High-potential iron proteins residues

By any sort of definition, turns are an important feature of protein structure. Kuntz (1972) found 45% of protein backbone in turns or loops Chou and Fasman (1977) found 32% of protein chain in turns (counting four residues per turn) and Zimmerman and Scheraga (1977b) found 24% of the nonhelical residues in turns (counting only the central dipeptide). There are also some particular proteins whose structure appears heavily dependent on turns Fig. 38 shows high-potential iron protein (Carter et ah, 1974), with the 17 turns in 85 residues indicated and their location at the surface evident. 

High-potential iron proteins, 45 313-314, 344 cluster stability, 45 324-332 function, 45 315-316 residues, 45 322-344 structure and, 45 317-322 redox properties, 45 333-344 solvent accessibility, 45 330, 332-333 source and function, 45 314-316 structure, 45 316-322 hydrogen bonding and, 45 321-322 intermolecular aggregation, 45 322 primary, 45 317-318 secondary and tertiary, 45 318-321... 

Several models have been proposed for the active center of iron and sulphur in Clostridial ferredoxin in which the cysteine residues in the peptide chain participate in the sulphur bridging. Fig 9 166). Unfortunately X-ray analysis of crystals of these proteins has not been completed. It is difficult to confirm that all the irons are clustered in a single linear array 167, 168). X-ray studies of another non-heme iron protein, the high potential iron protein, hipip, from chromatium, carried out by J. Kraut (personal communication), indicate that the four irons of this molecule may be clustered in a tetrahedral array. 

Another group of related electron carriers, the high-potential iron proteins (HIPIP) contain four labile sulfur and four iron atoms per peptide chain 261-266 X-ray studies showed that the 86-residue polypeptide chain of the HIPIP of Chromatium is wrapped around a single iron-sulfur cluster which contains the side chains of four cysteine residues plus the four iron and four sulfur atoms (Fig. 16-15D)261 This kind of cluster is referred to as [4Fe-4S], or as Fe4S4. Each cysteine sulfur is attached to one atom of Fe, with the four iron atoms forming an irregular tetrahedron with an Fe-Fe... 

Figure 17. Schematic diagrams of some representative topologically chiral proteins.79 (a) Condensed schematic drawing of the L subunit of the quinoprotein TV-MADH. The looped line represents the polypeptide backbone with N and C terminals. Cysteine (or half-cystine) residues are numbered, and their a-carbons are indicated by filled circles. Intrachain disulfide bonds are shown as dashed lines joining a pair of filled circles. The heavy line symbolizes an intrachain cofactor link, (b) Chromatium high potential iron protein (HiPIP), one of several Fe4S4 cluster-containing proteins, (c) Toxin II from the scorpion Androctonus australis Hector. Reprinted with permission from C. Liang and K. Mislow, J. Math. Chem. 1994,15,245. Copyright 1994, Baltzer Science Publishers.

High-potential Iron Proteins. These proteins (HiPIP s) have redox potentials some 0.7 V more positive than those of the ferredoxins. Chromatium HiPIP, the best characterized one, has a molecular weight of about 10,000, contains four iron atoms, four atoms of inorganic sulfur and four cysteine residues. X-ray investigation34 has shown that the iron and sulfur atoms form the tetrahedral array (Fig. 25-E-3). 

Fluorine-labeled analogues of C. vinosum high-potential iron protein have been investigated by F NMR spectroscopy. By incorporation of specific fluorine-labeled amino acid residues, one can insert unique probes at well-defined locations within the protein core. The synthesis and purification of 2-, 3-, and 4-fluorophenylalanine (abbreviated 2-F-, 3-F-, and 4-F-Phe, respectively), 3-fluorotyrosine (3-F-Tyr), and 5-fluorotr3q)tophan (5-F-Trp) derivatives of C. vinosum HiPIP, the assignment of F NMR resonances, the measurement of longitudinal relaxation times, and the temperature dependence of F and resonances have all been reported 42, 43, 136). These measurements were used to examine structural perturbations of mutants, the dynamics of interaction of residues with the cluster, and solvent accessibility, and as a test of the relative contribution of cross-relaxation to magnetization decay. 

Iron-sulfur proteins occur in animal, plant, and bacterial cells. The proteins are characterized by the presence of 1-0, 2-2, 4rA, 6-6, or 8-8 atoms of iroursulfide. Only the structure of clostridial rubredoxin, a 1-0 protein, is knoum. It contains iron ligated to four sulfur atoms of cysteine residues of the polypeptide. With the exception of the ""high potential iron protein, all the proteins show unexpectedly low redox potentials and function in biological oxidationr-reduc-tion reactions. 

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