Evolution of Sindbis virus with a low-methionine-resistant phenotype is dependent both on a pre-existing mutation and on the methionine concentration in the medium

Mutations on VEEV nsP1 relate RNA capping efficiency to ribavirin susceptibility

Alphaviruses are arthropod-borne viruses of public health concern. To date no efficient vaccine nor antivirals are available for safe human use. During viral replication the nonstructural protein 1 (nsP1) catalyzes capping of genomic and subgenomic RNAs. The capping reaction is unique to the Alphavirus genus. The whole three-step process follows a particular order: (i) transfer of a methyl group from S-adenosyl methionine (SAM) onto a GTP forming ^m7GTP; (ii) guanylylation of the enzyme to form a ^m7GMP-nsP1adduct; (iii) transfer of ^m7GMP onto 5'-diphosphate RNA to yield capped RNA. Specificities of these reactions designate nsP1 as a promising target for antiviral drug development. In the current study we performed a mutational analysis on two nsP1 positions associated with Sindbis virus (SINV) ribavirin resistance in the Venezuelan equine encephalitis virus (VEEV) context through reverse genetics correlated to enzyme assays using purified recombinant VEEV nsP1 proteins. The results demonstrate that the targeted positions are strongly associated to the regulation of the capping reaction by increasing the affinity between GTP and nsP1. Data also show that in VEEV the S21A substitution, naturally occurring in Chikungunya virus (CHIKV), is a hallmark of ribavirin susceptibility. These findings uncover the specific mechanistic contributions of these residues to nsp1-mediated methyl-transfer and guanylylation reactions.

Oral Methioninase for Covid-19 Methionine-restriction Therapy

The Covid-19 pandemic is a world-wide crisis without an effective therapy. While most approaches to therapy are using repurposed drugs that were developed for other diseases, it is thought that targeting the biology of the SARS-CoV-2 virus, which causes Covid-19, can result in an effective therapeutic treatment. The coronavirus RNA cap structure is methylated by two viral methyltransferases that transfer methyl groups from S-adenosylmethionine (SAM). The proper methylation of the virus depends on the level of methionine in the host to form SAM. Herein, we propose to restrict methionine availability by treating the patient with oral recombinant methioninase, aiming to treat Covid-19. By restricting methionine we not only interdict viral replication, which depends on the viral RNA cap methyaltion, but also inhibit the proliferation of the infected cells, which have an increased requirement for methionine. Most importantly, the virally-induced T-cell- and macrophage-mediated cytokine storm, which seems to be a significant cause for Covid-19 deaths, can also be inhibited by restricting methionine, since T-cell and macrophrage activation greatly increases the methionine requirement for these cells. The evidence reviewed here suggests that oral recombinant methioninase could be a promising treatment for coronavirus patients.

Epigenetic alterations and decreasing insecticide sensitivity of the Asian tiger mosquito Aedes albopictus

A range of environmental factors, including chemicals, can affect epigenetic processes in organisms leading to variations in phenotype. Thus, epigenetics displays an important environmentally responsive element. The transgenerational impact of environmental stressors on DNA methylation and phenotype was the focus of this study. The influence of two known DNA methylation-changing agents, the phytoestrogen genistein and the fungicide vinclozolin, on the overall DNA methylation level in the Asian tiger mosquito Aedes albopictus was investigated. The experiment comprised four generations in a full life-cycle design with an exposed parental generation and three consecutive non-exposed offspring generations. Application of the methylation agents to the parental generation of the study led to an alteration of the global DNA methylation level of the exposed individuals and those in two subsequent generations. The phenotypic variability of the offspring generations was assessed by examining their insecticide sensitivity. Here, a significant decrease in sensitivity (p<0.01) towards the model insecticide imidacloprid revealed alterations of the mosquito's phenotype in two subsequent generations. Thus, the evaluation of A. albopictus from an epigenetic perspective can contribute important information to the study of the high adaptability of this invasive disease vector to new environments, and its underlying mechanisms.