Expressão da proteína do envelope do vírus da Febre Amarela em células de inseto
Yellow fever is an haemorrhagic disease caused by a virus that belongs to the genus Flavivirus (Flaviviridae family) and is transmitted by mosquitoes. It is a positive-sense, single-stranded, enveloped RNA virus, and its genome consists of 10,862 nucleotides coding for a single ORF of 10,233 nucleotides. This ORF encodes three structural proteins (capsid, pre-M, and envelope) and seven non-structural proteins (NS1, NS2a, NS2b, NS3, NS4a, NS4b, NS5). Among the viral proteins, the envelope protein is the most studied one, due to its high antigenic potencial. Isolated recombinant viral antigens may be useful in new vaccine and/or diagnosis development. On the purpose of isolating viral parts and expressing them separately, different heterologous expression systems may be used and within these, the Baculovirus Expression System in insect cells is one of the most popular and efficient. Baculoviruses have a circular, double stranded DNA genome and infect arthropodes, mainly insects. There are many advantages of using the baculovirus expression system such as high expression levels and post-translational modifications that allow the expressed proteins to be correctly folded and biologically active. The Yellow fever envelope gene was isolated by RT-PCR (1,600 base pairs). This fragment was cloned into two different transfer vectors: +pSynXIV VIX3 and p2100, that were co-transfected, in insect cells, with DNA from recombinant baculoviruses vSynVI-gal, derived from Autographa californica multiple +nucleopolyhedrovirus (AcMNPV), for the pSynXIVVI X3 and vAgGalA2, derived from Anticarsia gemmatalis multiple nucleopolyhedrovirus (AgMNPV), for the p2100]. Seven days after transfection, the cell culture supernatant was collected and used to purify the recombinant virus by the end-point dilution method in 96-well plates. The recombinant viruses, vSynYFE e vAgGalA2 were used to infect Trichopluisa ni insect cells (BTI-Tn5B1-4) and Spodoptera frugiperda larvae (for vSynYFE) and Anticarsia gemmatalis larvae (for vAgYFE). Insect cells infected with vSynYFE virus showed cytopathic effects manifested by multinucleated syncytial cells (which is typical of Flavivirus infection) and analysis of these cells extracts by SDS-PAGE detected the presence of a polypeptide around 50 kDa, similar to the size of the original Yellow fever envelope protein. However, fat body extracts of infected larvae (96 h p.i.) analysed by SDS-PAGE and Western blot detected a polypeptide around 70 kDa, different from the predicted size of the envelope protein.
Advisor:Bergmann Morais Ribeiro; Silene de Paulino Lozzi; Cynthia Maria Kyaw; Carlos Andre Ornelas Ricart
School:Universidade de Brasília
Source Type:Master's Thesis
Date of Publication:05/15/2007