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Incessant antigenic evolution enables the persistence and spread of influenza virus in the human population. As the principal target of the immune response, the hemagglutinin (HA) surface antigen on influenza viruses continuously acquires and replaces N-linked glycosylation sites to shield immunogenic protein epitopes using host-derived glycans. Anti-glycan antibodies, such as 2G12, target the HIV-1 envelope protein (Env), which is even more extensively glycosylated and contains under-processed oligomannose-type clusters on its dense glycan shield. Here, we illustrate that 2G12 can also neutralize human seasonal influenza A H3N2 viruses that have evolved to present similar oligomannose-type clusters on their HAs from around 20 years after the 1968 pandemic. Using structural biology and mass spectrometric approaches, we find that two N-glycosylation sites close to the receptor binding site (RBS) on influenza hemagglutinin represent the oligomannose cluster recognized by 2G12. One of these glycan sites is highly conserved in all human H3N2 strains and the other emerged during virus evolution. These two N-glycosylation sites have also become crucial for fitness of recent H3N2 strains. These findings shed light on the evolution of the glycan shield on influenza virus and suggest 2G12-like antibodies can potentially act as broad neutralizers to target human enveloped viruses. Author summary: The isolation of broadly neutralizing antibodies from HIV-1 patients has shed light on the design of HIV-1 vaccines. Among them, one group consisting of anti-carbohydrate antibodies target N-glycans that compose the glycan shield on the Envelope surface glycoprotein (Env) of HIV-1. Similar to HIV-1, human H3N2 influenza viruses are highly glycosylated due to the accumulation of N-glycosylation sites over the past 50 years of natural evolution. Here, we demonstrate that an anti-HIV-1 antibody, namely 2G12, can neutralize human H3N2 viruses from the past 35 years. Comprehensive analyses by mass spectrometry and negative-stain electron microscopy reveal that oligomannose on two N-glycosylation sites near the receptor binding site are the targets of 2G12. Of note, the distance and disposition between the two glycans are the same as the equivalent oligomannose cluster on HIV-1 Env. Furthermore, mutational study shows that these two N-glycosylation sites are both required for survival of the recent H3N2 strains. Our data suggest that 2G12 can broadly neutralize non-HIV-1 human viruses by targeting oligomannose sugars, if of sufficient density and disposition on the viral surface. Since many viral surface antigens are highly glycosylated, it is worth evaluating 2G12-like antibodies as potential general therapeutics for human viral pathogens. [ABSTRACT FROM AUTHOR]

Bacterial pathogens are highly adaptable organisms, a quality that enables them to overcome changing hostile environments. For example, Vibrio cholerae, the causative agent of cholera, is able to colonize host small intestines and combat host-produced reactive oxygen species (ROS) during infection. To dissect the molecular mechanisms utilized by V. cholerae to overcome ROS in vivo, we performed a whole-genome transposon sequencing analysis (Tn-seq) by comparing gene requirements for colonization using adult mice with and without the treatment of the antioxidant, N-acetyl cysteine. We found that mutants of the methyl-directed mismatch repair (MMR) system, such as MutS, displayed significant colonization advantages in untreated, ROS-rich mice, but not in NAC-treated mice. Further analyses suggest that the accumulation of both catalase-overproducing mutants and rugose colony variants in NAC- mice was the leading cause of mutS mutant enrichment caused by oxidative stress during infection. We also found that rugose variants could revert back to smooth colonies upon aerobic, in vitro culture. Additionally, the mutation rate of wildtype colonized in NAC- mice was significantly higher than that in NAC+ mice. Taken together, these findings support a paradigm in which V. cholerae employs a temporal adaptive strategy to battle ROS during infection, resulting in enriched phenotypes. Moreover, ΔmutS passage and complementation can be used to model hypermuation in diverse pathogens to identify novel stress resistance mechanisms. [ABSTRACT FROM AUTHOR]