Proton-assisted Two-electron Transfer in Natural Variants of Tetraheme Cytochromes from Desulfomicrobium Sp.

Abstract

The tetraheme cytochrome c 3 isolated from Desulfomicrobium baculatum (DSM 1743) (Dsmb) was cloned, and the sequence analysis showed that this cytochrome differs in just three amino acid residues from the cytochrome c 3 isolated from Desulfomicrobium norvegicum (Dsmn): (DsmnXXDsmb) Thr-37 3 Ser, Val-45 3 Ala, and Phe-88 3 Tyr. X-ray crystallography was used to determine the structure of cytochrome c 3 from Dsmb, showing that it is very similar to the published structure of cytochrome c 3 from Dsmn. A detailed thermodynamic and kinetic characterization of these two tetraheme cytochromes c 3 was performed by using NMR and visible spectroscopy. The results obtained show that the network of cooperativities between the redox and protonic centers is consistent with a synergetic process to stimulate the hydrogen uptake activity of hydrogenase. This is achieved by increasing the affinity of the cytochrome for protons through binding electrons and, reciprocally, by favoring a concerted two-electron transfer assisted by the binding of proton(s). The data were analyzed within the framework of the differences in the primary and tertiary structures of the two proteins, showing that residue 88, close to heme I, is the main cause for the differences in the microscopic thermodynamic parameters obtained for these two cytochromes c 3 . This comparison reveals how replacement of a single amino acid can tune the functional properties of energy-transducing proteins, so that they can be optimized to suit the bioenergetic constraints of specific habitats.

Redox Interaction of Cytochromec3with [NiFe] Hydrogenase fromDesulfovibrio vulgarisMiyazaki F

“…The iron-iron distance between two redox centers (14.4 and 13.6 Å for models nos. 1 and 2) is greater than those in the model structure for the cyt c 3 On the other hand, evaluation for the conservation of intermolecular salt bridges and hydrogen bonds is not straightforward because of the low homology in cyt c 3 amino acid sequence. DVMF cyt c 3 is classified to the 2-4-2-4 group on the basis of heme attachment sites (31).…”

Metalloproteins Containing Cytochrome, Iron–Sulfur, or Copper Redox Centers

“…340,501,502 On the other hand, the pH-dependent reduction potential difference, over a range of 10 pH units, can be ∼200 mV. 503 Such property is crucial for proper charge separation to generate a promotive force that drives ATP synthesis.…”

Homotropic and heterotropic interactions in cytochromes c3 from sulphate reducing bacteria

“…9 calculated at pH 6.15 and solution potential −260 mV using the thermodynamic parameters of the protein from Dsm. norvegicum [2]. A deprotonated molecule in stage 3 with haems I, II, and IV oxidised (labelled 124 in Fig.…”

“…X‐ray structure of the tetrahaem cytochrome c 3 from Dsm. baculatum [2]. The haems are numbered according to the positions of their binding sites in the aminoacid sequence.…”