Identification of the Sites for Suppressor Mutations on the Hemagglutinin Molecule to Temperature‐Sensitive Phenotype of the Influenza Virus

Abstract

A temperature-sensitive (ts) mutant of the influenza virus A/WSN/ 33 strain, ts-134, possessed a defect in intracellular transport at the nonpermissive temperature and marked thermolability of hemagglutinin (HA) activity at 51 C. These were caused by a change at amino acid residue 157 from tyrosine to histidine in the HA protein. We isolated 37 spontaneous revertant clones from ts-134 at the nonpermissive temperature and determined their HA sequences. The deduced amino acid sequences demonstrated that one was a true revertant and the others were revertants with suppressor mutations, each of which had an additional amino acid change besides those of ts-134. The changed amino acids were located at 14 positions on the HA molecule, and eight of them were found in multiple revertants. These were located in five to six distinct regions on the three-dimensional structure of the HA molecule. However, the heat stability of HAs in the revertants was recovered differently depending on the sites of the changed amino acids. The kinetics of transport of the HA protein in the revertants were slightly delayed compared to the wild-type both at permissive and nonpermissive temperatures.

Inferring Stabilizing Mutations from Protein Phylogenies: Application to Influenza Hemagglutinin

“…The locations of these predicted stabilizing mutations in the three-dimensional structure are shown in Figure 10. None of these mutations is among the known revertants [106] described in the previous section.…”

“…These two temperature-sensitive mutations constitute our set of “destabilizing” mutations. For one of the two temperature-sensitive mutants (the one designated as ts-134 in [104]–[106]), a collection of second-site revertant mutations in hemagglutinin have been isolated by selecting for viruses that have regained the ability to grow at elevated temperatures [105],[106]. These revertant mutations presumably enhance hemagglutinin's folding and/or stability.…”

“…The temperature-sensitive mutation (ts-134 [104]–[106]) is shown with red spheres. The yellow spheres show the mutations that were predicted to be stabilizing by the PIPS program.…”