CydX is a subunit of Escherichia coli cytochrome bd terminal oxidase and essential for assembly and stability of the di-heme active site

Abstract

cydB , cydA , and cydX physically interacts by affinity technology (1, 2)

Cytochrome bd from Escherichia coli catalyzes peroxynitrite decomposition

“…This confirms that in the isolated enzyme all the three hemes, including the di-heme active site components, heme b 595 and heme d, were present as expected for a bd-type oxidase [14]. Based on recent reports [23][24][25], this suggests that the purified enzyme likely included the newly discovered small subunit CydX. The enzyme concentration was determined from the dithionitereduced-minus-'as prepared' difference absorption spectrum using Δε 628-607 = 10.8 mM −1 cm −1 [30].…”

“…Cytochrome bd is composed of two major membrane-spanning polypeptides, subunits I (CydA, 57 kDa) and II (CydB, 43 kDa), and a small protein, named CydX (4 kDa). The latter has been recently shown to be essential for enzymatic activity and proposed to be an additional subunit of the complex, needed for either the assembly or the stability of the enzyme [23][24][25]. Cytochrome bd bears two b-type hemes, the low-spin b 558 and the high-spin b 595 , and one chlorin, heme d. Heme b 558 accepts electrons from the quinol substrate, whereas heme d is the site where the oxygen chemistry takes place.…”

The long Q‐loop of Escherichia coli cytochrome bd oxidase is required for assembly and structural integrity

“…Three expression plasmids were generated from plasmid pET28b(+) cydA his BX that encodes the E. coli bd ‐I oxidase . The newly designed plasmids were designated as Q short , Q helix , and Q Geo .…”

“…It was found that bd oxidases contain a third subunit, called CydX in Escherichia coli and CydS in Geobacillus thermodenitrificans . CydX consists of 30–40 amino acids, and it is encoded by the cyd operon.…”

The CydDC Family of Transporters and Their Roles in Oxidase Assembly and Homeostasis

“…lacking CydX exhibit diminished oxidase activity which can be restored by the addition of cydX on a plasmid (Van Orsdel et al, 2013) and silver staining shows that CydX is present in stoichiometric amounts with CydA and CydB (Hoeser, Hong, Gehmann, Gennis, & Friedrich, 2014), confirming CydX as a third subunit of cytochrome bd-I. CydX is required for either the insertion or the stability of haem d and b 595 thought to make up the di-haem active site of cytochrome bd-I; UV-visible difference spectroscopy revealed that the signals of haem d and b 595 are lost when CydA and CydB are not accompanied by CydX.…”