Structural analysis of capsid proteins and VLPs from mutant 2B swine Circovirus with distinct in vitro and in vivo pathogenic effects

Abstract

Efficient swine farming techniques related to genetics, nutrition, management and sanity have been developed in the last years. However, due to the intensive farming system, these animals are now more susceptible to several infectious diseases. One of the most important pathogens which affect the swine industry worldwide is the porcine circovirus 2 (PCV2), a small icosahedral non-enveloped virus with a circular, ambisense, and single-stranded DNA molecule composed by 1767-1768 nucleotides. This highly resistant pan-endemic virus is associated to many swine clinical disorders which cause heavily economic losses to the producers. According to studies involving genetic engineering virus and protein/protein interaction experiments, one of the factors possibly implicated in the PCV2 pathogenicity is the cap protein, the fundamental unit of the viral capsid. Recent works performed by the virology laboratory headed by Prof. Dr. João Pessoa Araújo Jr. from Microbiology and Immunology Department, Biosciences Institute - UNESP (Botucatu/SP, Brazil), have identified in cell cultures the presence of three mutant PCV2s with cap protein modifications. These mutant viruses were able to increase the mortality rate of mice and provoke different cytopathic effects in comparison to a known wild type isolated from field samples. Initially, this research project aims the heterologous expression of the cap proteins from the wild type PCV2 isolated from the sample fields and the three mutant varieties associated to the mentioned in vitro and in vivo effects. Following, crystallographic studies will be conducted in order to compare the VLPs from each viral form, thus allowing the identification of possible capsid structural alterations which could shed some light on the puzzling pathogenic characteristics of the mutant PCV2s. Also, molecular dynamic computational simulations will be executed with theoretical monomeric cap protein models from the wild type and mutant viral forms to reveal important information related to the flexibility and stability of these molecules in the intracellular environment. This part of the project will permit the structural comparison of the cap proteins when they are not associated to form the capsid, since the interaction of these molecules with host cellular proteins seems also to play a significant role in the PCV2 pathogenicity. Therefore, the data from these experimental and theoretical works may be very useful for the comprehension of essential questions about the biology, epidemiology and pathogenicity of the PCV2. Additionally, the in vitro production of the VLPs from the mutant PCV2s is also included in this research project in order to make possible future experiments and help the development of new vaccines to control more effectively the porcine circovirosis. (AU)