Effect of C- and N-Terminal Polyhistidine Tags on Aggregation of Influenza A Virus Nuclear Export Protein

Nuclear export protein (NEP) of the influenza A virus, being one of the key components of the virus life cycle, is a promising model for studying characteristics of formation of amyloids by viral proteins. Using atomic force microscopy, comparative study of aggregation properties of the recombinant NEP variants, including the protein of natural structure, as well as modified variants with N- and C-terminal affinity His₆-tags, was carried out. All protein variants under physiological conditions are capable of forming aggregates of various morphologies: micelle-like nanoparticles, flexible protofibrils, rigid amyloid fibrils, etc. His₆-tag attached to the C-terminus has the greatest effect on aggregation kinetics and morphology of nanoparticles, which indicates important role of the C-terminal domain in the process of protein self-assembly. Molecular dynamics simulation did not reveal substantial influence of the His₆-containing fragments on the protein structure, but demonstrated some variations in the mobility of these fragments that may explain the observed differences in the aggregation kinetics of the different NEP variants. Hypothetical mechanisms for formation and interconversion of various aggregates are considered.