Protein Family Models

Cytochrome c oxidase (E.C:7.1.1.9) is a key enzyme in aerobic metabolism. Proton pumping haem-copper oxidases represent the terminal, energy-transfer enzymes of respiratory chains in prokaryotes and eukaryotes. The CuB-haem a3 (or haem o) binuclear centre, associated with the largest subunit I of cytochrome c and ubiquinol oxidases (E.C:1.10.3.11), is directly involved in the coupling between dioxygen reduction and proton pumping [1,2,3,4]. Some terminal oxidases generate a transmembrane proton gradient across the plasma membrane (prokaryotes) or the mitochondrial inner membrane (eukaryotes). The enzyme complex consists of 3-4 subunits (prokaryotes) up to 13 polypeptides (mammals) of which only the catalytic subunit (equivalent to mammalian subunit I (COXI) is found in all haem-copper respiratory oxidases. The presence of a bimetallic centre (formed by a high-spin haem and copper B) as well as a low-spin haem, both ligated to six conserved histidine residues near the outer side of four transmembrane spans within CO I is common to all family members [2,3]. [1]. 8638158. The whole structure of the 13-subunit oxidized cytochrome c oxidase at 2.8 A. Tsukihara T, Aoyama H, Yamashita E, Tomizaki T, Yamaguchi H, Shinzawa-Itoh K, Nakashima R, Yaono R, Yoshikawa S;. Science 1996;272:1136-1144. [2]. 8013452. Evolution of cytochrome oxidase, an enzyme older than atmospheric oxygen. Castresana J, Lubben M, Saraste M, Higgins DG;. EMBO J. 1994;13:2516-2525. [3]. 31489376. Dimeric structures of quinol-dependent nitric oxide reductases (qNORs) revealed by cryo-electron microscopy. Gopalasingam CC, Johnson RM, Chiduza GN, Tosha T, Yamamot. TRUNCATED at 1650 bytes (from Pfam)

Date:

2024-10-16

This family (QoxB) encodes subunit I of the aa3-type quinone oxidase, one of several bacterial terminal oxidases [1]. This complex couples oxidation of reduced quinones with the reduction of molecular oxygen to water and the pumping of protons to form a proton gradient utilized for ATP production. aa3-type oxidases contain two heme a cofactors as well as copper atoms in the active site.

Gene:

qoxB

Date:

2024-05-30

This large family represents subunit I's (CtaD, CoxA, CaaA) of cytochrome c oxidases of bacterial origin. Cytochrome c oxidase is the component of the respiratory chain that catalyzes the reduction of oxygen to water. Subunits I-III form the functional core of the enzyme complex. Subunit I is the catalytic subunit of the enzyme. Electrons originating in cytochrome c are transferred via the copper A center of subunit II and heme a of subunit I to the bimetallic center formed by heme a3 and copper B. This cytochrome c oxidase shows proton pump activity across the membrane in addition to the electron transfer. In the bacilli an apparent split (paralogism) has created a sister clade (TIGR02882) encoding subunits (QoxA) of the aa3-type quinone oxidase complex which reacts directly with quinones, bypassing the interaction with soluble cytochrome c. This model attempts to exclude these sequences, placing them between the trusted and noise cutoffs. These families, as well as archaeal and eukaryotic cytochrome c subunit I's are included within the superfamily model, PF00115.

Gene:

ctaD

Date:

2024-05-30