Adam YUAN, Ph.D, Principal Investigator

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Research Interests

• Structural insights into RNA silencing
• Multidrug resistance mechanisms

Research Projects

Both RNA-protein interactions and small compound-membrane protein recognition form the basis of a majority of biological processes. We are using a combination of structural, biochemical and biophysical approaches to study RNA-protein interaction and small compound-membrane protein recognition at atomic resolution in vitro, as well as using a combination of molecular and cellular biological approaches, together with our collaborators, to study these important life-related processes in vivo. One of our long-term goals is to gain a detailed understanding of the structural, biophysical and biological properties of key super-complexes within RNA interference pathway, and to relate this understanding to its in vivo function. Currently, we are focusing on structural insights into virus induced gene silencing (VIGS) and molecular mechanisms of multidrug resistance.

RNA silencing

RNA silencing refers to small interfering RNA(siRNA)-mediated post-transcriptional gene regulation, resulting in the silencing of viral genes and transgenes. RNA silencing is indeed an ancient RNA-based antiviral immune response. MicroRNA and siRNA processor and the RNA-induced silencing complex (RISC) are key components within RNA interference (RNAi) pathway since the former one produces the RNAi trigger and the latter one modulates eukaryotic gene expression. Since Dicer proteins are the key elements of microRNA processor and Argoanute proteins are the key elements of RISC, therefore, our structural determination efforts will mainly focus on Dicer proteins and Argonaute proteins. We have already solved several individual domains of Dicer proteins and have solved a bacterial full-length Argonaute protein in both free-state and externally siRNA-bound state. We attempt to solve the structures of multiple domains of Dicer proteins complexes with specifically bound pre-microRNAs or siRNAs. Furthermore, we plan to solve the full-length Argonaute proteins complexes with internally-bound guide RNA strands. We further attempt to solve the structures of Dicer protein partners and Argonaute protein partners, such as double-strand RNA binding proteins and helicases, as well as viral suppressors against RNA silencing. We will couple our structure findings with biochemical studies in vitro and cellular biological studies in vivo.

Multidrug resistance

The uptake of cancer drugs is controlled by the efflux capabilities of membrane-spanning multidrug resistance (MDR) transporters/pumps. Any process that limits the levels of MDR trnasporters/pumps, will increase the cellular concentrations of cancer drugs. One approach to controlling levels of MDR transporters/pumps is to focus on the corresponding MDR regulators, where transporter/pump activation occurs following complex formation of the regulators with their DNA targets. We have already solved more than a half dozen MDR regulator structures in both free-state and substrate-bound state. We plan to expand on our recent structures of MDR regulators in free-state and substrate-bound state, to their complexes with DNA operators. Moreover, we have solved 4 ATP-binding domain structures of multidrug pumps. Now, we propose to solve structures of membrane-spanning multidrug pumps in both free-state and drug-bound state. Such efforts could lead to the identification of novel MDR inhibitors, with the potential for reversing or preventing drug resistance. Because of the known correlation between MDR transporter/pump expression and drug resistance in cancer patients, our proposal offers opportunities for enhanced chemotherapeutic approaches for the treatment of cancer.