Chemistry 2008
Area of Doctoral Study: Chemistry
Undergraduate Institute: Hood College
Research Advisor: Colin Garvie, Ph.D., Michael F. Summers, Ph.D.
Current Position : Director, Center for Strategic Philanthropy, Milken Institute
Description of Research
MHC II molecules are transmembrane heterodimeric glycoproteins that play a key role in the immune response cascade. MHC II molecules are expressed exclusively in antigen presenting cells (APC). The primary function of APCs are to ingest, process, and present protein antigens to T-cells to initiate humoral immune response. In this process antigens enter APCs via phagocytosis or endocytosis. Once in the cell they are proteolyzed by endosomes and subsequently bound by MHC II molecules. MHC II transports the antigenic peptide to the surface of the APC, where the peptide MHC II complex fuses to the receptors on CD4+ T-cells, initiating immune response to eliminate the antigen. Expression of MHC II molecules is regulated by a trans-acting multi-protein complex called the MHCII enhanceosome. The MHCII enhanceosome is comprised of four proteins RFX, NFY, CREB, and CIITA. RFX, NFY, and CREB are found in all somatic cells, however the interaction of these three proteins alone does not induce expression of MHC II. The transactivator protein, CIITA completes the enhanceosome and stimulates transcription of MHC II genes. CIITA is exclusively expressed in APCs, however expression can be induced with cytokines such as interferon gamma. Other key features of CIITA include its ability to interact with RNA polymerase and chromatin machinery, and its intrinsic histone acetyl transferase (HAT) activity. Critical mutations and deletions in the RFX complex or CIITA prevents expression of MHCII. MHC II deficiency causes Bare Lymphocyte Syndrome (BLS), a recessive autosomal disease. Patients that suffer from this disease have severely suppressed immune systems, and often do not survive beyond adolescence. The aim of our laboratory is to explore the structure and behavior of each of the enhanceosome proteins to elucidate how these transcription factors come together to initiate transcription of MHCII genes. By solving this problem we will be able to identify potential targets for immunosuppressive drugs. Such targets are of importance because they will allow the medical community to combat autoimmune disorders, and hyperactive immunity resulting from transplant rejection. My research focuses on the RFX complex. The three subunits of RFX are RFXB, RFX5, and RFXAP. The aim of my research is to express and purify full length and truncated fragments of the RFX proteins in order to conduct the following experiments: 1) investigate the interaction between the three RFX proteins in solution by determining the relevant association constants using isothermal titration calorimetry, 2) Determine the oligomeric state of the RFX proteins alone and in the binary and ternary complexes using static light scattering and crosslinking methods, 3) Solve the structure of the individual proteins, their binary complexes and the full RFX ternary complex using X-ray crystallography.