1x0k: Difference between revisions
New page: left|200px<br /><applet load="1x0k" size="450" color="white" frame="true" align="right" spinBox="true" caption="1x0k, resolution 2.60Å" /> '''Crystal Structure of... |
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[[Image:1x0k.gif|left|200px]]<br /><applet load="1x0k" size=" | [[Image:1x0k.gif|left|200px]]<br /><applet load="1x0k" size="350" color="white" frame="true" align="right" spinBox="true" | ||
caption="1x0k, resolution 2.60Å" /> | caption="1x0k, resolution 2.60Å" /> | ||
'''Crystal Structure of Bacteriorhodopsin at pH 10'''<br /> | '''Crystal Structure of Bacteriorhodopsin at pH 10'''<br /> | ||
==Overview== | ==Overview== | ||
Bacteriorhodopsin, a light-driven proton pump found in the purple membrane | Bacteriorhodopsin, a light-driven proton pump found in the purple membrane of Halobacterium salinarum, exhibits purple at neutral pH but its color is sensitive to pH. Here, structures are reported for an acid blue form and an alkaline purple form of wild-type bacteriorhodopsin. When the P622 crystal prepared at pH 5.2 was acidified with sulfuric acid, its color turned to blue with a pKa of 3.5 and a Hill coefficient of 2. Diffraction data at pH 2-5 indicated that the purple-to-blue transition accompanies a large structural change in the proton release channel; i.e. the extracellular half of helix C moves towards helix G, narrowing the proton release channel and expelling a water molecule from a micro-cavity in the vicinity of the retinal Schiff base. In this respect, the acid-induced structural change resembles the structural change observed upon formation of the M intermediate. But, the acid blue form contains a sulfate ion in a site(s) near Arg82 that is created by re-orientations of the carboxyl groups of Glu194 and Glu204, residues comprising the proton release complex. This result suggests that proton uptake by the proton release complex evokes the anion binding, which in turn induces protonation of Asp85, a key residue regulating the absorption spectrum of the chromophore. Interestingly, a pronounced structural change in the proton release complex was also observed at high pH; i.e. re-orientation of Glu194 towards Tyr83 was found to take place at around pH 10. This alkaline transition is suggested to be accompanied by proton release from the proton release complex and responsible for rapid formation of the M intermediate at high pH. | ||
==About this Structure== | ==About this Structure== | ||
1X0K is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Halobacterium_salinarum Halobacterium salinarum] with RET, L3P and L2P as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http:// | 1X0K is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Halobacterium_salinarum Halobacterium salinarum] with <scene name='pdbligand=RET:'>RET</scene>, <scene name='pdbligand=L3P:'>L3P</scene> and <scene name='pdbligand=L2P:'>L2P</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1X0K OCA]. | ||
==Reference== | ==Reference== | ||
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[[Category: membrane protein]] | [[Category: membrane protein]] | ||
''Page seeded by [http:// | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 15:49:55 2008'' | ||
Revision as of 16:49, 21 February 2008
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Crystal Structure of Bacteriorhodopsin at pH 10
OverviewOverview
Bacteriorhodopsin, a light-driven proton pump found in the purple membrane of Halobacterium salinarum, exhibits purple at neutral pH but its color is sensitive to pH. Here, structures are reported for an acid blue form and an alkaline purple form of wild-type bacteriorhodopsin. When the P622 crystal prepared at pH 5.2 was acidified with sulfuric acid, its color turned to blue with a pKa of 3.5 and a Hill coefficient of 2. Diffraction data at pH 2-5 indicated that the purple-to-blue transition accompanies a large structural change in the proton release channel; i.e. the extracellular half of helix C moves towards helix G, narrowing the proton release channel and expelling a water molecule from a micro-cavity in the vicinity of the retinal Schiff base. In this respect, the acid-induced structural change resembles the structural change observed upon formation of the M intermediate. But, the acid blue form contains a sulfate ion in a site(s) near Arg82 that is created by re-orientations of the carboxyl groups of Glu194 and Glu204, residues comprising the proton release complex. This result suggests that proton uptake by the proton release complex evokes the anion binding, which in turn induces protonation of Asp85, a key residue regulating the absorption spectrum of the chromophore. Interestingly, a pronounced structural change in the proton release complex was also observed at high pH; i.e. re-orientation of Glu194 towards Tyr83 was found to take place at around pH 10. This alkaline transition is suggested to be accompanied by proton release from the proton release complex and responsible for rapid formation of the M intermediate at high pH.
About this StructureAbout this Structure
1X0K is a Single protein structure of sequence from Halobacterium salinarum with , and as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Crystal structures of acid blue and alkaline purple forms of bacteriorhodopsin., Okumura H, Murakami M, Kouyama T, J Mol Biol. 2005 Aug 19;351(3):481-95. PMID:16023672
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