Structure of cytochrome c oxidase in deoxycholate-drived two-dimensional crystals.

The structure of the two-dimensional crystals of cytochrome oxidase prepared with deoxycholate has been investigated. The crystals have space group p12₁ and contain a monomer (two heme-two copper complex) in the asymmetric unit. They are in the form of sheets and contain no continuous bilayer; the entire surface of the molecule seems to be visible in negatively stained samples. The monomer is roughly 110 Å long and resembles a lopsided “Y”. The domains which form the arms of the Y are 55 Å in length and have a center to center separation of 40 Å. These domains are on the matrix side of the molecule and are thought to be buried in the bilayer of the inner mitochondrial membrane. The cytoplasmic side of the molecule is composed of the single large domain which is the stem of the Y. The overall structure matches that of cytochrome oxidase seen in the p22₁2₁ crystals derived by Triton X100 treatment of mitochondria.