Viral immunoevasins are key molecules employed by viruses to subvert the host immune response during infection. Understanding the molecular basis of their functions is key for explaining how viruses have adapted to specifically infect selected hosts and for the design of new vaccines and other antiviral therapies. Mouse cytomegalovirus (MCMV) has a set of such proteins that specifically interfere with major histocompatibility complex class I (MHC-I) antigen presentation to CD8+ T cells and natural killer (NK) cells. Notwithstanding the large number of genetic and functional studies, the structural biology of immunoevasin specificities and functions is poorly understood, due largely to bottlenecks in co-crystallizing these proteins and their ligands. To bypass this bottleneck I have developed a new approach that combines sparse datasets recorded from nuclear magnetic resonance (NMR) spectroscopy with sophisticated Rosetta modeling methods. This hybrid approach now permits accurate structure determination of protein complexes in the 30kD-50kD range, a size previously unapproachable by NMR techniques alone. I have already applied this approach to elucidate the solution structure of the MCMV m04 immunoevasin. I now propose to extend these methods to determine the structures of m04/MHC-I complexes. These structural investigations can reveal, in atomic detail, the mode of interaction of m04 with MHC-I thereby helping to resolve a longstanding puzzle regarding the function of the MCMV m04 immunoevasin, i.e. why does m04 enhance MHC-I surface expression instead of diminishing it? By analyzing structural aspects and the plasticity of the m04/MHC-I interaction, I aim to identify which of the several unique binding sites on MHC-I for cell surface immune receptors are blocked by the interaction with m04. Therefore, deciphering the mechanism of m04 binding to MHC will elucidate the basis of m04 specificity for particular MHC allotypes and provide insight into the function of the complex with respect to interfering with antigen presentation to T cells and NK cells. Although MCMV only infects mice, it has facilitated many important discoveries for the related human virus (HCMV), which causes a range of congenital infections and diseases in individuals with compromised immune systems (such as HIV patients and transplant recipients). By elucidating a key mechanism by which CMVs bypass immune responses and establish an infectious state, this study will provide insight to HMCV infection and further advance a new technology for structure-based studies of viral immune-interfering proteins.
This project addresses a fundamental process used by viruses to circumvent host Immune defenses that, due to the lack of a detailed structural characterization, lacks a firm understanding of the underlying molecular mechanism. Focusing on the m04 immunoevasin from mouse cytomegalovirus (CMV) as a model system, I have developed a new technology combining computational methods with sparse NMR experimental data, and I propose to use it to characterize the interactions of m04 with MHC-I molecules thereby providing insight into its unique immune interference function. Although the specific model virus being studied infects only mice, it shares many similarities with human cytomegalovirus that causes serious congenital defects and opportunistic infections in HIV patients and transplant recipients. Therefore, by focusing on this important preclinical model system, the results and general conclusions from this study will contribute to our better understanding of human viral infections.
| Natarajan, Kannan; McShan, Andrew C; Jiang, Jiansheng et al. (2017) An allosteric site in the T-cell receptor C? domain plays a critical signalling role. Nat Commun 8:15260 |
| Rossi, Paolo; Shi, Lei; Liu, Gaohua et al. (2015) A hybrid NMR/SAXS-based approach for discriminating oligomeric protein interfaces using Rosetta. Proteins 83:309-17 |
| Sgourakis, Nikolaos G; May, Nathan A; Boyd, Lisa F et al. (2015) A Novel MHC-I Surface Targeted for Binding by the MCMV m06 Immunoevasin Revealed by Solution NMR. J Biol Chem 290:28857-68 |
| Sgourakis, Nikolaos G; Natarajan, Kannan; Ying, Jinfa et al. (2014) The structure of mouse cytomegalovirus m04 protein obtained from sparse NMR data reveals a conserved fold of the m02-m06 viral immune modulator family. Structure 22:1263-1273 |
