Haem, structure

The table lists the number of contacting globin-haem atom pairs at each position for which at least one of the six haem structures makes a potential contact. All interatomic distances less than 4.2 A are counted as potential contacts (see legend to Fig.4 for details). The haem iron and ligated oxygen are excluded from contact counts. 

The structure of the diamagnetic, cherry-red vitamin B12 is shown in Fig. 26.6 and it can be seen that the coordination sphere of the cobalt has many similarities with that of iron in haem (see Fig. 25.7). In both cases the metal is coordinated to 4 nitrogen atoms of an unsaturated macrocycle (in this case part of a corrin ring which is less symmetrical and not so unsaturated as the porphyrin in haem) with an imidazole nitrogen in the fifth position. A major... 

Blasiak, L.G., Vaillancourt, F.H., Walsh, C.T. and Drennan, C.L. (2006) Crystal structure of the non-haem iron halogenase SyrB2 in syringomycin biosynthesis. Nature, 440, 368-371. 

There are two types of electron transport those involving flavoproteins and iron-sulfur proteins, and those requiring only flavoproteins. The X-ray crystal structure of the soluble cytochrome P450 from Pseudomonas putida grown on camphor (P-450-CAM) has been determined (Poulos et ah, 1985), as have several others. The haem group is deeply embedded in the hydrophobic interior of the protein, and the identity of the proximal haem iron ligand, based on earlier spectroscopic studies (Mason et ah, 1965) is confirmed as a specific cysteine residue. 

Figure 2.6 Chemical structures (a) and axial ligands (b) to the haem groups in cytochromes a, b and c. From Voet and Voet, 1995. Reproduced by permission of John Wiley Sons, Inc.

One last class of mononuclear non-haem iron enzyme that we have not yet considered, consists of the microbial superoxide dismutases with Fe(III) at their active site. The crystal structure of the E. coli enzyme shows a coordination geometry reminiscent of protocatechuate 3,4-dioxygenase, with four endogenous protein ligands, three His and one Asp residue, and one bound water molecule (Carlioz et ah, 1988). 

FhuA and FepA will prove to be the reference structures for a large group of bacterial outer-membrane transporters that take up bacterial Fe3+-siderophores, Fe3+ released from host transferrin and lactoferrin, haem, and haem released from haemoglobin and haemopexin. It is assumed that all iron sources are transported... 

Figure 4.2 Hypothetical plasma membrane (PM)-associated structure of FR02. Four histidine residues (white spots) predicted to coordinate two intramembraneous haem groups (white bars) are indicated, as are the tetrapeptide binding sites for FAD and N AD(P)H. The sites of mutations in the FRO gene are indicated (frdl-l,frdl-3) i, inside cell o, outside cell. Reprinted with permission from Nature (Robinson et al., 1999). Copyright (1999) Macmillan Magazines Limited.

The detailed high-resolution structure of the non-haem-containing ferritin of E. coli EcFTNA has been recently published (Stillman et al, 2000) and shows considerable structural similarity to human H-chain ferritin (r.m.s. deviation of main chain... 

Rubrerythrin is the trivial name given to a family of non-haem iron proteins that have been isolated from a number of bacteria (Figure 6.2). The structure of the best characterized rubrerythrin, that from Desulfovibrio vulgaris, has been determined by... 

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