The Cytoplasmic Tail of Influenza A Virus Hemagglutinin and Membrane Lipid Composition Change the Mode of M1 Protein Association with the Lipid Bilayer

Abstract

Influenza A virus envelope contains lipid molecules of the host cell and three integral viral proteins: major hemagglutinin, neuraminidase, and minor M2 protein. Membrane-associated M1 matrix protein is thought to interact with the lipid bilayer and cytoplasmic domains of integral viral proteins to form infectious virus progeny. We used small-angle X-ray scattering (SAXS) and complementary techniques to analyze the interactions of different components of the viral envelope with M1 matrix protein. Small unilamellar liposomes composed of various mixtures of synthetic or “native” lipids extracted from Influenza A/Puerto Rico/8/34 (H1N1) virions as well as proteoliposomes built from the viral lipids and anchored peptides of integral viral proteins (mainly, hemagglutinin) were incubated with isolated M1 and measured using SAXS. The results imply that M1 interaction with phosphatidylserine leads to condensation of the lipid in the protein-contacting monolayer, thus resulting in formation of lipid tubules. This effect vanishes in the presence of the liquid-ordered (raft-forming) constituents (sphingomyelin and cholesterol) regardless of their proportion in the lipid bilayer. We also detected a specific role of the hemagglutinin anchoring peptides in ordering of viral lipid membrane into the raft-like one. These peptides stimulate the oligomerization of M1 on the membrane to form a viral scaffold for subsequent budding of the virion from the plasma membrane of the infected cell.

Influenza A Virus M1 Protein Non-Specifically Deforms Charged Lipid Membranes and Specifically Interacts with the Raft Boundary

“…We observed that, in the case of bPS-containing raft GUVs, the addition of the M1 protein led to the division of the vesicle into a raft and a non-raft one ( Figure 8 ). This is aligned with the observed widening of the electron density profile of the membrane with M1, as detected by SAXS in [ 38 ], due to the change of the initial spherical shape of the vesicle to a more prolate dumbbell one. BSA and PLL did not exhibit such behavior ( Figure 9 and Figure 10 ).…”

“…M1 electrostatically interacts with anionic lipids of the inner leaflet of the plasma/viral membrane [ 34 ]. Anionic phosphatidylserine (PS) enhances the M1 oligomerization on the membrane [ 35 , 36 ], probably leading to the formation of membrane invaginations [ 37 , 38 ]. The presence of phosphatidylinositol 4,5-bisphosphate (PIP2) clusters M1 protein, possibly due to the high surface charge density [ 39 ].…”

“…Nevertheless, M1 weakly adsorbs to noncharged lipids [ 40 , 41 ] and can partially incorporate into the contacting monolayer, possibly by its amphipathic helices [ 42 , 43 ], which means that hydrophobic interactions are also involved in the protein–membrane binding. These interactions would explain why ordered nanodomains affect the M1–lipid interaction [ 38 ] and play a vital role in influenza infectivity [ 26 ]. Such interactions would decrease the energy of the hydrophobic mismatch between spike glycoproteins, HA, and neuraminidase (NA) apparently residing in the L o domain [ 44 ] from one side and the surrounding L d phase from another.…”

Deciphering the Assembly of Enveloped Viruses Using Model Lipid Membranes

“…Since the pioneering work of Gregoriades and Oxford [ 54 , 55 ], PS has been identified as the main target for the membrane association of IAV M1 [ 16 , 56 , 57 ]. Recently, the effect of lipid composition on the initiation of M1 self-assembly has been studied using SUVs (small unilamellar vesicles) and proteoliposomes, showing the role of lipid ordering in the association of M1 to PS in these liposomes [ 58 ]. Liposomes were also used to monitor the interactions of virus proteins such as HA [ 55 ] and NA [ 59 ] with lipids and lipid redistribution; however, this was essentially considered during membrane fusion [ 60 ], which is the entry step (early phase of replication) of the virus, not the assembly step.…”

A new intracellular targeting motif in the cytoplasmic tail of the spike protein may act as a target to inhibit SARS-CoV-2 assembly

“…For instance, the CT of human immunodeficiency virus type 1 (HIV-1) envelope protein gp41 interacts with the Gag protein, which contribute to the enrichment of gp41 at the viral packaging site for subsequent efficient packaging into viral particles ( Muranyi et al, 2013 ; Postler and Desrosiers, 2013 ; Roy et al, 2013 ; Tedbury and Freed, 2015 ). In addition, the interactions between the CT of the HA protein or NA protein of influenza A virus and the M1 protein facilitate the maintenance of the correct subcellular localization and packaging of viral particles ( Barman et al, 2004 ; Jin et al, 1997 ; Kordyukova et al, 2021 ). Moreover, the CT of respiratory syncytial virus fusion protein mediates virion assembly through incorporation of internal virion proteins into virus filaments at the cell surface ( Baviskar et al, 2013 ; Shaikh et al, 2012 ).…”