Aconitase

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(→Catalytic mechanism of mitochondrial ACO)
(→Catalytic mechanism of mitochondrial ACO)
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== Catalytic mechanism of mitochondrial ACO ==
== Catalytic mechanism of mitochondrial ACO ==
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<applet load=7acn scene='Aconitase/7acn-sf4/1' size='400' frame='true' align='left' caption="Mitochondrial aconitase from pig, PDB [[7acn]]." />The bulk of citrate cycle processing happens in mitochondria and so, studies concentrated on <scene name='Aconitase/7acn-sf4/1'>the mitochondrial ACO</scene>. 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.
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<applet load=7acn scene='Aconitase/7acn-sf4/1' size='400' frame='true' align='left' caption="Mitochondrial aconitase from pig, PDB [[7acn]]." />The bulk of citrate cycle processing happens in mitochondria and so, studies concentrated on <scene name='Aconitase/7acn-sf4/1'>the mitochondrial ACO</scene>. 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 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 terahedral 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.
<!--It is clear that, in order to synthesize L-isocitrate, stereoselective catalysis must occur.-->
<!--It is clear that, in order to synthesize L-isocitrate, stereoselective catalysis must occur.-->

Revision as of 16:18, 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

Mitochondrial aconitase from pig, PDB 7acn.

Drag the structure with the mouse to rotate
The bulk of citrate cycle processing happens in mitochondria and so, studies concentrated on . The 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 terahedral 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.


Cytosolic aconitase and its other function

Cytosolic aconitase from rabbit (bound to RNA) and human (with Fe4S4 cluster), from PDB 2ipy and 2b3x.

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A specialty of cAc is that in mammals it has developed a as inhibitor of that carry an . 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 is present in the molecule: it's essential for . You can see, by , how much the enzyme structure differs between those two functions.

Weblinks

Retrieved from "http://52.214.119.220/wiki/index.php/Aconitase"
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