Binuclear centre structure of terminal protonmotive oxidases

Abstract

The recent proliferation of data obtained from mutant forms of cytochrome oxidase and analogous enzymes has necessitated a re-examination of existing structural models. A new model is proposed, consistent with these data, which brings several protonatable residues (Y244, D298, D300, T309. T316, K319, T326) into the vicinity of the binuclear centre. suggestive of a proton-transferring function. In addition. we also consider those residues which may participate m electron transport between Cu, and haem a. We suggest several potential lines of investigation.

Insight into topological and functional relationships of cytochrome c oxidase subunit I of Saccharomyces cerevisiae by means of intragenic complementation

“…In contrast to L13, it grows poorly on glycerol indicating a partial cytochrome oxidase activity. This CO recombination effect may indicate, as suggested by Brown et al [7,11], that helix 8 and position 316 are also located in the binuclear centre environment or in the channel leading to it from the negative aqueous phase. Mutant L53 (G352V), carrying a glycine to valine mutation in position 352 located in helix 9 has an optically detectable cytochrome oxidase and shows no modification of the CO recombination kinetics [l 11.…”

“…2). According to Brown et al [7], this face of the helix 8 may be oriented towards Cu, and form part of the proton channel into the binuclear centre.…”

“…Localisation of amino acid substitutions in the mode1 of the cytochrome oxidase subunit I. The figure was based on the models proposed in [7] and [13]. Six of the 12 helices are presented Each helix is indicated as a helical wheel.…”

“…It contains the ligands for haem a and the binuclear centre, haem a&uB. Three-dimensional models for the structure of subunit I have been made on the basis of sequence comparisons, biophysical data and the assignment of the histidine ligands to the metal prosthetic groups [3][4][5][6][7][8]. In a recent model [III, the binuclear centre is located at about the same level as haem a, near the outer positive side of the membrane.…”

“…Mutant L45 with a replacement of aspartate to asparagine (D369N) in position 369 located in the extramembranous loop between helices 9 and 10, has no optically detectable cytochrome oxidase and is totally unable to grow on glycerol. The mutated position is included in a sequence of seven well conserved amino acids which might be involved in intersubunit electron transfer between CuA in subunit II and haem u in subunit I [7]. It is also separated by seven amino acids from histidine-376 which is the ligand of haem a, in the binuclear centre.…”