Doctoral defence: Kai Rausalu “Alphaviral nsP2 protease: from requirements for functionality to inhibition”

On 15 June at 15:15 Kai Rausalu will defend her doctoral thesis “Alphaviral nsP2 protease: From requirements for functionality to inhibition” for obtaining the degree of Doctor of Philosophy (in Biomedical Technology).

Professor Andres Merits, University of Tartu

Professor Margaret Kielian, Albert Einstein College of Medicine (USA)

Alphaviruses (genus Alphavirus, family Togaviridae) have an RNA genome and the virions are approximately 70 nm in size. One of alphaviruses is Chikungunya virus (CHIKV), which causes a disease with debilitating joint pains that can last for months. It is important to find antiviral compounds to alleviate suffering caused by CHIKV. For that, we need to understand how the viral life cycle occurs in the cells. nsP2 is a multifunctional CHIKV protein, it is the viral protease and the RNA helicase, nsP2 also participates in the suppression of cellular immune response. As a protease, nsP2 is the viral protein, that cleaves the viral nonstructural polyprotein into individual proteins. This process plays a central role in the regulation of the viral life cycle. Within this thesis, we studied the requirements of CHIKV nsP2 for its protease activity. We found, that CHIKV nsP2 is a cysteine-protease, which is similar to previously studied alphaviral nsP2 proteases. In amino acid sequence CHIKV nsP2 must have intact cysteine 478 for its protease activity. If this cysteine or nearby tryptophan 479 is substituted with alanine, then CHIKV nsP2 loses its protease activity. Cleavage of alphaviral nonstructural polyprotein is a temporally regulated process. We studied how Semliki Forest virus (SFV) and Sindbis virus (SINV) are affected by changes in the speed of cleavages of the nonstructural polyprotein. We found, that it is important for SFV and SINV to prevent premature cleavage between viral nsP1 and nsP2. Accelerated processing of SFV or SINV nonstructural polyprotein caused decrease in infectivities and reduced viral RNA synthesis. The final part of the thesis is the analysis of novel CHIKV inhibitors. The structure of a previously known CHIKV inhibitor was modified in several ways and the anti-CHIKV properties of the novel compounds were evaluated. We identified a compound, that had approximately 10-fold increased anti-CHIKV activity in cell culture.

Defence can be also followed in Zoom: (Meeting ID: 953 0588 1521, Passcode: kaitsmine).

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