The post-translational modification in cytochrome c oxidase is required to establish a functional environment of the catalytic site.
Mutation of tyrosine-288 to a phenylalanine in cytochrome c oxidase from Rhodobacter sphaeroides drastically alters its properties. Tyr-288 lies in the CuB-cytochrome a3 binuclear catalytic site and forms a hydrogen bond with the hydroxy group on the farnesyl side chain of the heme. In addition, through a post-translational modification, Y288 is covalently linked to one of the histidine ligands that is coordinated to CuB. In the Y288F mutant enzyme, the "as-isolated" preparation is a mixture of reduced cytochrome a and oxidized cytochrome a3. The cytochrome a3 heme, which is largely six-coordinate low-spin in both oxidation states of the mutant, cannot be reduced by cytochrome c, but only by dithionite, possibly due to a large decrease in its reduction potential. It is postulated that the Y288F mutation prevents the post-translational modification from occurring. As a consequence, the catalytic site becomes disrupted. Thus, one role of the post-translational modification is to stabilize the functional catalytic site by maintaining the correct ligands on CuB, thereby preventing nonfunctional ligands from coordinating to the heme.
Das
T K
TK
Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Pecoraro
C
C
Tomson
F L
FL
Gennis
R B
RB
Rousseau
D L
DL
D001665:Binding Sites / Q000235:genetics; D002384:Catalysis; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D008024:Ligands; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010649:Phenylalanine / Q000235:genetics; D011499:Protein Processing, Post-Translational; D012242:Rhodobacter sphaeroides / Q000201:enzymology / Q000235:genetics; D013059:Spectrum Analysis, Raman; D014443:Tyrosine / Q000235:genetics
D008024:Ligands; D014443:Tyrosine; D006418:Heme; D010649:Phenylalanine; D003576:Electron Transport Complex IV