The changes of enterovirus spectrum have reminded people of the need to have a thorough understanding of echovirus and other typical serotypes. Echovirus 30 (E30) is an important member of the human enterovirus-B (EV-B) species and has emerged as one of major causative agents of viral encephalitis and meningitis. E30 has broken out seasonally and periodically in Europe, Asia and South America in recent years.

However, people still know very little about the antigenic features, immune characteristics and invasion mechanism of enterovirus-B species. In addition, there are no approved vaccines or antiviral therapies available for the treatment of infections caused by EV-B species.

In two new studies published in Nature Communications, the research teams of Prof. WANG Xiangxi and Academician RAO Zihe from the Institute of Biophysics of the Chinese Academy of Sciences, in collaboration with ZHU Fengcai's team with Jiangsu Provincial Center for Disease Control and Prevention, conducted in-depth analyses of the atomic structure, cellular invasion mechanism and neutralization mechanism of E30. The finding laid a foundation for the prediction of receptor usage and immune features of enterovirus as well as the research and development of relevant drugs and vaccines.

The researchers utilized the technology of cryo-electron microscopy to capture and decipher the atomic structure of E30 particles in different life stages, which included young E-particles, uncoating A-particles and mature F-particles reconstructed to 2.9 angstroms, 2.9 angstroms and 3.5 angstroms on the basis of the gold-standard Fourier shell correlations (FSC). Structural analyses revealed that both E-particles and F-particles are in the stage of closure, share high similarities in their surface structure, and demonstrate ordered epitopes, showing the potential to be ideal vaccine candidates. The findings were identical with the results of immunological experiment on cells and animals.

A structural comparison between E30 and EV-A, EV-B and EV-C species showed that viral protein 1 (VP1) BC loop of them exhibits no conservation, indicating that it can be used to tell the differences of important structural traits of various enterovirus serotypes. Meanwhile, their VP1 GH loop and VP2 EF loop are relatively conservative, showing that they can be used to design broad-spectrum antibodies of EV-B species.

Besides, the researchers analyzed the structures in complex of E30 in the resolution of 3.3 angstroms and 3.6 angstroms and its uncoating receptor human neonatal Fc receptor (FcRn) and that of E30 and its decay-accelerating factor (DAF/CD55), showing the structural basis of E30 in the recognition and combination of specific receptors.

Further studies found that VP1 EF loop, VP1 GH loop and VP2 EF loop jointly build molecular foundation for enterovirus and its uncoating receptor recognition. By computing all pairwise distances in different viral target regions, the researchers obtained K-vector and distance matrix between different viruses and came up with the computing method to predict the uncoating receptor of enterovirus.

To get better ideas for designing drugs and vaccines, the researchers selected two highly neutralizing and potent E30-specific monoclonal antibodies, 6C5 and 4B10. Both the surface plasmon resonance (SPR) experiment and real-time PCR experiment showed that 6C5 and 4B10 can neutralize E30 infection efficiently by blocking viral binding to its two types of receptors.

Interestingly, relevant experiments revealed that they can coordinate and complement each other, indicating that they will produce additional effects when used together. High-resolution structures of E30-6C5-Fab and E30-4B10-Fab revealed that 6C5 and 4B-10 engage the capsid loci at the rim of the canyon and in-canyon respectively. The conformational epitope, which consists of two neutralizing antibodies, is relatively active in EV-B species.

The above-mentioned structural information of atomic resolution provides important reference to the design of broad-spectrum vaccines and drugs mainly in conservative regions while avoiding non-conservative areas.

Enterovirus is one of the most widespread viruses in humans. The outbreak of enterovirus, which can be grouped into different families with various serotypes, has taken place in many countries and regions. The injection of vaccines will create herd immunity effect for susceptible population and inhibit the spread of a serotype-specific when it breaks out in some areas. However, other serotypes of enterovirus are expected to come into being at the same time and they will grow into leading etiological agents of some diseases in a specific group of people.