1ls9
Structure of the Cytochrome c6 from the Green Alga Cladophora glomerataStructure of the Cytochrome c6 from the Green Alga Cladophora glomerata
Structural highlights
FunctionEvolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThis is a thorough biochemical, spectroscopic, electrochemical, and structural study of a cytochrome c(6) isolated from the filamentous green alga Cladophora glomerata. The protein sequence, elucidated using chemical and mass spectrometric techniques, features 91 amino acids and the characteristic CXXCH heme-binding motif found in c-type cytochromes. The protein is monomeric in both oxidation forms, thereby putting in question a functional role for protein dimerization. Direct electrochemical measurements established, for the first time, the kinetic and thermodynamic data for the redox process in a cytochrome c(6). In particular, the quasi-reversible and diffusion-controlled redox process is accompanied by negative enthalpy and entropy changes, resulting in an E degrees ' value of 0.352 V at 298 K. The pH-dependent properties of the oxidized protein, detected by UV-visible, NMR, and direct cyclic voltammetry, indicate the presence of two acid-base equilibria occurring in the acidic (pK(a) = 4.5) and alkaline regions (pK(a) = 9.0). NMR and electronic spectra allowed the assignment of these equilibria to deprotonation of heme propionate-7 and to replacement of the axial methionine with another ligand, respectively. The 1.3 A resolution X-ray structure of the oxidized protein, revealing a fold typical for class I cytochromes, suggests that the conserved Lys60 replaces the axial methionine at pH >9. The heme solvent accessibility is low, and no water molecules were found in the vicinity of the axial ligands of the heme Fe. A structure-based alignment of cytochromes c(6), and the direct comparison of their structures, indicate a substantial degree of identity between the tertiary structures and suggest patches involved in protein-protein interaction. In particular, the surface electrostatic potential of cytochromes c(6) features a hydrophobic region around the heme cofactor, and a backside surface rich in negative charges. Structural basis for the molecular properties of cytochrome c6.,Dikiy A, Carpentier W, Vandenberghe I, Borsari M, Safarov N, Dikaya E, Van Beeumen J, Ciurli S Biochemistry. 2002 Dec 17;41(50):14689-99. PMID:12475218[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References |
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