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Zoé Durrenberger

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 ==Function associated to this protein==
-Protein A has been identified as a cell surface protein of Staphylococcus aureus which contributes to the staphylococcal virulence. The virulence is mediated by the ability to interact with plasma protein<ref>Uhlén, M., Guss, B., Nilsson, B., Götz, F., & Lindberg, M. (1984). Expression of the gene encoding protein A in Staphylococcus aureus and coagulase-negative staphylococci. Journal of bacteriology, 159(2), 713-9</ref>. Protein A is able to bind to the Fc (constant region of IgG which is involved in effector functions) and the Fab fragment (also a part of Ig which is responsible for antigen recognition). The interactions of protein A with plasma proteins are mediated by five homologous domains, which are called E, D, A, B and C. Each of the homologous repeat domains comprises 56-61 residues, which are followed by a polymorphic variable repeat region, which is called Xr, and a conserved region Xc, which includes a cell wall attachment sequence. Each domain is able to bind one IgG molecule through its Fcγ binding site . The binding of protein A to the Fc fragment plays a major role in the virulence of Staphylococcus aureus as it competes with phagocytic cells for available IgG-Fc sites. This results in a reduction of IgG- mediated opsonization.
+Protein A has been identified as a cell surface protein of Staphylococcus aureus which contributes to the staphylococcal virulence. The virulence is mediated by the ability to interact with plasma protein<ref>Uhlén, M., Guss, B., Nilsson, B., Götz, F., & Lindberg, M. (1984). Expression of the gene encoding protein A in Staphylococcus aureus and coagulase-negative staphylococci. Journal of bacteriology, 159(2), 713-9</ref>. Protein A is able to bind to the Fc (constant region of IgG which is involved in effector functions) and the Fab fragment (also a part of Ig which is responsible for antigen recognition). The interactions of protein A with plasma proteins are mediated by five homologous domains, which are called E, D, A, B and C. Each of the homologous repeat domains comprises 56-61 residues, which are followed by a polymorphic variable repeat region, which is called Xr, and a conserved region Xc, which includes a cell wall attachment sequence<ref>O'Seaghdha, M., van Schooten, C. J., Kerrigan, S. W., Emsley, J., Silverman, G. J., Cox, D., Lenting, P. J. and Foster, T. J. (2006), Staphylococcus aureus protein A binding to von Willebrand factor A1 domain is mediated by conserved IgG binding regions. FEBS Journal, 273: 4831–4841</ref>. Each domain is able to bind one IgG molecule through its Fcγ binding site . The binding of protein A to the Fc fragment plays a major role in the virulence of Staphylococcus aureus as it competes with phagocytic cells for available IgG-Fc sites. This results in a reduction of IgG- mediated opsonization.
 The domains D and E of protein A are able to bind to the Fab fragments of immunoglobulins through variable (V) regions. The Fv-binding sites enable protein A to cross-link membrane IgM on B cells and therefore mediate the activation of these cells, which confers a superantigen function to protein A. Several features of the interactions of protein A with host B lymphocytes are similar to those of superantigens for T lymphocytes, which can cause various inflammatory diseases, such as toxic shock syndrome and food poisoning.
 Furthermore it was shown that the staphylococcal protein A is able to activate the classical complement pathway. This activation depends on the binding of a VH3+ IgM molecule to protein A, which results in the generation of an inflammatory reaction. The protein A induced complement activation is another factor, which contributes to the staphylococcal virulence.