Polar residues and their positional context dictate the transmembrane domain interactions of influenza a neuraminidases

Abstract

Interactions that facilitate transmembrane domain (TMD) dimerization have been identified mainly using synthetic TMDs. Here, we investigated how inherent properties within naturalTMDsmodulate their interaction strength by exploiting the sequence variation in the nine neuraminidase subtypes (N1- N9) and the prior knowledge that a N1 TMD oligomerizes. Initially, consensus TMDs were created from the influenza A virus database, and their interaction strengths were measured in a biological membrane system. The TMD interactions increased with respect to decreasing hydrophobicity across the subtypes (N1-N9) and within the human N1 subtype where the N1TMDs from the pandemicH1N1strain of swine origin were found to be significantly less hydrophobic. The hydrophobicity correlation was attributed to the conserved amphipathicity within the TMDs as the interactions were abolished by mutating residues on the polar faces that are unfavorably positioned in the membrane. Similarly, local changes enhanced the interactions only when a larger polar residue existed on the appropriate face in an unfavorable membrane position. Together, the analysis of this unique naturalTMDdata set demonstrates how polar-mediated TMD interactions from bitopic proteins depend on which polar residues are involved and their positioning with respect to the helix and the membrane bilayer. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.