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Zoé Durrenberger

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 The structural details of protein A were solved by the nuclear magnetic resonance method. The length of the amino acid chain of protein A contains 508 residues. The amino acids cystein and tryptophan do not occur in the amino acid sequence. The molecular weight of the described protein is 55439 Dalton and it consists of only one protein chain.
-The 3D structure is build up of three α-helixes and it consists of five extracellular domains, which are designated as E, D, A, B and C. Furthermore the protein contains cell-wall spanning regions, called X<sub>r</sub> and X<sub>c</sub>, and a hydrophobic membrane spanning domain, which is distal to LPXTG and consists of 18-20 residues<ref>Hartleib, J., Köhler, N., Dickinson, R. B., Chhatwal, G. S., Sixma, J. J., M, O., Foster, T. J., et al. (2000). Protein A is the von Willebrand factor binding protein on Staphylococcus aureus, 2149-2156</ref>. Protein A exists in a secreted and a cell wall anchored form. If it is bound to the cell wall of Staphylococcus aureus it is covalently linked to the peptidoglycan via its C-terminal domain.
+The 3D structure is build up of three α-helixes and it consists of five extracellular domains, which are designated as E, D, A, B and C. Furthermore the protein contains cell-wall spanning regions, called X<sub>r</sub> and X<sub>c</sub>, and a hydrophobic membrane spanning domain, which is distal to LPXTG and consists of 18-20 residues<ref>Hartleib, J., Köhler, N., Dickinson, R. B., Chhatwal, G. S., Sixma, J. J., M, O., Foster, T. J., et al. (2000). Protein A is the von Willebrand factor binding protein on Staphylococcus aureus, 2149-2156</ref>. Protein A exists in a secreted and a cell wall anchored form. If it is bound to the cell wall of ''Staphylococcus aureus'' it is covalently linked to the peptidoglycan via its C-terminal domain.
 ==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<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.
+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.