Polar Residues and Their Positional Context Dictate the Transmembrane Domain Interactions of Influenza

Polar-mediated TMD interactions are related to their membrane-integration properties.Interactions that facilitate transmembrane domain (TMD)dimerization have been identified mainly using syntheticTMDs. Here, we investigated how inherent properties withinnaturalTMDsmodulatetheirinteractionstrengthbyexploitingthesequencevariationinthenineneuraminidasesubtypes(N1–N9) and the prior knowledge that a N1 TMD oligomerizes. Ini-tially,consensusTMDswerecreatedfromtheinfluenzaAvirusdatabase, and their interaction strengths were measured in abiological membrane system. The TMD interactions increasedwith respect to decreasing hydrophobicity across the subtypes(N1–N9)andwithinthehumanN1subtypewheretheN1TMDsfromthepandemicH1N1strainofswineoriginwerefoundtobesignificantly less hydrophobic. The hydrophobicity correlationwas attributed to the conserved amphipathicity within theTMDs as the interactions were abolished by mutating residueson the polar faces that are unfavorably positioned in the mem-brane. Similarly, local changes enhanced the interactions onlywhenalargerpolarresidueexistedontheappropriatefaceinanunfavorable membrane position. Together, the analysis of thisuniquenaturalTMDdatasetdemonstrateshowpolar-mediatedTMDinteractionsfrombitopicproteinsdependonwhichpolarresidues are involved and their positioning with respect to thehelix and the membrane bilayer.