Structural Determinants for the Membrane Insertion of the Transmembrane Peptide of Hemagglutinin from Influenza Virus

Membrane fusion is a process involved in a high range of biological functions,going from viral infections to neurotransmitter release. Fusogenic proteins increase the slow rate of fusion by coupling energetically downhill conformational changes of the protein to the kinetically unfavorable fusion of the membrane lipid bilayers. Hemagglutinin is an example of a fusogenic protein, which promotes the fusion of the membrane. the influenza virus with the membrane of the target cell. The N-terminus of the HA2 subunit of this protein contains a fusion domain described, to act as a destabilizer Of the target membrane bilayers, leading eventually to a full fusion of two membranes On the other hand, the c-terminus of the same subunit contains a helical transmembrane domain which was initially described to act as the anchor of the protein,to the membrane of the virus. However, in recent years the study Of this peptide segment has been gaining more attention since it has :also. been described: to be involved in the Membrane fusion, process. Yet,: the structural characterization of the interaction Of such a protein domain With Membrane lipids is still very limited. Therefore, in this Work, we present a study of this transmembrane peptide domain in the presence of DMPC membrane bilayers, and we evaluate the effect of several mutations, and the effect of peptide oligomerization in this interaction process. Our results allowed us to identify and confirm amino acid residue motifs that seem to regulate the interaction between the segment peptide and membrane bilayers. Besides these sequence requirements, we have also identified length and tilt requirements that ultimately contribute to the hydrophobic matching between the peptide and the membrane. Additionally, We looked at the association of several transmembrane peptide segments and evaluated their direct interaction and stability inside a membrane bilayer. From our results we could conclude that three independent TM peptide segments arrange themselves in a parallel arrangement, very similarly to what is Observed for the C-terminal regions of the hemagglutinin crystallographic structure of the protein, to where. the segments, are attached.