Aconitase, crystal structure

The X-ray structures of other aconitases have appeared in the literature. Recently, the crystal structure of human iron regulatory protein, IRPl, in its aconitase form, has been published. Iron regulatory proteins (IRPs) control the translation of proteins involved in iron uptake, storage, and utilization by binding to specific noncoding sequences of the corresponding mRNAs known... 

Furthennore, resonance Raman studies of aconitase by Johnson et al. (53) demonstrated homologous spectra for both inactive and active aconitase. This suggests similar vibrational modes and thus similar core structures for the two forms. Finally, a cubane structure for the [3Fe-4S] cluster is supported by recent protein crystallographic studies of inactive aconitase by Robbins and Stout (54). (Recent results from Jensen s group (55) on the redetermination of the crystal structure of the Azotobacter ferredoxin I clearly show that the 3Fe cluster does not have a [3Fe-3S] ring structure, as originally determined (37), but has a [3Fe-4S] cubane structure.)... 

Lauble H, Kennedy MC, Emptage MH, et al. The reaction of fluorocitrate with aconitase and the crystal structure of the enzyme inhibitor complex. Proc Natl Acad Sci U S A 1996 93 13699-13703. 

Aconitase was the first protein to be identified as containing a catalytic iron-sulfur cluster [24-26]. It was also readily established that the redox properties of the [4Fe-4S](2+ 1+) cluster do not play a role of significance in biological functioning the 1 + oxidation state has some 30% of the activity of the 2+ state [25], Since then several other enzymes have been identified or proposed to be nonredox iron-sulfur catalysts. They are listed in Table 2. It appears that all are involved in stereospecific hydration reactions. However, these proteins are considerably less well characterized than aconitase. In particular, no crystal structural information is available yet. Therefore, later we summarize structural and mechanistic information on aconitase, noting that many of the basic principles are expected to be relevant to the other enzymes of Table 2. 

X-ray crystal structures are available for cubane-type [3Fe-4S] centers in 3Fe and 7Fe Fds, aconitase, NiFe-hydrogenases, succinate dehydrogenase, fumarate... 

Lauble, H., Kennedy, M.C., Beinert, H., Stout, C.D. (1992). Crystal structures of aconitase with isocitrate and nitro-isocitrate bound. Biochemistry 38 2735-48. 

S. J. Lloyd, H. Lauble, G.S. Prasad, and C.D. Stout. 1999. The mechanism of aconitase 1.8 A resolution crystal structure of the S642a citrate complex. Protein Sci. 8 2655-2662. (PubMed)... 

A comparable picture emerges for pig heart aconitase from the work of Robbins and Stout (115), who have determined the crystal structures of the inactive and active forms. These forms are isomorphous. The seven Fe and S atoms common to the cores of the two clusters differ in position by only 0.11 A on average, and the three common cysteinyl sulfur atoms differ by 0.25 A. 

A number of 4-Fe-containing proteins readily lose one of the Fe atoms to form a 3-Fe protein. An early crystal structure of ferrodoxin I from Azotobacter vinelandii was interpreted as showing a planar Fe3S3 ring for the 3-Fe cluster. This interpretation was shown to be inconsistent with the RR spectrum, via a normal coordinate analysis and by comparison with the spectral pattern of a planar model compound, (CH3)3Sn3S3. The crystal structure was subsequently corrected to reveal a Fe3S4 cube with a missing corner.The same structure has been determined for the inactive form of the enzyme aconitase, and the similarity of the... 

Fig. 5.3. Protein structure determination by X-ray diffraction. A. Crystals of porcine heart aconitase composed of 754 amino acids. The orthorhombic crystals shown are about 0.5 mm in the longest dimension. B. Film showing the diffraction pattern obtained from the above crystal. These data were used to obtain a 2.7 A resolution structure shown in two representations in panels C and D. Panel C shows the tracing of the protein backbone, with the small molecule (in red and yellow) in the central region depicting the iron-containing cofactor of the enzyme. Panel D shows the space-filling representation. (Courtesy of Dr Arthur H. Robbins, Miles Pharmaceuticals Inc. For details see A.H.Robbins and C.D.Stout (1989). Proteins Structure, Function, and Genetics 5, 289 312.)...

Taylor, B. Methodus Incrementorum Directa et Inversa. Proposition 7. [Direct and indirect methods of incrementation.] Peajsniansis Londini (1715) dusker, J. P., Orehowsky, W. Jr., Casciato, C. A., and Carrell, H. L. X-ray crystal analysis of the substrates of aconitase. X. The structure of dipotassium ds-aconitate. Acta Cryst. B28, 419-425 (1972). 

Normal coordinate calculations by Johnson et al. have shown that the RR spectra of AuFdl crystals and 3Fe bacterial ferredoxins (Cp Fd and Tt Fd) are compatible with cubanelike 3Fe-4S structures proposed by Beinert el al. but not with the 3Fe-3S ring structure found for Av Fd 1. The RR spectra of aconitase and Desuljovibrio desulfuricans are also very similar to those mentioned above, indicating the possibility o " the cubanelike 3Fe-4S structures in these proteins. 

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