Increased Dissociation of Adamantanamines in Influenza A M2 S31N with Partial Block by Rimantadine

Global distribution, receptor binding, and cross-species transmission of H6 influenza viruses: risks and implications for humans

The H6 subtype of avian influenza virus (AIV) is a pervasive subtype that is ubiquitously found in both wild bird and poultry populations across the globe. Recent investigations have unveiled its capacity to infect mammals, thereby expanding its host range beyond that of other subtypes and potentially facilitating its global transmission. This heightened breadth also endows H6 AIVs with the potential to serve as a genetic reservoir for the emergence of highly pathogenic avian influenza strains through genetic reassortment and adaptive mutations. Furthermore, alterations in key amino acid loci within the H6 AIV genome foster the evolution of viral infection mechanisms, which may enable the virus to surmount interspecies barriers and infect mammals, including humans, thus posing a potential threat to human well-being. In this review, we summarize the origins, dissemination patterns, geographical distribution, cross-species transmission dynamics, and genetic attributes of H6 influenza viruses. This study holds implications for the timely detection and surveillance of H6 AIVs.

Mechanism and Kinetics of Copper Complexes Binding to the Influenza A M2 S31N and S31N/G34E Channels

Copper(II) is known to bind in the influenza virus His37 cluster in the homotetrameric M2 proton channel and block the proton current needed for uncoating. Copper complexes based on iminodiacetate also block the M2 proton channel and show reduced cytotoxicity and zebrafish-embryo toxicity. In voltage-clamp oocyte studies using the ubiquitous amantadine-insensitive M2 S31N variant, the current block showed fast and slow phases, in contrast to the single phase found for amantadine block of wild-type M2. Here, we evaluate the mechanism of block by copper adamantyl iminodiacitate and copper cyclooctyl iminodiacitate complexes and address whether the complexes can coordinate with one or more of the His37 imidazoles. The current traces were fitted to parametrized master equations. The energetics of binding and the rate constants suggest that the first step is copper complex binding within the channel, and the slow step in the current block is the formation of a Cu-histidine coordination complex. Solution-phase isothermal titration calorimetry and density functional theory (DFT) calculations indicate that imidazole binds to the copper complexes. Structural optimization using DFT reveals that the complexes fit inside the channel and project the Cu(II) toward the His37 cluster, allowing one imidazole to form a coordination complex with Cu(II). Electrophysiology and DFT studies also show that the complexes block the G34E amantadine-resistant mutant despite some crowding in the binding site by the glutamates.