Structures inside living cells are often built from numerous copies of one protein. Like a brick wall made from many individual bricks, an oligomer can have size and strength unattainable by individual proteins. For example, during bacterial growth and division, a cell is pinched into two daughter cells by the action of a protein called FtsZ, many copies of which assemble into a ring that can constrict. In another example, when cells are stressed they respond by halting cellular activity. To do this they create a "mesh" of protein from many copies of TIA-1, which stalls protein synthesis by trapping mRNA in the "mesh". Oligomeric structures can be exquisitely sensitive to events in the cell, much more than an individual protein could be, as illustrated by the classic example of oligomeric hemoglobin which is much more sensitive to oxygen than a single hemoglobin protein. Although oligomeric structures are crucially important, little is known about how the protein molecules pack together to form the larger structures. It is expected that knowledge of the oligomeric structures gained through this project will enhance our understanding of the biological role of these proteins in the cell. This project will have broad impact through mentorship, teaching and outreach. The investigator has a strong record of mentoring women in science and these efforts will continue. Research activities will be showcased through outreach activities for middle and high school students.
Although our knowledge of protein structure has advanced considerably over the past 50 years, oligomeric proteins specifically have lagged behind, because they are difficult to study using traditional structural methods. This project pursues oligomeric structures through technical developments in solid state NMR, a promising new method that is well suited for determining structures of oligomeric proteins. In these studies, the signal strength is enhanced through the use of low temperatures and by transfer of signal from electron spin to nuclear spin, in a method called Dynamic Nuclear Polarization. Optimization of sample freezing protocols, and multidimensional detection schemes pursued in this project are expected to improve the low temperature linewidths and enable the process of determining structures. Although most studies will be carried out with in vitro samples, additional methods are developed for elucidating structures within living cells. The strategy for detection within the cell is to selectively enhance signals for the oligomeric protein of interest using a combination of selective isotopic enrichment and selective transfer of polarization from radicals tagged onto the protein of interest.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
