (exocytosis) of new proteins clears the surrounding membrane of corrals. Lastly, we will continue our development of a mathematical model of protein diffusion in the cell membrane, as current models do not account for the role of cages and corrals. We have shown that the Continuous Time Random Walk model best describes the effect of corrals and cages on the diffusion of one protein; in aim 3 we will use a panel of proteins representing the major structure classes of membrane proteins to determine whether this model is a general model of protein diffusion. In the long-term this program will uncover the processes used to organize proteins on the cell surface, and in the short-term it will identify the key structuring mechanisms and their composition. The HQP trained by this program gain experience in microscopy and computer-aided analyses, with previous HQP using this expertise to launch careers developing the next generation of software for diagnosing diseases in MRI imaging and in histological samples. This program will continue my successful training of HQP in advanced forms of microscopy and image analysis, providing these trainees with skills which are highly in-demand in the microscopy and image processing industries.