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Introduction

bd Oxidase is a type of quinol-dependent terminal oxidase found exclusively in prokaryotes. With a very high oxygen affinity, bd oxidases play a vital role in the oxidative phosphorylation pathway in both gram-positive and gram-negative bacteria. bd oxidases responsibility in the oxidative phosphorylation pathway allows the protein to also assist as a key survival factor in the bacterial stress response against antibacterial drugs. Given this knowledge, bd oxidases have become an area of scientific research worth pursuing as they could serve as an ideal target for antimicrobial drug development.

Figure 1: Overall schematic representation of cytochrome bd; General display of the reduction of molecular oxygen into water using the quinol as a reducing substrate. [1]

The overall mechanism of bd oxidases involves an exergonic reduction reaction of molecular oxygen into water (Figure 1). During this reaction, a proton gradient is generated in order to assist in the conservation of energy. Unlike other terminal oxidases, bd oxidases do not use a proton pump. Instead, bd oxidases use a form of vectorial chemistry that releases protons from the quinol oxidation into the positive, periplasmic side of the membrane. Protons that are required for the water formation are then consumed from the negative, cytoplasmic side of the membrane, thus creating the previously mentioned proton gradient.

Figure 2: 6RX4 monomer subunit; alpha helices in teal, beta sheets in purple.

This page will be specifically focusing on the structure and overall function of the 6RX4 bd oxidase. 6RX4 is a part of the long(L) quinol-binding domain subfamily that terminal oxidases are classified into. The L-subfamily of bd oxidases are responsible for the survival of acute infectious diseases such as E.Coli and salmonella. The 6RX4's three groups, its periplasmically exposed , and four protein subunits will be of primary focus when identifying the relationship between structure and function.

Function

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Disease

Relevance

Structural highlights