Tetraheme cytochrome

Myers CR, ID Myers (1997) Cloning and sequence of cymA, a gene encoding a tetraheme cytochrome c required for reduction of iron (III), fumarate, and nitrate by Shewanella putrefaciens MR-1. J Bacteriol 179 1143-1152. 

For the cytochrome c-plastocyanin complex, the kinetic effects of cross-linking are much more drastic while the rate of the intracomplex transfer is equal to 1000 s in the noncovalent complex where the iron-to-copper distance is expected to be about 18 A, it is estimated to be lower than 0.2 s in the corresponding covalent complex [155]. This result is all the more remarkable in that the spectroscopic and thermodynamic properties of the two redox centers appear weakly affected by the cross-linking process, and suggests that an essential segment of the electron transfer path has been lost in the covalent complex. Another system in which such conformational effects could be studied is the physiological complex between tetraheme cytochrome and ferredoxin I from Desulfovibrio desulfuricans Norway the spectral and redox properties of the hemes and of the iron-sulfur cluster are found essentially identical in the covalent and noncovalent complexes and an intracomplex transfer, whose rate has not yet been measured, takes place in the covalent species [156]. 

Myers JM, Myers CR (2000) Role of the tetraheme cytochrome CymA in anaerobic electron transport in cells of Shewanella putrefaciens MR-1 with normal levels of menaquinone. Am Soc Microbio J Bact 183 67-75... 

Reaction centers of purple bacteria. The exact composition varies, but the properties of reaction centers from several genera of purple bacteria are similar. In Rhodopseudomonas viridis there are three peptide chains designated H, M, and L (for heavy, medium and light) with molecular masses of 33,28, and 24 kDa, respectively. Together with a 38-kDa tetraheme cytochrome (which is absent from isolated reaction centers of other species) they form a 1 1 1 1 complex. This constitutes reaction center P870. The three-dimensional structure of this entire complex has been determined to 0.23-nm resolution288 319 323 (Fig. 23-31). In addition to the 1182 amino acid residues there are four molecules of bacteriochlorophyll (BChl), two of bacteriopheophytin (BPh), a molecule of menaquinone-9, an atom of nonheme iron, and four molecules of heme in the c type cytochrome. In 1984, when the structure was determined by Deisenhofer and Michel, this was the largest and most complex object whose atomic structure had been described. It was also one of the first known structures for a membrane protein. The accomplishment spurred an enormous rush of new photosynthesis research, only a tiny fraction of which can be mentioned here. 

The quinone QA (the secondary acceptor) is next reduced by the BPh radical in 200 ps with development of a characteristic EPR signal321 330 at g = 1.82. Over a much longer period of time ( 320 ns) an electron passes from the tetraheme cytochrome subunit to the Chl+ radical in the special pair.323/323a y ie relatively slow rate of this reaction may be related to the fact that the bacteriochlorophyll of the special pair is 2.1 nm (center-to-center) from the nearest heme in the... 

Cyclic photophosphorylation in purple bacteria. QH2 is eventually dehydrogenated in the cytochrome bc1 complex, and the electrons can be returned to the reaction center by the small soluble cytochrome c2, where it reduces the bound tetraheme cytochrome or reacts directly with the special pair in Rhodobacter spheroides. The overall reaction provides for a cyclic photophosphorylation (Fig. 23-32) that pumps 3-4 H+ across the membrane into the periplasmic space utilizing the energy of the two photoexcited electrons. 

Dohse, B., Mathis, P., Wachtveitl, J., Laussermair, E., Iwata, S., Michel, H., and Oesterhelt, D., 1995, Electron-transfer from the tetraheme cytochrome to the special pair In the Rhodopseudomonas viridis reaction-centeroeffect of mutations of tyrosine L162 Biochemistry 34 11335nll343. 

Ortega, J. M., Drepper, F., and Mathis, P., 1999, Electron transfer between cytochrome c2 and the tetraheme cytochrome c in Rhodopseudomonas viridis Photosyn. Res. 59 1479 157. 

Osyczka, A., Nagashima, K. V. P., Sogabe, S., Miki, K., Yoshida, M., Shimada, K., and Matsuura, K., 1998, Interaction site for soluble cytochromes on the tetraheme cytochrome subunit bound to the bacterial photosynthetic reaction center mapped by site-directed mutagenesis Biochemistry 37 11732911744. 

C554 is proposed to bind, and may thus be the electron exit heme. Cytochrome C554 also has two coplanar diheme pairs, which may indicate that it can also accept two electrons simultaneously. This cytochrome then transfers electrons to the membrane-bound tetraheme cytochrome Cm552 (see Section 4), which is a good candidate to reduce the membrane ubiquinone pool, from where electrons are partitioned between the ammonia monooxygenase reaction, the aerobic respiratory chain, and reverse electron transport. ... 

Flavocytochrome c Fumarate Reductase and Shewanella Small Tetraheme Cytochrome... 

In contrast to bacteria that do not contain the RC-associated cytochrome, the polypeptide chain of the M-subunit of bacteria of the second kind has been found to have 20 more residues at the C-terminus. It has been suggested that the extra twenty-odd amino-acid residues are used to hold, or snatch the (tetrajheme subunits. Bacteria such as Rb. sphaeroides, which lack this 20-residue extension into the periplasmic space, may not be able to snatch a tetraheme cytochrome subunit if it were available. 

We now discuss kinetic evidence that supports the notion that a reduced cytochrome is the direct electron donor to the photooxidized P870. . In subsequent sections we discuss properties and reactions of the RC-associated cytochromes, i.e., those cytochromes that are firmly associated with the reaction centers. The topics to be discussed include the temperature-insensitive electron transfer from the cytochrome to the reaction center and the spatial arrangement of the hemes in the tetraheme cytochrome subunit. 

Fig. 9. (A) EPR spectra of Rp. viridis chromatophores poised at +473 mV (a), +180 mV (b) and -158 mV (c). Two prominent lines at g=3.3 and 3.09 are indicated. The broad band near 260 mT is due to ferricyanide used as a redox mediator. (B) redox titration of the g=3.3 and g=3.09 EPR signals. The dashed line in the low-potential wave of the fip3.3 titration is a one-component fit yielding a midpoint potential of -20 mV. The inset (B, c) shows the shift in field position of the g=3.3 line plotted as a function of redox potential. Data points for titrations in the positive and negative directions are represented by solid and open symbols, respectively. Figure source Nitschke and Rutherford (1989) Tetraheme cytochrome c subunit of Rhodopseudomonas viridis characterized by EPR. Biochemistry 28 3162.

Table 1. Summary of experimental data obtained by EPR spectroscopy on g, kinetics of photooxidation of the four cytochromes in Rp. viridis. Data from Nitschke and Rutherfored (1989) Tetraheme cytochrome c subunit of Rhodopseudomonas viridis bv EPR. Biochemistry 28 3161-3168.

JM Ortega and P Mathis (1992) Effect of temperature of eiectron transfer from the tetraheme cytochrome to the primary donor in Rhodopseudomonas viridis. FEBS Lett 301 45-48... 

W Nitschke M Jubault-Bregler and AW Rutherford (1993) The reaction center associated tetraheme cytochrome subunit from Chromatium vinosum revisited a reexamination of its EPR properties. Biochemistry 32 8871-8879... 

Upadhyay AK, Hooper AB, Hendrich MP (2006) NO reductase activity of the tetraheme cytochrome c-554 of Nitrosomonas europaea. J Am Chem Soc 128 4330-4337 Valkova-Valchanova MB, Chan SHP (1994) Purification and characterization of two new c-type cytochromes involved in Fe2+ oxidation from Thiobacillus ferrooxidans. FEBS Lett 288 159-162... 

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