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Project A1: Julia Tillmanns, doctoral researcher (PhD)

Molecular studies on the kinase-regulated cytomegalovirus nuclear egress complex and its exploitation as a novel antiviral target

Known antiviral drugs against the globally distributed human cytomegalovirus (HCMV) are currently limited in their targets, rendering future-directed antiviral strategies with new target structures increasingly important.

During lytic replication, herpesviruses effectively modulate the host cell cycle, which includes a reprogramming of the physiological cyclin-dependent kinases (CDKs) functions. In the HCMV-infected cell, CDKs exert particular regulatory influences on virus-host interactions. Against this background of knowledge, our research group developed the concept to utilize inhibitors of host CDKs and viral pUL97/vCDK as a novel type of antiviral drug candidates. An important regulatory point of CDKs is the nucleocytoplasmic transport of newly synthesized capsids. This rate-limiting process of nuclear egress represents a determinant for efficient viral replication. Part of the multicomponent nuclear egress complex (NEC) are CDKs (CDK1, CDK2, possibly more) and the viral CDK ortholog pUL97.

Important regulatory functions and interaction points between CDKs and the NEC include the following: (i) pUL97/vCDK as a major determinant of the NEC; the vCDK has been experimentally validated as an efficient antiviral target, with maribavir representing the first, recently approved antiviral kinase inhibitor, blocking nuclear egress; (ii) CDK1 and pUL97 are associated with the central binding platform of the NEC, which is the pUL50-pUL53 heterodimer (core NEC); (iii) several viral regulators, including the core NEC and cyclin-binding pUL97 itself, are dually phosphorylated by both host CDKs and vCDK/pUL97; (iv) as originally characterized as CDK inhibitors, covalently binding compounds, so-called warheads, also exhibit an antiviral activity that is based on a block of the core NEC interaction. In relation to this, first prototype studies have already shown sterically NEC-blocking small molecules, which are able to suppress the heterodimerization of pUL50–pUL53, being highly conserved in structure and function for NEC homologs of a-, b- and g-herpesviruses. On this basis, the identified covalently binding warheads are a set of mechanistically new potential core NEC inhibitors.

The main goal of this PhD thesis is to characterize the NEC as a potential antiviral target.

We will address this by (i) analysis of core NEC characteristics in terms of NEC-DNA and NEC-capsid binding; (ii) assessment of specific kinase functionalities required during nuclear egress and regulatory NEC interactions; (iii) validation of kinase inhibitor-derived covalently binding warheads as prototypes of core NEC-inhibiting small molecules.