Doctoral defece: Sainan Wang „Structure-guided insights into the functions of CHIKV nsP2“

On February 19 at 2:15 p.m., Sainan Wang will defend her doctoral thesis in biomedical technology „Structure-guided insights into the functions of CHIKV nsP2“ 

Supervisor: Professor Andres Merits, University of Tartu

Opponent: Associate Professor Kenneth A. Stapleford, New York University Grossman School of Medicine, USA

Summary: Alphaviruses are enveloped viruses with positive-strand RNA genomes that are responsible for many human and animal diseases. One of the most medically important alphaviruses is chikungunya virus (CHIKV), which can cause chikungunya fever, an acute febrile disease typically accompanied by rash and debilitating and chronic arthralgia that can last for months or even years. Since its first massive outbreak at 2004, CHIKV has caused millions of cases in over 50 countries and has become a re-emerging pathogen of global importance. However, there are no licensed drugs to treat the disease caused by CHIKV infection.
Alphavirus genomic RNA replication depends on the process of RNA synthesis and modification carried out by non-structural proteins (nsPs) encoded by viral RNA. nsP2 is considered as the main driving force and master-regulator of RNA replication. However, the coordination of multiple enzymatic activities and other functions of nsP2 was poorly understood. The current study provided structural basis for better understanding of the roles of nsP2 in the alphavirus replication process; it also indicated that nsP2 can be engineered to perform additional functions required for virus replication. The main conclusions of this study could be illustrated as follows:
1: We identified the crucial residues that formed the stacking interactions between nsP2 and the RNA molecule corresponding to conserved 3’ end of CHIKV genome. Disruption of these interactions was found to have detrimental effect on viral RNA replication.
2: The flexible interdomain linker, connecting the N-terminal helicase and C-terminal protease regions of nsP2, was found to be essential for CHIKV replication as well; only small changes such as the deletion of one amino acid residue and the insertion of up to 10 amino acids residues were tolerated without significant impact on viral replication. However, the deletion of three or five residues of linker was lethal for CHIKV.
3: The insertion of G3BP/Rin binding motifs into the flexible regions of nsP2 (in the linker region or between different domains of nsP2 protease) was not only tolerated but the inserted sequence was able to support replication of mutant CHIKV in both mammalian and insect cells. The same insertion could also restore the infectivity of viruses lacking G3BP binding motifs in nsP3 in mammalian cells.

Defence can be followed in Zoom: https://ut-ee.zoom.us/j/9530588152?pwd=ZzgzMjY4YytzUkZ5aVRCd2pOdVNQQT09  (meeting ID: 953 058 8152, passcode: kaitsmine).