Tese
Diversidade genética de receptores de lactoferrina e transferrina em Moraxella bovis e Moraxella bovoculi
Fecha
2021-03-04Autor
Espíndola, Julia Pires
Institución
Resumen
Infectious bovine keratoconjunctivitis (IBK) is the most important eye disease in cattle, which
has a great economic impact due to eye injuries and loss of vision, resulting in pain, reduced
milk production, and decreased weight gain. The main etiological agents associated with IBK
are Moraxella bovis (M. bovis) and Moraxella bovoculi (M. bovoculi). Vaccination is essential
for the disease control; however, currently available vaccines may present limited efficiency.
Moraxella spp. have systems capable of extracting iron from the host glycoproteins named
lactoferrin and transferrin. Each receptor is composed of an integral outer membrane protein,
named lactoferrin or transferrin binding protein A (LbpA or TbpA), and of exposed surface
lipoprotein, named lactoferrin or transferrin binding protein B (LbpB or TbpB). These receptors
are known to be functionally and genetically related and are known for being essential in the
maintenance of pathogens on the mucosal surface leading to disease development. Studies
involving immunization with antigens derived from these receptors demonstrate a great
capacity to prevent infection, as well as to eliminate colonization of the upper respiratory tract.
A great potential of these receptors as vaccine antigens is expected due to their privileged
position on the cell surface, and their presumed ubiquity in all isolates of Moraxella spp.
However, to date, there have been no studies on the diversity of the pathogens responsible for
IBK, or they have been investigated as potential vaccine compounds. In this context, this thesis
was designed to investigate the genetic diversity and its distribution in the structure of TbpA
and TbpB proteins of M. bovis and M. bovoculi (manuscript 1) and the diversity of LbpA, as
well as the development of hybrid antigens (manuscript 2). For manuscript 1, DNA sequences
of thirty-seven M. bovis and M. bovoculi strains were translated into amino acids to build
phylogenetic trees for each protein. The alignments were then mapped on the predicted
structures of the proteins. In the phylogenetic analysis, TbpB sequences were separated by
species and more variable than TbpA. Also, two representative strains of TbpB were selected
that are likely to be able to cover all the variability found in these strains. In manuscript 2, a
similar analysis was performed with thirty-six LbpA sequences, and five hybrid antigens were
constructed using four different combinations of LbpA loops in a scaffold of the surface
lipoprotein from Vibrio cholerae (VcSLP). LbpA was very conserved also throughout its whole
structure. Hybrid antigens were expressed on a small scale efficiently and had the potential to
be large scaled for analysis of immunogenicity and cross-reactivity as vaccine antigens. In
conclusion, it was demonstrated in two different studies the diversity of TbpA, TbpB, and LbpA
and the approaches that can be taken to produce vaccine antigens derived from these proteins
intending to cover all the genetic diversity of the species.