Assembly and disassembly of the influenza C matrix protein layer on a lipid membrane

Abstract

Insight into the inner workings of viruses is an important piece of knowledge in humanity’s expanding collection of knowledge which can potentially be used to treat or prevent diseases. Influenza C is known to cause an infection with cold-like symptoms with possible complications in young children. The virus is a lipid-enveloped RNA virus in the Orthomyxoviridae family and incorporates 9 proteins. One of these is matrix protein 1 (M1C) which is found on the inside of the lipid-envelope of the virion. Influenza C in general and M1C in particular have not been extensively studied. However, influenza A and it’s matrix protein 1 have been studied to a great extent. In this thesis the binding and release of M1C on supported lipid bilayers (SLB) in various environments have been investigated. The SLB is a basic model of the lipid envelope of the influenza virions which is also suitable for the two surfacebased techniques used in this work. The two main environmental factors that were varied were the salinity and pH of the surrounding solution. The protein-protein and protein-bilayer binding behaviours were the two main interactions examined. In the Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) the amount of M1C bound to an SLB was measured. Information on the adlayer’s viscoelastic properties was also obtained. With this technique it was revealed that the binding of the protein is highly dependent on electrostatic charges. In the microscope, fluorescence and Surface Enhanced Ellipsometric Contrast (SEEC) microscopy was used to observe the spatial arrangement of the M1C on the SLB. The SEEC microscopy was used to observe aggregations of M1C on the SLB. A fraction of the negatively charged lipids in the SLB were tagged with the fluorescent dye NBD and the clustering of these was observed with fluorescence microscopy. This combined with the SEEC observations gave the conclusion that the proteins aggregate on the SLB and recruit negatively charged lipids. This work found that the main binding strategy for M1C is is to utilise electrostatic forces. This is important because this binding is used both in the forming of the virions and for maintaining the structural integrity of the virion. It was also found that endosomal pH leads to some dissociation of M1C from the lipid bilayer. This is important since the dissolution of the virion’s matrix protein layer in the endosome has been shown to be vital for infection in influenza A.