1ls9: Difference between revisions

[[Image:1ls9.gif|left|200px]]<br /><applet load="1ls9" size="350" color="white" frame="true" align="right" spinBox="true"  

This 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 &gt;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.

1LS9 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Cladophora_glomerata Cladophora glomerata] with <scene name='pdbligand=HEM:'>HEM</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1LS9 OCA].  

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