Aconitase: Difference between revisions
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== Catalytic mechanism of mitochondrial ACO == | == Catalytic mechanism of mitochondrial ACO == | ||
<applet load=7acn scene='Aconitase/7acn-sf4/1' size='400' frame='true' align='left' caption="Mitochondrial aconitase from pig, PDB [[7acn]]." />Both mAc and cAc are quite similar in their ACO function. Studies, however, concentrated on <scene name='Aconitase/7acn-sf4/1'>the mitochondrial ACO</scene>. ACO is an excellent system for understanding the role of iron-sulfur-clusters in catalysis. The <scene name='Aconitase/7acn-sf4-3cys/1'>(4Fe-4S) cofactor is held in place</scene> by three sulfur atoms belonging to the cysteins-385, -448, and -451 <scene name='Aconitase/7acn-sf4-3cys-solo/1'>which are bound to three of the four</scene> cluster iron atoms. The fourth, Fe4, is free to bind; it can be four-, five-, or six-coordinate, but is constrained to bond to three sulfur atoms of the (4Fe-4S)-cluster with | <applet load=7acn scene='Aconitase/7acn-sf4/1' size='400' frame='true' align='left' caption="Mitochondrial aconitase from pig, PDB [[7acn]]." />Both mAc and cAc are quite similar in their ACO function. Studies, however, concentrated on <scene name='Aconitase/7acn-sf4/1'>the mitochondrial ACO</scene>. ACO is an excellent system for understanding the role of iron-sulfur-clusters in catalysis. The <scene name='Aconitase/7acn-sf4-3cys/1'>(4Fe-4S) cofactor is held in place</scene> by three sulfur atoms belonging to the cysteins-385, -448, and -451 <scene name='Aconitase/7acn-sf4-3cys-solo/1'>which are bound to three of the four</scene> cluster iron atoms. The fourth, Fe4, is free to bind; it can be four-, five-, or six-coordinate, but is constrained to bond to three sulfur atoms of the (4Fe-4S)-cluster with tetrahedral geometry. Thus, Fe4 is free to bind one, two, or three partners, in this reaction always oxygen atoms belonging to other molecules. As Fe4 is not bound very fast to the cluster, it moves quite a bit around in the process of bonding and debonding.<ref>PMID:8151704</ref> | ||
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*[[8acn]] - mAc (''Sus scrofa'') with nitroisocitrate | *[[8acn]] - mAc (''Sus scrofa'') with nitroisocitrate | ||
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== | == References == | ||
<references /> | |||
== External links == | |||
*[http://pdb.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/pdb89_1.html Molecule of the Month: Aconitase and Iron Regulatory Protein 1] | *[http://pdb.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/pdb89_1.html Molecule of the Month: Aconitase and Iron Regulatory Protein 1] | ||
*[http://en.wikipedia.org/wiki/Aconitase Aconitase at Wikipedia] | *[http://en.wikipedia.org/wiki/Aconitase Aconitase at Wikipedia] | ||
Revision as of 17:04, 20 February 2009
Aconitase (ACO) is an enzymatic domain that confers the ability to catalyse the equilibrium
- citrate = aconitate + H2O = L-isocitrate
This reaction is part of the citrate (TCA-, Krebs-)cycle.
In most organims, there is a cytosolic enzyme with an ACO domain (cAc), and in eukaryotes, a second copy of it was introduced with mitochondria (mAc). Plants developed even more copies in mitochondria.
Catalytic mechanism of mitochondrial ACO
|
Both mAc and cAc are quite similar in their ACO function. Studies, however, concentrated on the mitochondrial ACO. ACO is an excellent system for understanding the role of iron-sulfur-clusters in catalysis. The (4Fe-4S) cofactor is held in place by three sulfur atoms belonging to the cysteins-385, -448, and -451 which are bound to three of the four cluster iron atoms. The fourth, Fe4, is free to bind; it can be four-, five-, or six-coordinate, but is constrained to bond to three sulfur atoms of the (4Fe-4S)-cluster with tetrahedral geometry. Thus, Fe4 is free to bind one, two, or three partners, in this reaction always oxygen atoms belonging to other molecules. As Fe4 is not bound very fast to the cluster, it moves quite a bit around in the process of bonding and debonding.[1]
Cytosolic aconitase and its other function
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A specialty of cAc is that in mammals it has developed a second function as inhibitor of those mRNA that carry an iron-responsive element (IRE). Therefore, the cytosolic cAc is named IREBP for IRE-binding protein when this function is talked about. Only one of the two functions is active, depending on whether the (4Fe-4S) cofactor is present in the molecule: it's essential for the ACO function. You can see, by looking at the morph, how much the enzyme structure differs between those two functions.
References
- ↑ Lauble H, Kennedy MC, Beinert H, Stout CD. Crystal structures of aconitase with trans-aconitate and nitrocitrate bound. J Mol Biol. 1994 Apr 8;237(4):437-51. PMID:8151704 doi:https://dx.doi.org/10.1006/jmbi.1994.1246
External links
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