Pertactin sandbox1: Difference between revisions
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Autotransporters make up the largest protein family in Gram-negative bacteria. They are usually comprised of a C-terminal beta-barrel-shaped transporter domain anchored in the outer membrane and an N-terminal passenger domain that crosses the outer membrane through the beta barrel (Figure 1a). The autotransporter is considered a virulence factor with the passenger domain contributing to the virulence of the pathogen. This N-terminal domain is similar in structure between different species, but the functions vary greatly. However, the C terminal beta-barrel domain is a highly conserved structure for transport across the membrane but can vary greatly in the sequence. Many factors including biogenesis, use of accessory proteins, and fate of the beta-barrel translocator are not well known. | Autotransporters make up the largest protein family in Gram-negative bacteria. They are usually comprised of a C-terminal beta-barrel-shaped transporter domain anchored in the outer membrane and an N-terminal passenger domain that crosses the outer membrane through the beta barrel (Figure 1a). The autotransporter is considered a virulence factor with the passenger domain contributing to the virulence of the pathogen. This N-terminal domain is similar in structure between different species, but the functions vary greatly. However, the C terminal beta-barrel domain is a highly conserved structure for transport across the membrane but can vary greatly in the sequence. Many factors including biogenesis, use of accessory proteins, and fate of the beta-barrel translocator are not well known. | ||
Seeing that the structure of the passenger domain is similar between various bacteria, it was found that about 97% of them contain an extended right handed beta-helical structure. Specifically, pertactin has a passenger domain with a 16-turn parallel β-helix with a V-shaped cross-section and a hydrophobic core. Each turn contains approximately 25 residues which make up three beta strands that are linked by loops. It is predicted that the alpha-helical passenger domain traverses the hydrophilic pore of the transporter domain after the transporter domain is inserted into the outer membrane <ref name="BEN">Benz, I., & Schmidt, M. (n.d.). Structures and functions of autotransporter proteins in microbial pathogens. International Journal of Medical Microbiology, 461-468</ref>. | Seeing that the structure of the passenger domain is similar between various bacteria, it was found that about 97% of them contain an extended right handed beta-helical structure. Specifically, pertactin has a passenger domain with a 16-turn parallel β-helix with a V-shaped cross-section and a hydrophobic core. Each turn contains approximately 25 residues, which make up three beta strands that are linked by loops. It is predicted that the alpha-helical passenger domain traverses the hydrophilic pore of the transporter domain after the transporter domain is inserted into the outer membrane <ref name="BEN">Benz, I., & Schmidt, M. (n.d.). Structures and functions of autotransporter proteins in microbial pathogens. International Journal of Medical Microbiology, 461-468</ref>. | ||
[[Image:autotransporter.jpg]] | [[Image:autotransporter.jpg]] | ||
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One of these features is the <scene name='71/716564/Arg_gly_asp/1'>Arg-Gly-Asp (RGD) tripeptide motif</scene> that allows for protein-protein interactions <ref name="EMS" />. This motif has been found in several proteins, and has been shown to support cell adhesion in most cases. A subset of cell-surface proteins, called integrins, act as receptors for cell adhesion molecules. These integrins recognize the RGD motif within their ligands, and allow for cell-substratum and cell-cell interactions <ref>D'Souza, S. E., Ginsberg, M. H., & Plow, E. F. (1991). Arginyl-glycyl-aspartic acid (RGD): a cell adhesion motif. Trends In Biochemical Sciences, 16(7), 246-250.</ref>. | One of these features is the <scene name='71/716564/Arg_gly_asp/1'>Arg-Gly-Asp (RGD) tripeptide motif</scene> that allows for protein-protein interactions <ref name="EMS" />. This motif has been found in several proteins, and has been shown to support cell adhesion in most cases. A subset of cell-surface proteins, called integrins, act as receptors for cell adhesion molecules. These integrins recognize the RGD motif within their ligands, and allow for cell-substratum and cell-cell interactions <ref>D'Souza, S. E., Ginsberg, M. H., & Plow, E. F. (1991). Arginyl-glycyl-aspartic acid (RGD): a cell adhesion motif. Trends In Biochemical Sciences, 16(7), 246-250.</ref>. | ||
Additionally, P.69 contains two <scene name='71/716564/Proline/3'>proline-rich regions</scene> which are thought to provide important binding sites, and are characteristic of proteins exhibiting binding capabilities <ref name="EMS" />. Proline is a very unusual amino acid, and its structure limits the possible conformations it can adopt. | Additionally, P.69 contains two <scene name='71/716564/Proline/3'>proline-rich regions</scene> which are thought to provide important binding sites, and are characteristic of proteins exhibiting binding capabilities <ref name="EMS" />. Proline is a very unusual amino acid, and its structure limits the possible conformations it can adopt. The rigidity of these structures allow for reliable binding sites in many different proteins especially when chains of proline are bound to each other. These regions are typically non-specific, and allow for rapid binding. This is advantageous due to the wide range of ligands that can be bound, increasing the versatility of the proteins that utilize these regions <ref>Williamson, M. P. (1994). The structure and function of proline-rich regions in proteins. Biochemical Journal, 297(Pt 2), 249–260.</ref>. | ||
The linear form of pertactin that protrudes from the surface of ''B. pertussis'' also has a high surface area that could be well suited for targeting mammalian cells <ref name="EMS" />. Studies have shown that adhesive area strongly affects integrin binding and adhesion strength. The positioning of binding regions also affects adhesion strength, making the combination of these two factors particularly important for proteins that serve this function <ref>Gallant, N. D., Michael, K. E., & García, A. J. (2005). Cell Adhesion Strengthening: Contributions of Adhesive Area, Integrin Binding, and Focal Adhesion Assembly. Molecular Biology of the Cell, 16(9), 4329–4340.</ref>. | The linear form of pertactin that protrudes from the surface of ''B. pertussis'' also has a high surface area that could be well suited for targeting mammalian cells <ref name="EMS" />. Studies have shown that adhesive area strongly affects integrin binding and adhesion strength. The positioning of binding regions also affects adhesion strength, making the combination of these two factors particularly important for proteins that serve this function <ref>Gallant, N. D., Michael, K. E., & García, A. J. (2005). Cell Adhesion Strengthening: Contributions of Adhesive Area, Integrin Binding, and Focal Adhesion Assembly. Molecular Biology of the Cell, 16(9), 4329–4340.</ref>. | ||
== Function== | == Function== | ||
The closely related organisms ''B. pertussis, B. parapertussis, and B. bronchiseptica'' all produce slightly different forms of pertactin (p.69, P.70, P.68 respectively) | The closely related organisms ''B. pertussis, B. parapertussis, and B. bronchiseptica'' all produce slightly different forms of pertactin, which differ in the passenger domain (p.69, P.70, P.68 respectively). Specifically, the difference in size is due to the number of internal repeats within the passenger domain. These different forms of pertactin all share two RGD motifs that are thought to be relevant to cell binding. One is found in the passenger domain and one in the transporter domain. There is further evidence that pertactin functions in adhesion, however, the data is contradictory. ''In vitro'' adhesion assays show that pertactin allows for adhesion to general cell lines such as CHO and HeLa cells, however, no evidence for was found to convey that pertactin aids in adhesion of bacterial cells to either bronchial or laryngeal cells. Furthermore, no receptor has been identified for pertactin <ref name= "HEN">Henderson, I., & Nataro, J. (2001). Virulence Functions of Autotransporter Proteins. Infection and Immunity, 1231-1243.</ref>. This data supports the conflict of whether or not the function of pertactin is adhesion to host cells. | ||
In ''B. bronchiseptica'', pertactin seemed to be involved in the cytotoxicity | In ''B. bronchiseptica'', pertactin seemed to be involved in the cytotoxicity of mononuclear phagocytic cells. A possible explanation is that pertactin promoted stable adhesion of the bacterium to the phagocyte. Researchers also found that pertactin is produced ''in vitro'' at an intermediate time in ''B. pertussis'' growth: after another virulence factor, FHA, but before pertussis toxin. This occurrence supports the idea that pertactin is involved in a closer adhesion to mammalian cells but prior to toxin release <ref name="HEN" />. If pertactin truly is an adhesion molecule, it would be a huge contribution to the overall pathogenesis of the species. | ||
Regardless if pertactin functions as an adhesion, | Regardless if pertactin functions as an adhesion molecule, it is very biologically relevant. Pertactin would make for a good vaccine candidate. Manipulation of the passenger domain can be performed so that a gene for a certain protein from a different species can be inserted in the passenger domain thus replacing the wild type passenger domain <ref name="BEN" />. This would make for a very good vaccine candidate. Not only would the translocator of ''B. pertussis'' can be recognized as an antigen by the host as well as the heterologous protein inserted in the passenger domain. This could be the basis for a heterologous vaccine (combating two species). | ||
C-terminal beta helix function: | C-terminal beta helix function: | ||
