Substrate diversity of herpes simplex virus thymidine kinase. Impact Of the kinematics of the enzyme.

Herpes simplex virus type 1 (HSV 1) thymidine kinase (TK) exhibits an extensive substrate diversity for nucleobases and sugar moieties, in contrast to other TKs. This substrate diversity is the crucial molecular basis of selective antiviral and suicide gene therapy. The mechanisms of substrate binding of HSV 1 TK were studied by means of site-directed mutagenesis combined with isothermal calorimetric measurements and guided by theoretical calculations and sequence comparison. The results show the link between the exceptionally broad substrate diversity of HSV 1 TK and the presence of structural features such as the residue triad His-58/Met-128/Tyr-172. The mutation of Met-128 into a Phe and the double mutant M128F/Y172F result in mutants that have lost their activity. However, by exchanging His to form the triple mutant H58L/M128F/Y172F, the enzyme regains activity. Strikingly, this triple mutant becomes resistant toward acyclovir. Furthermore, we give evidence for the importance of Glu-225 of the flexible LID region for the catalytic reaction. The data presented give new insights to understand mechanisms ruling substrate diversity and thus are crucial for both the development of new antiviral drugs and engineering of mutant TKs apt to accept novel substrate analogs for gene therapeutic approaches

High-throughput docking for the identification of new influenza A virus polymerase inhibitors targeting the PA-PB1 protein-protein interaction

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Discovery and synthesis of novel benzofurazan derivatives as inhibitors of influenza A virus

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Discovery and synthesis of novel benzofurazan derivatives as inhibitors of influenza A virus

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Extended Substrate Acceptance of Herpes Simplex Virus Type 1 Thymidine Kinase: a New Chance for Gene and Antiviral Therapy

Herpes simplex virus type 1 thymidine kinase (HSV1-TK) has become increasingly important as a target in medicinal chemistry because of its links to therapy of viral infection, gene therapy of cancer and allogeneic transplantation. These applications are based on the differences in binding properties between the human and the viral enzyme. Several problems have been encountered in the clinic, e.g. the increase of resistance for antiviral drugs and the immunosuppressive effects of the dosages needed for tumor regression. Thus intensive efforts have been directed towards understanding substrate diversity to overcome the clinical limitations. In this context, kinetic and thermodynamic studies revealed that substrates bind in compulsory order and that the binding event is enthalpy driven. The structural evaluation of aciclovir resistant HSV strains shows that loss of electrostatic interactions, change in steric accessibility and modification of the 3D conformation of HSV1-TK are responsible for the encountered resistance. Further crystallography studies revealed the role of water in substrate binding, the advantage of a fixed ribose ring and that substrate acceptance of HSV1-TK is extended to all five nucleobases. The reviewed results give new rationale for the design of novel prodrugs and engineered HSV1-TK for antiviral and gene therapy

Hepatic Vasculopathy and Regenerative Responses of the Liver in Fatal Cases of COVID-19

Kaltschmidt B, Fitzek ADE, Schaedler J, et al. Hepatic Vasculopathy and Regenerative Responses of the Liver in Fatal Cases of COVID-19. Clinical Gastroenterology and Hepatology. 2021;(19):1726-1729