Diiron proteins

Table 2.4 Some properties of diiron proteins. From Kurz, 1997. Reproduced by permission of Springer-Verlag. 

Iron is stored in these proteins in the ferric form, but is taken up as Fe2+, which is oxidized by ferroxidase sites (a more detailed account of iron incorporation into ferritins is given later in this chapter). As we point out in Chapter 13, ferritins are members of the much larger diiron protein family. After oxidation, the Fe3+ migrates to the interior cavity of the protein to form an amorphous ferric phosphate core. Whereas the ferritins in bacteria appear to fulfil the classical role of iron-storage proteins, the physiological role of bacterioferritins is less clear. In E. coli it seems unlikely that bacterioferritin plays a major role in iron storage. 

Figure 13.25 Three-dimensional structures of diiron proteins. The iron-binding subunits of (a) haemery-thrin, (b) bacterioferritin, (c) rubryerythrin (the FeS centre is on the top), (d) ribonucleotide reductase R2 subunit, (e) stearoyl-acyl carrier protein A9 desaturase, (f) methane monooxygenase hydroxylase a-subunit. (From Nordlund and Eklund, 1995. Copyright 1995, with permission from Elsevier.)...

Rees, D.C. (2002) Great metalloclusters in enzymology, Anna. Rev. Biochem., 71, 221-246. Sazinsky, M.H. and Lippard, S.J. (2006) Correlating structure with function in bacterial multicomponent monooxygenases and related diiron proteins, Acc. Chem. Res., 39, 558-566. 

Many aminopeptidases are metalloenzymes.437 Most studied is the cytosolic leucine aminopeptidase which acts rapidly on N-terminal leucine and removes other amino acids more slowly. Each of the subunits of the hexameric enzyme contains two divalent metal ions, one of which must be Zn2+ or Co2+438/439 A methionine aminopeptidase from E. colt contains two Co2+ ions440/441 and a proline-specific aminopeptidase from the same bacterium two Mn2+.442 In all of these enzymes the metal ions are present as dimetal pairs similar to those observed in phosphatases and discussed in Section D,4 and to the Fe-Fe pairs of hemerythrin and other diiron proteins (Fig. 16-20). A hydroxide ion that bridges the metal ions may serve as the nucleophile in the aminopeptidases.438 A bound bicarbonate ion may assist.4383... 

Dihydroxyproline 80 Diiron desaturases 863 Diiron oxygenases 863 Diiron proteins 862-864 Diiron-tyrosinate proteins 862-863 Diisopropylfluorophosphate (DFP, diisopropylphosphofluoridate) 610s Dimethylallyl diphosphate 712s Dimethylallyl pyrophosphate, condensation of 527... 

Noncompetitive inhibition 476,477 Nonheme iron proteins. See Iron-sulfur and diiron proteins Nonlinear equations 460 Nonmetallic ions, ionic radii, table 310 Nonproductive complexes 475 Norepinephrine (noradrenaline) 553,553s in receptor 555s Nuclear envelope 11... 

Moenne-Loccoz, P., Krebs, C., Herlihy, K., Edmondson, D. E., Theil, E. C., Huynh, B. H., and Loehr, T., 1999, The ferroxidase reaction of ferritin reveals a diferric p-1,2 bridging peroxide intermediate in common with other 02-activating non-heme diiron proteins,... 

Logan, D. T, deMarE, F., Persson, B. O., Slaby, A., Sj berg, B.-M., and Nordlund, P., 1998, Crystal structures of two self-hydroxylating ribonucleotide reductase protein R2 mutants Structural basis for the oxygen-insertion step of hydroxylation reactions catalyzed by diiron proteins. Biochemistry 37 10798nl0807. 

Fig. 40. The active sites of some /x-oxo-diiron proteins, hemerythrin (top), ribonucleo-...

Lee M, Lenman M, Banas A, Bafor M, Singh S, Schweizer M, Nilsson R, Liljenberg C, Dahlqvist A, Gununeson P-O, Sjodahl S, Green A, Stynuie S. Identification of nonheme diiron proteins... 

A. Magistrate, W. DeGrado, U. RothUsberger, and M. Klein (2003) Structural and Dynamical Characterization of Dizinc DPI, a Biomimetic Compound of Diiron Proteins via ab initio and Hybrid (QM/MM) Molecular Dynamics. J. Phys. Chem. B 107, p. 4182... 

II. DIIRON PROTEINS THAT INTERACT WITH DIOXYGEN.99... 

DINUCLEAR IRON- AND MANGANESE-OXO SITES IN BIOLOGY 99 II. DIIRON PROTEINS THAT INTERACT WITH DIOXYGEN... 

Figure 8. Fourier-filtered first shell EXAFS data for several diiron proteins. Reprinted with permission from L. Oue, Jr., R. C. Scarrow, in Metal Clusters in Proteins, L. Que, Jr., Ed., American Chemical Society, Washington, DC, 1988, pp, LS2-178. Copyright (1988) American Chemical Society.

Figure 14, EPR spectra of mixed-valence forms of the diiron proteins (a) semimetuHr, (6) semimetoHr, (c) Uf, (d) Uf,-Mo04, (e) bovine spleen PAP, (/) MMO ,. Reprinted with permission from Ref. 6. Copyright 1987 Elsevier.

Although they show little overall sequence identity, the dinuclear centers of the three prototype ferritins, particularly that of EcBfr, are remarkably similar in both amino acid residues and their geometry to those of the class 2 diiron proteins that comprises the ribonucleotide reductase R2 subunit (RNR R2), the methane monooxygenase hydroxylase component (MMOH), rubrerythrin (Rr) and several other... 

H-type ferritins belong to the class II diiron proteins that also comprises RNR R2 and MMOH subunits, ACP-stearoyl-desaturase and rubrerythrin. Interaction of... 

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