Biology subjects

Griesman, T.

Publications and source records attributed to Griesman, T..

4 recordsLinked to original sources

bioRxiv2026

Helicase family proteins promote antiviral ADP-ribosylation of DNA purines

DarTG defense systems studied to date contain a DarT1 or DarT2 toxin that blocks phage replication by ADP-ribosylating DNA and a NADAR or macrodomain antitoxin, DarG, that reverses this modification at homeostasis. Here, we identify additional DarTG subfamilies, one of which comprises a DarT3 toxin, an ADP-ribosylhydrolase (ARH)-domain antitoxin, and a helicase family protein, DarH. The Escherichia coli DarHTG3 system confers broad phage defense, requires DarH and, unlike previously characterized DarTG systems, modifies adenine. Characterization of additional DarH-containing DarTG systems reveals that a subset also target guanine. Our data support a model in which ADP-bound DarH functions as a processivity factor by recruiting DarT to its single-stranded DNA substrate and allowing for ADP-ribosylation of multiple target sites. These findings reveal how a helicase family protein regulates an antiviral effector by promoting DNA engagement rather than unwinding and thereby expanding the functional repertoire of helicase family proteins in bacterial immunity.

microbiology↗

bioRxiv2023

Evolutionary arms race between SARS-CoV-2 and interferon signaling via dynamic interaction with autophagy.

SARS-CoV-2 emerged, and is evolving to efficiently infect humans worldwide. SARS-CoV-2 evades early innate recognition, interferon signaling activated only in bystander cells. This balance of innate activation and viral evasion has important consequences, but the pathways involved are incompletely understood. Here we find that autophagy genes regulate innate immune signaling, impacting the basal set point of interferons, and thus permissivity to infection. Mechanistically, autophagy genes negatively regulate MAVS, and this low basal level of MAVS is efficiently antagonized by SARS-CoV-2 ORF9b, blocking interferon activation in infected cells. However, upon loss of autophagy increased MAVS overcomes ORF9b-mediated antagonism suppressing infection. This has led to the evolution of SARS-CoV-2 variants to express higher levels of ORF9b, allowing SARS-CoV-2 to replicate under conditions of increased MAVS signaling. Altogether, we find a critical role of autophagy in the regulation of innate immunity and uncover an evolutionary trajectory of SARS-CoV-2 ORF9b to overcome host defenses.

microbiology↗

bioRxiv2022

IgG3 subclass antibodies recognize antigenically drifted influenza viruses and SARS-CoV-2 variants through efficient bivalent binding

The constant domains of antibodies are important for effector functions, but less is known about how they can affect binding and neutralization of viruses. Here we evaluated a panel of human influenza virus monoclonal antibodies (mAbs) expressed as IgG1, IgG2 or IgG3. We found that many influenza virus-specific mAbs have altered binding and neutralization capacity depending on the IgG subclass encoded, and that these differences result from unique bivalency capacities of the subclasses. Importantly, subclass differences in antibody binding and neutralization were greatest when the affinity for the target antigen was reduced through antigenic mismatch. We found that antibodies expressed as IgG3 bound and neutralized antigenically drifted influenza viruses more effectively. We obtained similar results using a panel of SARS-CoV-2-specific mAbs and the antigenically advanced B.1.351 strain of SARS-CoV-2. We found that a licensed therapeutic mAb retained neutralization breadth against SARS-CoV-2 variants when expressed as IgG3, but not IgG1. These data highlight that IgG subclasses are not only important for fine-tuning effector functionality, but also for binding and neutralization of antigenically drifted viruses. SignificanceInfluenza viruses and coronaviruses undergo continuous change, successfully evading human antibodies elicited from prior infections or vaccinations. It is important to identify features that allow antibodies to bind with increased breadth. Here we examined the effect that different IgG subclasses have on monoclonal antibody binding and neutralization. We show that IgG subclass is a determinant of antibody breadth, with IgG3 affording increased neutralization of antigenically drifted variants of influenza virus and SARS-CoV-2. Future studies should evaluate IgG3 therapeutic antibodies and vaccination strategies or adjuvants that may skew antibody responses toward broadly reactive isotypes.

microbiology↗

bioRxiv2018

Assessing the protective potential of H1N1 influenza virus hemagglutinin head and stalk antibodies in humans

Seasonal influenza viruses are a major cause of human disease worldwide. Most neutralizing antibodies (Abs) elicited by influenza viruses target the head domain of the hemagglutinin (HA) protein. Anti-HA head Abs can be highly potent, but they have limited breadth since the HA head is variable. There is great interest in developing new universal immunization strategies that elicit broadly neutralizing Abs against conserved regions of HA, such as the stalk domain. Although HA stalk Abs can provide protection in animal models, it is unknown if they are present at sufficient levels in humans to provide protection against naturally-acquired influenza virus infections. Here, we quantified H1N1 HA head and stalk-specific Abs in 179 adults hospitalized during the 2015-2016 influenza virus season. We found that HA head Abs, as measured by hemagglutinin-inhibition (HAI) assays, were associated with protection against naturally-acquired H1N1 infection. HA stalk-specific serum total IgG titers were also associated with protection, but this association was slightly attenuated and not statistically significant after adjustment for HA head-specific Ab titers. We found higher titers of HA stalk-specific IgG1 and IgA Abs in sera from uninfected participants than from infected participants; however, we found no difference in sera in vitro antibody dependent cellular cytotoxicity activity. In passive transfer experiments, sera from participants with high HAI activity efficiently protected mice, while sera with low HAI activity protected mice to a lower extent. Our data suggest that human HA head and stalk Abs both contribute to protection against H1N1 infection.\n\nImportanceAbs targeting the HA head of influenza viruses are often associated with protection from influenza virus infections. These Abs typically have limited breadth since mutations frequently arise in HA head epitopes. New vaccines targeting the more conserved HA stalk domain are being developed. Abs that target the HA stalk are protective in animal models, but it is unknown if these Abs exist at protective levels in humans. Here, we found that Abs against both the HA head and HA stalk were associated with protection from naturally-acquired human influenza virus infections during the 2015-2016 influenza season.

microbiology↗