Sandbox Reserved 1625: Difference between revisions
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==Introduction== | ==Introduction== | ||
<StructureSection load='6rx4' size='350' frame='true' side='right' caption='E. coli cytochrome bd-1 oxidase. Blue= CydA; green= CydB; yellow= CydX; pink= CydS; gray = hemes and UQ-8.' scene='83/832931/Full/3'>test</scene’> | <StructureSection load='6rx4' size='350' frame='true' side='right' caption='E. coli cytochrome bd-1 oxidase. Blue= CydA; green= CydB; yellow= CydX; pink= CydS; gray = hemes and UQ-8.' scene='83/832931/Full/3'>test</scene’> | ||
=Structure= | |||
=== Subunits === | |||
[https://en.wikipedia.org/wiki/Escherichia_coli ''E. coli''] bd oxidase is made up of four individual subunits.<ref name="Alexander">PMID:31723136</ref> The two major subunits, CydA and CydB, are each composed of one peripheral helix and two bundles of four transmembrane helices. The <scene name='83/832924/Cyda_subunit/6'>CydA subunit</scene> plays the most important role in the oxygen reduction reaction as it contains the Q-loop as well as all three heme groups. The <scene name='83/832924/Cydb_subunit/2'>CydB subunit</scene> harbors the <scene name='83/832924/Ubiquinone/3'>ubiquinone</scene> molecule which provides structural support to the subunit that mimics the three hemes found in CydA.<ref name="Safarian">PMID: 31604309</ref><ref name="Safarian2">PMID: 27126043</ref> The remaining two subunits, CydS and CydX, are both single helix structures that assist in the oxygen reduction reaction. Unique to ''E. coli'', the <scene name='83/832924/Cyds_subunit/4'>CydS subunit</scene> binds to CydA to block oxygen from directly binding to heme b595. The <scene name='83/832924/Cydx_subunit/4'>CydX subunit</scene> promotes the assembly and stability of the oxidase complex. CydX is composed of 37 mostly hydrophilic amino acid residues, including <scene name='83/832924/Glu25/2'>Glu25</scene> that is exposed to the cytoplasm and prevents the helix from fully entering the membrane. <ref name="Alexander">PMID:31723136</ref> | |||
===Q-Loop=== | |||
Another significant structural feature of bd oxidase is the <scene name='83/832924/Q_loop/3'>Q-loop</scene> which is located between TM helices 6 and 7 of the CydA subunit.<ref name="Alexander">PMID:31723136</ref> The periplasmic Q-loop in ''E. coli'' stretches over a length of 136 amino acid residues, making it much longer than the Q-loop in ''Geobacillus thermodentrificans''.<ref name="Safarian">PMID: 27126043</ref> The Q-loop is likely involved in [https://en.wikipedia.org/wiki/Quinone quinone] binding and oxidation. The N-terminal end of this Q-loop is very flexible and likely functions as the hinge that allows for quinone binding while the C-terminal end is much more rigid which provides stabilization for the enzyme.<ref name="Alexander">PMID:31723136</ref> | |||
== Function == | == Function == | ||
The <scene name='83/832931/Full/4'>cytochrome ''bd'' oxidase</scene> allows bacteria to be resistant to hypoxia, cyanide, nitric oxide, and H<sub>2</sub>O<sub>2</sub><ref name="Harikishore">PMID: 31939065</ref> | The <scene name='83/832931/Full/4'>cytochrome ''bd'' oxidase</scene> allows bacteria to be resistant to hypoxia, cyanide, nitric oxide, and H<sub>2</sub>O<sub>2</sub><ref name="Harikishore">PMID: 31939065</ref> | ||
== Disease == | == Disease == | ||
