2BQ4

Crystal structure of type I cytochrome c3 from Desulfovibrio africanus

Summary for 2BQ4

• Entry DOI: 10.2210/pdb2bq4/pdb
• Related: 1A2I 1E39 1GM4 1GMB 1GX7 1GYO 1I77 1IT1 1J0O 1J0P 1JRX 1JRY 1JRZ 1KSS 1KSU 1LJ1 1M1P 1M64 1MDV 1P2E 1P2H 1Q9I 1QJD 1QN0 1QN1 1QO8 1UP9 1UPD 1W7O 1WAD 1WR5 2BPN 2CTH 3CAO 3CAR 3CYR
• Descriptor: BASIC CYTOCHROME C3, HEME C, CALCIUM ION, ... (4 entities in total)
• Functional Keywords: basic cytochrome c3, electron transfer, sulfate reducing bacteria, sad, heme, iron, electron transport
• Biological source: DESULFOVIBRIO AFRICANUS
• Cellular location: Periplasm: P94691
• Total number of polymer chains: 2
• Total formula weight: 30156.87

Authors

Czjzek, M.,Pieulle, L.,Morelli, X.,Guerlesquin, F.,Hatchikian, E.C. (deposition date: 2005-04-27, release date: 2005-05-19, Last modification date: 2024-10-23)

Primary citation

Pieulle, L.,Morelli, X.,Gallice, P.,Lojou, E.,Barbier, P.,Czjzek, M.,Bianco, P.,Guerlesquin, F.,Hatchikian, E.C.
The Type I / Type II Cytochrome C(3) Complex: An Electron Transfer Link in the Hydrogen-Sulfate Reduction Pathway.
J.Mol.Biol., 354:73-, 2005

PubMed Abstract: In Desulfovibrio metabolism, periplasmic hydrogen oxidation is coupled to cytoplasmic sulfate reduction via transmembrane electron transfer complexes. Type II tetraheme cytochrome c3 (TpII-c3), nine-heme cytochrome c (9HcA) and 16-heme cytochrome c (HmcA) are periplasmic proteins associated to these membrane-bound redox complexes and exhibit analogous physiological function. Type I tetraheme cytochrome c3 (TpI-c3) is thought to act as a mediator for electron transfer from hydrogenase to these multihemic cytochromes. In the present work we have investigated Desulfovibrio africanus (Da) and Desulfovibrio vulgaris Hildenborough (DvH) TpI-c3/TpII-c3 complexes. Comparative kinetic experiments of Da TpI-c3 and TpII-c3 using electrochemistry confirm that TpI-c3 is much more efficient than TpII-c3 as an electron acceptor from hydrogenase (second order rate constant k = 9 x 10(8) M(-1) s(-1), K(m) = 0.5 microM as compared to k = 1.7 x 10(7) M(-1) s(-1), K(m) = 40 microM, for TpI-c3 and TpII-c3, respectively). The Da TpI-c3/TpII-c3 complex was characterized at low ionic strength by gel filtration, analytical ultracentrifugation and cross-linking experiments. The thermodynamic parameters were determined by isothermal calorimetry titrations. The formation of the complex is mainly driven by a positive entropy change (deltaS = 137(+/-7) J mol(-1) K(-1) and deltaH = 5.1(+/-1.3) kJ mol(-1)) and the value for the association constant is found to be (2.2(+/-0.5)) x 10(6) M(-1) at pH 5.5. Our thermodynamic results reveal that the net increase in enthalpy and entropy is dominantly produced by proton release in combination with water molecule exclusion. Electrostatic forces play an important role in stabilizing the complex between the two proteins, since no complex formation is detected at high ionic strength. The crystal structure of Da TpI-c3 has been solved at 1.5 angstroms resolution and structural models of the complex have been obtained by NMR and docking experiments. Similar experiments have been carried out on the DvH TpI-c3/TpII-c3 complex. In both complexes, heme IV of TpI-c3 faces heme I of TpII-c3 involving basic residues of TpI-c3 and acidic residues of TpII-c3. A secondary interacting site has been observed in the two complexes, involving heme II of Da TpII-c3 and heme III of DvH TpI-c3 giving rise to a TpI-c3/TpII-c3 molar ratio of 2:1 and 1:2 for Da and DvH complexes, respectively. The physiological significance of these alternative sites in multiheme cytochromes c is discussed.

PubMed: 16226767
DOI: 10.1016/J.JMB.2005.09.036

Experimental method

X-RAY DIFFRACTION (1.68 Å)