Researchers at the Nanoscience Center (NSC) of the University of Jyväskylä in Finland have developed a novel method for the study of enterovirus structures and their functions. The method will help in obtaining new information on virus trafficking in cells and tissues as well as on the mechanisms of virus opening inside cells. This new information is important, for example, for developing new antiviral drugs and vaccines. The study was published in Proceedings of the National Academy of Sciences on 13 January 2014 (1). The research was funded by the Academy of Finland and Tekes' FiDiPro project NOVAC (Novel methods for vaccination and virus detection).
Enteroviruses are pathogenic viruses infecting humans. The group consists of polioviruses, coxsackieviruses, echoviruses and rhinoviruses. Enteroviruses are the most common causes of flu, but they also cause serious symptoms such as heart muscle infections and paralysis. Recently, enteroviruses have been linked to chronic diseases such as diabetes (2).
The infection mechanisms and infectious pathways of enteroviruses are still rather poorly known. Previous studies in the group of Dr Varpu Marjomäki at the NSC have focused on the cellular factors that are important for the infection caused by selected enteroviruses (3). The mechanistic understanding of virus opening and the release of the viral genome in cellular structures for starting new virus production is still largely lacking. Furthermore, the knowledge of infectious processes in tissues is hampered by the lack of reliable tools for detecting virus infections.
The newly developed method involves a chemical modification of a known thiol-stabilised gold nanoparticle, the so-called Au102 cluster that was first synthesised and structurally solved by Roger D. Kornberg's team in 2007 (4) and later characterised at the NSC by the groups of Professor Hannu Häkkinen and Professor Mika Pettersson in collaboration with Kornberg (5).
The organic thiol surface of the Au102 particles is modified by attaching linker molecules that make a chemical bond to sulfur-containing cysteine residues that are part of the surface structure of the virus. Several tens of gold particles can bind to a single virus, and the binding pattern shows up as dark tags reflecting the overall shape and structure of the virus (see figure). The gold particles allow for studies on the structural changes of the viruses during their lifespan.
Figure. Left: Transmission electron microscopy (TEM) image of a single CVB3 virus showing tens of gold nanoparticles attached to its surface. The particles form a distinct “tagging pattern” that reflects the shape and the structure of the virus. The TEM image can be correlated to the model of the virus (right), where the yellow spheres mark the possible binding sites of the gold particles. The diameter of the virus is about 35 nanometres (one nanometre = one billionth of a millimetre). The figure is taken from the publication (1).
The study also showed that the infectivity of the viruses is not compromised by the attached gold particles, which indicates that the labelling method does not interfere with the normal biological functions of viruses inside cells. This facilitates new investigations on the virus structures from samples taken from inside cells during the various phases of the virus infection, and makes it possible to obtain new information on the mechanisms of virus uncoating (opening and release of the genome). The new method also allows for tracking studies of virus pathways in tissues. This is important for further the understanding of acute and chronic symptoms caused by viruses. Finally, the method is expected to be useful for developing new antiviral vaccines based on virus-like particles.
The method was developed at the NSC as a wide, cross-disciplinary collaboration between chemists, physicists and biologists. Researchers involved in the work are Tanja Lahtinen, Kirsi Salorinne, Jaakko Koivisto and Mika Pettersson from the Department of Chemistry, Sami Malola from the Department of Physics and Mari Martikainen and Varpu Marjomäki from the Department of Biology and Environmental Science. The research was coordinated by Docent Varpu Marjomäki and the NSC's Scientific Director, Professor Hannu Häkkinen.
Academy of Finland, January 14, 2014