We apologize for Proteopedia being slow to respond. For the past two years, a new implementation of Proteopedia has been being built. Soon, it will replace this 18-year old system. All existing content will be moved to the new system at a date that will be announced here.

Sandbox Reserved 982

From Proteopedia

(Difference between revisions)
Jump to: navigation, search
Current revision (22:02, 1 May 2015) (edit) (undo)
 
(3 intermediate revisions not shown.)
Line 7: Line 7:
Shiga toxin (stx) has multiple classifications. The shiga toxin produced by ''Shigella dysenteriae'' is classified as stx, while shiga toxin produced by Escherichia coli is classified as either stx1 or stx2. All three classifications vary slightly in structure but have identical functions. The A sub-unit of stx1 differs from stx by one residue: a serine in position 45 as opposed to threonine<ref name="Fraser">Fraser, M. E., Fujinaga, M., Cherney, M. M., Melton-Celsa, A. R., Twiddy, E. M., O’Brien, A. D., & James, M. N. G. (2004). Structure of shiga toxin type 2 (Stx2) from Escherichia coli O157:H7. The Journal of Biological Chemistry, 279(26), 27511–27517. doi:10.1074/jbc.M401939200</ref>.
Shiga toxin (stx) has multiple classifications. The shiga toxin produced by ''Shigella dysenteriae'' is classified as stx, while shiga toxin produced by Escherichia coli is classified as either stx1 or stx2. All three classifications vary slightly in structure but have identical functions. The A sub-unit of stx1 differs from stx by one residue: a serine in position 45 as opposed to threonine<ref name="Fraser">Fraser, M. E., Fujinaga, M., Cherney, M. M., Melton-Celsa, A. R., Twiddy, E. M., O’Brien, A. D., & James, M. N. G. (2004). Structure of shiga toxin type 2 (Stx2) from Escherichia coli O157:H7. The Journal of Biological Chemistry, 279(26), 27511–27517. doi:10.1074/jbc.M401939200</ref>.
-
Stx is a 70 kDa AB5 protein, meaning that it is composed of an A sub-unit bound to a B pentamer. A noncovalent interaction causes the association between the A and B sub-units, as the carboxy terminal tail of the A sub-unit is surrounded by the B pentamer. <scene name='68/687332/Sub-unit_a/2'>The A sub-unit</scene> is 293 amino acids long with its active site being <scene name='68/687332/Active_site_for_stx/1'>glutamic acid 167 (1R4Q)</scene>. Though the active site contains a single residue, studies have shown that the first 239 residues are essential for the enzymatic activity of the A sub-unit. Residues 240-251 are essential for the A sub-unit’s translocation from the endoplasmic reticulum of an infected cell to the cytosol<ref name="Sandvig">Sandvig, K., & van Deurs, B. (2000). Entry of ricin and Shiga toxin into cells: molecular mechanisms and medical perspectives. The EMBO Journal, 19(22), 5943–5950. doi:10.1093/emboj/19.22.5943</ref>.
+
Stx is a 70 kDa AB5 protein, meaning that it is composed of an A sub-unit bound to a B pentamer. A pentamer of B sub-units encircles the carboxy tail of the A sub-unit stabilized by a series of non-covalent interactions. <scene name='68/687332/Sub-unit_a/2'>The A sub-unit</scene> is 293 amino acids long with its active site being <scene name='68/687332/Active_site_for_stx/1'>glutamic acid 167 (1R4Q)</scene>. Though the active site contains a single residue, studies have shown that the first 239 residues are essential for the enzymatic activity of the A sub-unit. Residues 240-251 are essential for the A sub-unit’s translocation from the endoplasmic reticulum of an infected cell to the cytosol<ref name="Sandvig">Sandvig, K., & van Deurs, B. (2000). Entry of ricin and Shiga toxin into cells: molecular mechanisms and medical perspectives. The EMBO Journal, 19(22), 5943–5950. doi:10.1093/emboj/19.22.5943</ref>.
The A sub-unit can be broken down into A1 and A2 units. This break down occurs when a trypsin sensitive region, residues 248-251, is cleaved. This cleavage results in the only remaining link being a <scene name='68/687332/Disulfide_bridge/1'>disulfide bridge (1R4Q)</scene> between cysteine 242 and cysteine 261. If the disulfide bridge is reduced, the A1 and A2 fragments can completely separate. Interestingly, the disulfide bridge blocks the active site of the A sub-unit, so the A sub-unit is not enzymatically active unless it has been cleaved<ref name ="Fraser">Fraser, M. E., Fujinaga, M., Cherney, M. M., Melton-Celsa, A. R., Twiddy, E. M., O’Brien, A. D., & James, M. N. G. (2004). Structure of shiga toxin type 2 (Stx2) from Escherichia coli O157:H7. The Journal of Biological Chemistry, 279(26), 27511–27517. doi:10.1074/jbc.M401939200</ref>.
The A sub-unit can be broken down into A1 and A2 units. This break down occurs when a trypsin sensitive region, residues 248-251, is cleaved. This cleavage results in the only remaining link being a <scene name='68/687332/Disulfide_bridge/1'>disulfide bridge (1R4Q)</scene> between cysteine 242 and cysteine 261. If the disulfide bridge is reduced, the A1 and A2 fragments can completely separate. Interestingly, the disulfide bridge blocks the active site of the A sub-unit, so the A sub-unit is not enzymatically active unless it has been cleaved<ref name ="Fraser">Fraser, M. E., Fujinaga, M., Cherney, M. M., Melton-Celsa, A. R., Twiddy, E. M., O’Brien, A. D., & James, M. N. G. (2004). Structure of shiga toxin type 2 (Stx2) from Escherichia coli O157:H7. The Journal of Biological Chemistry, 279(26), 27511–27517. doi:10.1074/jbc.M401939200</ref>.
-
<scene name='68/687332/B_sub-unit/1'>The B sub-unit (2XSC)</scene> is a symmetrical pentamer that resembles a star and can be divided into five identical monomers. Each monomer is 69 amino acids in length. The purpose of the B sub-unit is to bind to globotriaosylceramide (GB3) which is a glycosphingolipid that is found on the lipid rafts of endothelial cells. Each monomer of the B sub-unit has three binding sites for GB3, binding to the <scene name='68/687332/Gb3_bound_to_sub-unit_b/1'> carbohydrate portion of GB3 (1CQF)</scene>. The affinity between the B sub-unit and GB3 is incredibly low, and is actually one of the lowest recorded affinities for carbohydrate-protein interaction<ref>Jacobson, J. M., Yin, J., Kitov, P. I., Mulvey, G., Griener, T. P., James, M. N. G., … Bundle, D. R. (2014). The crystal structure of Shiga toxin type 2 with bound disaccharide guides the design of a heterobifunctional toxin inhibitor. Journal of Biological Chemistry, 289(2), 885–894. doi:10.1074/jbc.M113.518886</ref>. Some studies have shown that the level of saturation and length of the fatty acid on GB3 affects the strength of its interaction with the B sub-unit. Since the B sub-unit of stx has fifteen binding sites though, it has an incredibly high avidity<ref name="Melton">Melton-Celsa, Angela R. “Shiga Toxin (Stx) Classification, Structure, and Function.” Microbiology spectrum 2.2 (2014): 10.1128/microbiolspec.EHEC–0024–2013. PMC. Web</ref>.
+
<scene name='68/687332/B_subunit/1'>The B sub-unit (2xsc)</scene> is a symmetrical pentamer that resembles a star and can be divided into five identical monomers. Each monomer is 69 amino acids in length. The purpose of the B sub-unit is to bind to globotriaosylceramide (GB3) which is a glycosphingolipid that is found on the lipid rafts of endothelial cells. Each monomer of the B sub-unit has three binding sites for GB3, binding to the <scene name='68/687332/Gb3_bound_to_subunit_b/1'>carbohydrate portion of GB3 (1cqf)</scene>. The B sub-unit has a millimolar affinity for GB3, and is actually one of the lowest recorded affinities for carbohydrate-protein interaction<ref>Jacobson, J. M., Yin, J., Kitov, P. I., Mulvey, G., Griener, T. P., James, M. N. G., … Bundle, D. R. (2014). The crystal structure of Shiga toxin type 2 with bound disaccharide guides the design of a heterobifunctional toxin inhibitor. Journal of Biological Chemistry, 289(2), 885–894. doi:10.1074/jbc.M113.518886</ref>. Some studies have shown that the level of saturation and length of the fatty acid on GB3 affects the strength of its interaction with the B sub-unit. Since the B sub-unit of stx has fifteen binding sites though, it significantly increases the strength of the interaction.<ref name="Melton">Melton-Celsa, Angela R. “Shiga Toxin (Stx) Classification, Structure, and Function.” Microbiology spectrum 2.2 (2014): 10.1128/microbiolspec.EHEC–0024–2013. PMC. Web</ref>.
== Function ==
== Function ==
The pathway of stx entering a cell begins with the B sub-unit’s binding to GB3. Once this occurs, the A sub-unit disconnects from the B sub-unit and enters the cell through endocytosis. Using retrograde transport the A sub-unit passes through the Golgi apparatus and the rough endoplasmic reticulum<ref name="Melton">Melton-Celsa, Angela R. “Shiga Toxin (Stx) Classification, Structure, and Function.” Microbiology spectrum 2.2 (2014): 10.1128/microbiolspec.EHEC–0024–2013. PMC. Web</ref> In the rough endoplasmic reticulum, the A sub-unit is cleaved into two parts, A1 and A2, through the cleavage of trypsin sensitive residues and the reduction of a disulfide bridge. A2 is degraded, but A1 freely enters the cytosol<ref name="Sandvig">Sandvig, K., & van Deurs, B. (2000). Entry of ricin and Shiga toxin into cells: molecular mechanisms and medical perspectives. The EMBO Journal, 19(22), 5943–5950. doi:10.1093/emboj/19.22.5943</ref>. Once in the cytosol, A1 acts as an N-glycosidase, hydrolyzing bonds that link sugars. With this enzymatic activity, A1 removes an adenine from the alpha-sarcin loop in the 28S RNA of the 60S ribosomal sub-unit<ref name="Melton">Melton-Celsa, Angela R. “Shiga Toxin (Stx) Classification, Structure, and Function.” Microbiology spectrum 2.2 (2014): 10.1128/microbiolspec.EHEC–0024–2013. PMC. Web</ref>. The removal of the adenine prevents elongation factors from associating with the ribosomal sub-unit. Without elongation factors, the ribosome can no longer synthesize proteins, leading to cell death<ref name="Melton">Melton-Cesla, A. (2012). Shiga toxin classification structure and function. Changes, 29(2), 997–1003</ref>.
The pathway of stx entering a cell begins with the B sub-unit’s binding to GB3. Once this occurs, the A sub-unit disconnects from the B sub-unit and enters the cell through endocytosis. Using retrograde transport the A sub-unit passes through the Golgi apparatus and the rough endoplasmic reticulum<ref name="Melton">Melton-Celsa, Angela R. “Shiga Toxin (Stx) Classification, Structure, and Function.” Microbiology spectrum 2.2 (2014): 10.1128/microbiolspec.EHEC–0024–2013. PMC. Web</ref> In the rough endoplasmic reticulum, the A sub-unit is cleaved into two parts, A1 and A2, through the cleavage of trypsin sensitive residues and the reduction of a disulfide bridge. A2 is degraded, but A1 freely enters the cytosol<ref name="Sandvig">Sandvig, K., & van Deurs, B. (2000). Entry of ricin and Shiga toxin into cells: molecular mechanisms and medical perspectives. The EMBO Journal, 19(22), 5943–5950. doi:10.1093/emboj/19.22.5943</ref>. Once in the cytosol, A1 acts as an N-glycosidase, hydrolyzing bonds that link sugars. With this enzymatic activity, A1 removes an adenine from the alpha-sarcin loop in the 28S RNA of the 60S ribosomal sub-unit<ref name="Melton">Melton-Celsa, Angela R. “Shiga Toxin (Stx) Classification, Structure, and Function.” Microbiology spectrum 2.2 (2014): 10.1128/microbiolspec.EHEC–0024–2013. PMC. Web</ref>. The removal of the adenine prevents elongation factors from associating with the ribosomal sub-unit. Without elongation factors, the ribosome can no longer synthesize proteins, leading to cell death<ref name="Melton">Melton-Cesla, A. (2012). Shiga toxin classification structure and function. Changes, 29(2), 997–1003</ref>.

Current revision

This Sandbox is Reserved from 15-Jan-2015, through 30-May-2015 for use in the course "Biochemistry" taught by Jason Telford at the Maryville University. This reservation includes Sandbox Reserved 977 through Sandbox Reserved 986.
To get started:
  • Click the edit this page tab at the top. Save the page after each step, then edit it again.
  • Click the 3D button (when editing, above the wikitext box) to insert Jmol.
  • show the Scene authoring tools, create a molecular scene, and save it. Copy the green link into the page.
  • Add a description of your scene. Use the buttons above the wikitext box for bold, italics, links, headlines, etc.

More help: Help:Editing

Shiga Toxin

Crystal Structure for Shiga Toxin (1R4Q)

Drag the structure with the mouse to rotate

References

  1. ↑ 1.0 1.1 Fraser, M. E., Fujinaga, M., Cherney, M. M., Melton-Celsa, A. R., Twiddy, E. M., O’Brien, A. D., & James, M. N. G. (2004). Structure of shiga toxin type 2 (Stx2) from Escherichia coli O157:H7. The Journal of Biological Chemistry, 279(26), 27511–27517. doi:10.1074/jbc.M401939200
  2. ↑ 2.0 2.1 Sandvig, K., & van Deurs, B. (2000). Entry of ricin and Shiga toxin into cells: molecular mechanisms and medical perspectives. The EMBO Journal, 19(22), 5943–5950. doi:10.1093/emboj/19.22.5943
  3. ↑ Jacobson, J. M., Yin, J., Kitov, P. I., Mulvey, G., Griener, T. P., James, M. N. G., … Bundle, D. R. (2014). The crystal structure of Shiga toxin type 2 with bound disaccharide guides the design of a heterobifunctional toxin inhibitor. Journal of Biological Chemistry, 289(2), 885–894. doi:10.1074/jbc.M113.518886
  4. ↑ 4.0 4.1 4.2 4.3 Melton-Celsa, Angela R. “Shiga Toxin (Stx) Classification, Structure, and Function.” Microbiology spectrum 2.2 (2014): 10.1128/microbiolspec.EHEC–0024–2013. PMC. Web
  5. ↑ Zaidi, Mussaret Bano, and Teresa Estrada-García. "Shigella: A Highly Virulent and Elusive pathogen." Current Tropical Medicine Reports 1.2 (2014): 81-87
  6. ↑ Kaper, James B. and Alison D. O’Brien. “Overview and Historical Perspectives.” Microbiology spectrum 2.2 (2014): 10.1128/microbiolspec.EHEC–0028–2014. PMC. Web
  7. ↑ Krüger, Alejandra, and Paula María Alejandra Lucchesi. "Shiga toxins and stx-phages: highly diverse entities." Microbiology (2014): mic-0
Retrieved from "http://52.214.119.220/wiki/index.php/Sandbox_Reserved_982"
Personal tools