Busath, D. D. | Search bioRxiv

bioRxiv2021

An Investigation of the Mechanism for a Novel Influenza Inhibitor Designed to Target the Import of PB1

A novel inhibitor of PB1 import, referred to here as GM30, previously displayed nuclear retention of viral nucleoprotein (NP), which spurred the question of whether the compound directly or indirectly blocked viral ribonucleoprotein (vRNP) complex export. vRNPs are exported from the nucleus via exportin 1 (XPO1). Using verdinexor (VNXR), a direct inhibitor of vRNP export that binds to XPO1 and also blocks nuclear factor kappa B (NF-{kappa}B) export, we found that GM30 does not block nuclear export of NF-{kappa}B. GM30 likewise demonstrated high nuclear retention of NP but not as much as the direct inhibition of nuclear export by VNXR. When the compound was added hours after infection, the compound lost its ability to block nuclear export but VNXR retained its ability to block nuclear export. GM30 is therefore likely an indirect inhibitor of nuclear export because it disrupts the vRNP complex formation and impedes export from the nucleus by reducing nuclear import of PB1.

microbiology↗

bioRxiv2020

Mechanism and kinetics of copper complexes binding to the influenza A M2 channel

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 WT M2. Here we evaluate the mechanism of block by copper adamantyl iminodiacitate (Cu(AMT-IDA)) and copper cyclooctyl iminodiacitate (Cu(CO-IDA)) complexes and address whether the complexes can covalently bind to 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 covalent bond formation between copper complex and histidine. Isothermal titration calorimetry (ITC) indicates that a single imidazole binds strongly to the copper complexes. Structural optimization using density functional theory (DFT) reveals that the complexes fit inside the channel and project the Cu(II) towards the His37 cluster allowing one imidazole to form a covalent bond with the Cu(II). Electrophysiology and DFT studies also show that the complexes block the G34E amantadine-resistant mutant in spite of some crowding in the binding site by the glutamates.

biophysics↗