User talk:Vishnu07/arc ecoli

ARC System in E.Coli
ARC system is the aerobic respiratory control system. Escherichia coli has several elaborate sensing mechanisms for response to the availability of oxygen and the presence of other electron acceptors. The adaptive responses are coordinated by a group of global regulators, which include the one component Fnr protein, and the  two-component Arc system. The two-component signal transduction system, consists of ArcB protein, a transmembrane sensor kinase and ArcA protein, the cognate response regulator.Under anoxic or environmentally reducing conditions, the sensor kinase (ArcB) is stimulated to autophosphorylate at the expense of ATP and subsequently transphosphorylates ArcA, hereby activating it as a transcriptional regulator of a family of  about 30 target operons.

ArcA and ArcB
ArcB is a complex, membrane-bound protein comprising at least three cytoplasmic domains,an N-terminal transmitter domain with a conserved His292 residue (H1), a central receiver domain with a conserved Asp576 residue (D1), and a C-terminal alternative transmitter domain with a conserved His717 residue (H2). ArcA consists of an N-terminal receiver domain (D2) containing the conserved Asp54 and a C-terminal helix-turn-helix (HTH) domain.

1. Reception of a membrane signal(s) triggers autophosphorylation of H1 at His292. 2. The phosphoryl group can migrate to D1 at Asp576 and subsequently to H2 at His717 3. ArcA receives the phosphoryl group from either His292 or His717

Repression and Induction
— Preceding unsigned comment added by Vishnu07 (talk • contribs) 04:10, 23 September 2011 (UTC) The phosporylated ArcA acts as both repressor and inducer of gene transcription under anaerobic conditions. It is responsible for repression of genes for
 * citric acid cycle enzymes
 * glyoxylate cycle enzymes
 * dehydrogenases for aerobic growth
 * fatty acid oxidation enzymes
 * cytochrome o oxidase

anaerobic induction of gene for
 * pyruvate formate lyase

induction in low oxygen of the genes for:
 * cytochrome d oxidase
 * cobalmine synthesis

Cytochrome Oxidases
— Preceding unsigned comment added by Vishnu07 (talk • contribs) 04:11, 23 September 2011 (UTC) The aerobic respiratory system E.coli contains two terminal oxidases, the cytochrome o oxidase complex and the cytochrome d oxidase complex. Both enzymes catalyse the oxidation of ubiquinol-8 and the reduction of oxygen to water. The cytochrome o oxidase complex encoded by thecyoABCDE operon predominates under high oxygen tension. As oxygen becomes limiting, cytochrome o levels decrease and the cytochrome d oxidase complex, encoded by the cydAB operon, becomes the predominant terminal respiratory enzyme. The microaerobic control of cydAB operon expression is co-ordinated by the arcA and fnr gene products.

Eukaryotic Analogues
Two-component signal transduction systems, which consist of a sensor kinase and a response regulator, are highly conserved in nature and mediate adaptations to a variety of environmental changes. Although these systems have been found in some eukaryotes such as plant and yeast species, they are more prevalent in prokaryotes. The fission yeast Schizosaccharomyces pombe contains an RR (MSC4) that regulates a stress-activated MAP kinase cascade. The pathogenic fungus Candida albicans contains at least two HKs involved in osmoregulation (CASLN1) and hyphal development (COS1/CANIK1). Homologs of COS1/CANIK1 have been identified in the filamentous fungi Neurospora crassa (NIK-1) and Aspergillus nidulans (ANNIK1). They have also been found in plants, such as Arabidopsis thaliana (ETR1, ETR2, ERS, and EIN4) and tomato in which they regulate ethylene-mediated fruit ripening.