Sandbox Reserved 492: Difference between revisions

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OCA, Charlie Zogzas

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 <Structure load='3ki4' size='300' color='white' frame='true' align='right' caption='X-Ray Diffraction image at 2.1Å of Cholix Toxin from Vibrio Cholerae' />
 == Cholix Toxin from ''Vibrio Cholerae ''==
-The [http://en.wikipedia.org/wiki/Crystal_structure crystal structure] of the purified form of ''' Cholix Toxin''' or '''CT''' was determined in 1995. [3] It is an oligomeric bacterial protein found to be made up of six individual <scene name='Sandbox_Reserved_496/Secondary_structure/1'>subunits, </scene> one single α-subunit and 5 individual β- subunits.The α-subunit makes up what is known as the enzymatic portion of the protein while the 5 copies of the β-subunit are responsible for the binding to the ligand receptor. The toxin binds highly specifically and tightly to a [http://en.wikipedia.org/wiki/GM1_gangliosidoses GM1 gangliosides] on the surface of the host's cells. In this X-Ray Diffraction image we can see the <scene name='Sandbox_Reserved_496/Binding_site/1'>catalytic</scene> site, which in this case has been complexed with an allosteric inhibitor (red and yellow space filling atoms). Recent studies have indicated several amino acid <scene name='Sandbox_Reserved_496/Critical_amino_acids/2'> residues </scene> located proximally to the active site which are critical for enzymatic activity. Specifically, site directed mutagenesis indicated that when altered, the mutation results in a termination of the proteins toxicity, rendering it essentially harmless.
+The [http://en.wikipedia.org/wiki/Crystal_structure crystal structure] of the purified form of ''' Cholix Toxin''' or '''CT''' was determined in 1995. <ref>[1] Zhang R, Scott D, Westbrook M, Nance S, Spangler B, Shipley G, Westbrook E (1995). "The three-dimensional crystal structure of cholera toxin". J Mol Biol 251 (4): 563–73. doi:10.1006/jmbi.1995.0456.PMID 7658473.</ref> It is an oligomeric bacterial protein found to be made up of six individual subunits. V. cholerae toxin, along with other similar bacterial enterotoxins seem to share an evolutionary conserved <scene name='Sandbox_Reserved_496/Secondary_structure/1'> secondary structure </scene> composition comprising of about 13 alpha-helices and 10-12 Beta-sheets. The protein is then further divided into one single A-subunit and 5 individual B- subunits.The A-subunit makes up what is known as the enzymatic portion of the protein while the 5 copies of the B-subunit are responsible for the binding to the ligand receptor. The toxin binds highly specifically and tightly to a [http://en.wikipedia.org/wiki/GM1_gangliosidoses GM1 gangliosides] on the surface of the host's cells. In this X-Ray Diffraction image we can see the <scene name='Sandbox_Reserved_496/Binding_site/1'>catalytic</scene> site, which in this case has been complexed with an allosteric inhibitor (red and yellow space filling atoms). Recent studies have indicated several amino acid <scene name='Sandbox_Reserved_496/Critical_amino_acids/2'> residues </scene> located proximally to the active site which are critical for enzymatic activity. Specifically, site directed mutagenesis indicated that when altered, the mutation results in a termination of the proteins toxicity, rendering it essentially harmless.
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 == '''Toxin Mechanism''' ==
-Once secreted, the B subunit will bind to GM1 gangliosides on the surface. After ''binding'' takes place, the whole complex is engulfed by the cell and a portion known as the CTA1 chain is detached after reduction of a disulfide bridge. The new endosome is moved to the Golgi, where it is recognized by the endoplasmic reticulum, unfolded and delivered to the membrane, where the Endoplasmic Reticulum-oxidase - "'''Ero1'''" triggers the release of the excised A1 protein (through Oxidation) of '''protein disulfide isomerase complex'''. As A1 moves from the ER into the cytoplasm it refolds and avoids further reduction.[1]
+Once secreted, the B subunit will bind to GM1 gangliosides on the surface. After ''binding'' takes place, the whole complex is engulfed by the cell and a portion known as the CTA1 chain is detached after reduction of a disulfide bridge. The new endosome is moved to the Golgi, where it is recognized by the endoplasmic reticulum, unfolded and delivered to the membrane, where the Endoplasmic Reticulum-oxidase - "'''Ero1'''" triggers the release of the excised A1 protein (through Oxidation) of '''protein disulfide isomerase complex'''. As A1 moves from the ER into the cytoplasm it refolds and avoids further reduction. <ref> [2] O'Neal C, Jobling M, Holmes R, Hol W (2005). "Structural basis for the activation of cholera toxin by human ARF6-GTP". Science 309 (5737): 1093–6. doi:10.1126/science.1113398. PMID 16099990. </ref>
-The A1 fragment catalyses '''ADP ribosylation''' from NAD to the regulatory component (G-protein) of adenylate cyclase, two main components in an important signal transduction pathway. The newly formed A1-Gαs complex is then unable to hydrolyse properly leaving the GTP bound to the Gαs subunit, which results in the transducer being continually activated. Increased adenylate cyclase activity increases cyclic AMP (cAMP concentration increases more than 100 times normal concentrations) synthesis. This can cause rapid fluid loss from the intestines, up to 2 liters per hour, leading to severe dehydration and diarrhea.
-[[Image:Cholera_Mechanism.jpg]]
+The A1 fragment catalyses '''ADP ribosylation''' from NAD to the regulatory component (G-protein) of adenylate cyclase, two main components in an important signal transduction pathway. The newly formed A1-Gαs complex is then unable to hydrolyse properly leaving the GTP bound to the Gαs subunit, which results in the transducer being continually activated. Increased adenylate cyclase activity increases cyclic AMP (cAMP concentration increases more than 100 times normal concentrations) synthesis. This can cause rapid fluid loss from the intestines, up to 2 liters per hour,<ref> [3] Joaquín Sánchez, Jan Holmgren (February 2011). [icmr.nic.in/ijmr/2011/february/0204.pdf "Cholera toxin – A foe & a friend"]. Indian Journal of Medical Research 133: p. 158. </ref>leading to severe dehydration and diarrhea.
+[[Image:Cholera_Mechanism.jpg]] <ref>[4]http://www.ebi.ac.uk/interpro/potm/2005_9/Page2.htm</ref>
+''Diagram of proposed mechanism for CX intoxication''
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+== '''Studies & Potential Benefits''' ==
+While CX intoxication from the bacterium is an incredibly serious and even life-threatening condition, tests conducted have shown that the toxin can be directly inhibited on the molecular level. The catalytic subunit of the CX protein is known to bind, with high affinity, to a molecule known as PJ34<ref>[5]Jørgensen, R, A E. Purdy, R J. Fieldhouse, D H. Bartless, and A R. Merrill. “Cholix toxin, a novel ADP-ribosylating factor from Vibrio cholerae..” Journal of Biological Chemistry 8, (2008)</ref> - as well as with other structurally conserved, fused-hydrocarbon ring inhibitors. These types of interactions are studied through the use of computerized modeling, where factors such as Van der Waal radii, atomic radii, electron affinity etc.. are assessed producing viable molecular model.
+                                          <Structure load='2Q6M' size='425' color='black' frame='true' align='left' caption='X-Ray Diffraction image at 2.1Å of catalytic fragment with PJ34 inhibitor bound.' /> [[Image:P34.PNG] align='right']
+Essentially, the <scene name='Sandbox_Reserved_492/Pj34_inhibitor/1'>PJ34</scene>replaces what would be the target protein in the epithelial cell of a human thus prevents the Cholera Toxin from interacting with its normal ligand; this would in turn prevent the ill effects of intoxication...in theory.
+Cholix also serves several valuable purposes in Biological research. Dr. Pierre-Hervé Luppi and his laboratory recently discovered a new "tracing" method using cholera-toxin instead of the previously used classical molecules such as Horse Radish Peroxidase (HRP). In contrast to HRP, which is '''passively''' taken up by neurons, cholera-toxin (as we discussed previously) binds specifically to surface receptors of neurons and is can be '''actively''' taken up and transported by the axons. <ref> [6] Pierre-Hervé Luppi. "The Discovery of Cholera-Toxin as a Powerful Neuroanatomical Tool". Retrieved 2011-03-23. </ref> This phenomenon helps enhance the sensitivity of cholera-toxin as a tracer, for studies dealing with neural function and the diseases known to affect it.                                                                         [[Image:P34.png]] ''Structure of '''PJ34'''''
+{{clear}}
-== '''Uses & Potential Benefits''' ==
+As a result, aspirations for future research being done on Cholera Toxin today, coincide with a current "hot topic" within the science community and the entre World: '''Stem Cell Research.''' There have been some recent findings indicating that the protein may be capable of interacting - regulation on the genetic level - some key factors in Neural Stem Cell '''(NSC)''' regeneration and differentiation. Known as Tie2, a membrane receptor, and Hes3 a transcription factor, these two indicators have been shown to directly interact with the Cholix Toxin. Moreover, there are even some implications that the protein, when combined with specific medium, boosted Stem Cell culture growth.<ref>[7]Androutsellis-Theotokis, Andreas, Stuart Walbridge, Deric M. Park, Russel R. Lonser, and Ronald D. McKay. “Cholera Toxin Regulates a Signaling Pathway Critical for the Expansion of Neural Stem Cell Cultures from the Fetal and Adult Rodent Brains.” PLoS ONE 5, (2010)</ref> Thus, we see that apart from its potential to cause human illness, CX also poses a solution to cancer and other related diseases.      [[Image:NSC.jpeg]]
-While measures of treating someone with CX intoxication generally involves carefully replenishing electrolytes and other vital fluids there have been plenty of tests conducted that show that the toxin can be directly inhibited on the molecular level as well. The catalytic subunit of the CX protein has shown to bind, with high affinity a molecule known as PJ34- as well as other structurally conserved, fused-hydrocarbon ring inhibitors. Essentially, the PJ34 replaces what would target protein in the epithelial cell of a human host and prevent the ill effects of intoxication...in theory.
-<Structure load='2q6m' size='425' color='black' frame='true' align='middle' caption='X-Ray Diffraction image at 2.1Å of catalytic fragment with PJ34 inhibitor bound.' />
-An aspiration for research being done on the Cholera Toxin coincides with a current "hot topic" within the science community and society around the world: '''Stem Cell Research.''' There have been some recent findings indicating that the protein may be capable of interacting - regulation on the genetic level - some key factors in Neural Stem Cell '''(NSC)''' regeneration and differentiation. Known as Tie2, a membrane receptor, and Hes3 a transcription factor, these two indicators have been shown to directly interact with the Cholix Toxin. Moreover, there are even some implications that the protein, when combined with specific medium, boosted Stem Cell culture growth.[5] Thus, we see that apart from its potential to cause human illness, CX also poses the potential to offer a solution to cancer and other related diseases.
+==References ==
+<references/>