3Introduction: As an example, the H1N1 virus responsible for the 1918 ""Spanish flu"" pandemic (SC18, ""South Carolina 1918"") propagated as efficiently between ferrets by aerosol as it did between humans, but a single mutation (
D225G) and a double mutation (
D225G/
D190E) of amino acids in the H1 receptor binding site (RBS) yielded two artificial viruses, NY18 and AV18, respectively, the former being transmitted inefficiently and the latter unable to do so, while its lethality and replicati
Introduction: At the molecular level, the H1 (SC18) specificity switch was explained by observing that the
D225G mutation on H1 removed crucial hydrogen bonds between the RBS and the LSTc nonreducing end, while the additional mutation (
D190E) further reduced the extent of contact between its reducing end and the surface of helix 190.