Abstract
The methyltransferase enzyme (MTase), which catalyzes the transfer of a methyl group from S-adenosyl-methionine (AdoMet) to viral RNA, and generates S-adenosyl-homocysteine (AdoHcy) as a by-product, is essential for the life cycle of many significant human pathogen flaviviruses. Here we investigated inhibition of the flavivirus MTase by several AdoHcy-derivatives. Unexpectedly we found that AdoHcy itself barely inhibits the flavivirus MTase activities, even at high concentrations. AdoHcy was also shown to not inhibit virus growth in cell-culture. Binding studies confirmed that AdoHcy has a much lower binding affinity for the MTase than either the AdoMet co-factor, or the natural AdoMet analog inhibitor sinefungin (SIN). While AdoMet is a positively charged molecule, SIN is similar to AdoHcy in being uncharged, and only has an additional amine group that can make extra electrostatic contacts with the MTase. Molecular Mechanics Poisson-Boltzmann Sovation Area analysis on AdoHcy and SIN binding to the MTase suggests that the stronger binding of SIN may not be directly due to interactions of this amine group, but due to distributed differences in SIN binding resulting from its presence. The results suggest that better MTase inhibitors could be designed by using SIN as a scaffold rather than AdoHcy.
Highlights
Members of the Flavivirus genus, such as Dengue virus (DENV), Yellow Fever virus (YFV), West Nile virus (WNV), Tick-borne encephalitis virus (TBEV), and Japanese encephalitis virus (JEV) are ss-RNA (+) arthropod-borne viruses that can cause serious human disease, including meningitis, myelitis, encephalitis, and hemorrhagic fever [1,2,3]
Effective vaccines exist for YFV, JEV, and TBEV [3] the difficulty of vaccinating large at-risk populations and the danger of adverse vaccination effects highlight the importance of developing antiviral therapeutics for treatment of severe flavivirus infections
The first methylation of the viral mRNA cap is an obligate step in the virus life-cycle; and defects in N-7 methylation are lethal to DENV, WNV, YFV, and Kunjin virus replication [18,19,21,23,24,25,26]
Summary
Members of the Flavivirus genus, such as Dengue virus (DENV), Yellow Fever virus (YFV), West Nile virus (WNV), Tick-borne encephalitis virus (TBEV), and Japanese encephalitis virus (JEV) are ss-RNA (+) arthropod-borne viruses that can cause serious human disease, including meningitis, myelitis, encephalitis, and hemorrhagic fever [1,2,3]. Flavivirus infections are endemic to all continents except Antarctica. These viruses infect more than 200 million people and result in more than 100,000 fatalities per year [3]. The flavivirus MTase was found to catalyze additional 2’-O methylations of internal adenosine of the viral RNA [22]. The first methylation of the viral mRNA cap is an obligate step in the virus life-cycle; and defects in N-7 methylation are lethal to DENV, WNV, YFV, and Kunjin virus replication [18,19,21,23,24,25,26].
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