Chemical Insight into the Emergence of Influenza Virus
Strains That Are Resistant to Relenza
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Abstract
A reagent
panel containing ten 4-substituted 4-nitrophenyl α-d-sialosides and a second panel of the corresponding sialic
acid glycals were synthesized and used to probe the inhibition mechanism
for two neuraminidases, the N2 enzyme from influenza type A virus
and the enzyme from <i>Micromonospora viridifaciens</i>.
For the viral enzyme the logarithm of the inhibition constant (<i>K</i><sub>i</sub>) correlated with neither the logarithm of
the catalytic efficiency (<i>k</i><sub>cat</sub>/<i>K</i><sub>m</sub>) nor catalytic proficiency (<i>k</i><sub>cat</sub>/<i>K</i><sub>m</sub><i>k</i><sub>un</sub>). These linear free energy relationship data support the
notion that these inhibitors, which include the therapeutic agent
Relenza, are not transition state mimics for the enzyme-catalyzed
hydrolysis reaction. Moreover, for the influenza enzyme, a correlation
(slope, 0.80 ± 0.08) is observed between the logarithms of the
inhibition (<i>K</i><sub>i</sub>) and Michaelis (<i>K</i><sub>m</sub>) constants. We conclude that the free energy
for Relenza binding to the influenza enzyme mimics the enzyme–substrate
interactions at the Michaelis complex. Thus, an influenza mutational
response to a 4-substituted sialic acid glycal inhibitor can weaken
the interactions between the inhibitor and the viral neuraminidase
without a concomitant decrease in free energy of binding for the substrate
at the enzyme-catalyzed hydrolysis transition state. The current findings
make it clear that new structural motifs and/or substitution patterns
need to be developed in the search for a bona fide influenza viral
neuraminidase transition state analogue inhibitor