Structure

The overall structure contains 19 transmembrane helices that are arranged in a nearly oval shape. The protein contains two structurally similar subunits each containing nine helices (blue and red) and one smaller subunit, CydX, with one transmembrane helix. The subunits are interacting using hydrophobic residues and symmetry at the interfaces. The CydX subunit, whose function is not currently known, is positioned in the same way as CydS, which is found in E. coli bd oxidase. Due to its similar structure and position, it has been hypothesized to potentially stabilize heme b558 during potential structural rearrangements of the Q loop upon binding and oxidation of quinol. The Q loop is shown in lime green, and is a hydrophilic region above Cyd A. The lack of hydrogen bonding in this hydrophobic protein allows the protein to be flexible and go through a large conformational change for reduction of dioxygen.

Figure 1. bd oxidase; two structurally similar transmembrane helices in blue and red; CydX subunit in teal; Q loop in lime green.

Disease

Relevance

Structural highlights

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