title: CphA2 is a novel type of cyanophycin synthetase in N2-fixing cyanobacteria.
abstract: Most cyanobacteria use a single type of cyanophycin synthetase, CphA1, to synthesize the nitrogen-rich polymer cyanophycin. The genomes of many N2-fixing cyanobacteria contain an additional gene that encodes a second type of cyanophycin synthetase, CphA2. The potential function of this enzyme has been debated due to its reduced size and the lack of one of the two ATP-binding sites that are present in CphA1. Here, we analysed CphA2 from Anabaena variabilis ATCC 29413 and Cyanothece sp. PCC 7425. We found that CphA2 polymerized the dipeptide β-aspartyl-arginine to form cyanophycin. Thus, CphA2 represents a novel type of cyanophycin synthetase. A cphA2 disruption mutant of A. variabilis was generated. Growth of this mutant was impaired under high-light conditions and nitrogen deprivation, suggesting that CphA2 plays an important role in nitrogen metabolism under N2-fixing conditions. Electron micrographs revealed that the mutant had fewer cyanophycin granules, but no alteration in the distribution of granules in its cells was observed. Localization of CphA2 by immunogold electron microscopy demonstrated that the enzyme is attached to cyanophycin granules. Expression of CphA1 and CphA2 was examined in Anabaena WT and cphA mutant cells. Whilst the CphA1 level increased upon nitrogen deprivation, the CphA2 level remained nearly constant.
authors.affiliation: Institut für Biologie, Humboldt-Universität zu Berlin, Chausseestraße 117, 10115 Berlin, Germany.
authors.forename: Friederike
authors.initials: F
authors.lastname: Klemke
authors.affiliation: Institut für Biologie, Humboldt-Universität zu Berlin, Chausseestraße 117, 10115 Berlin, Germany.|Department of Life Sciences, Imperial College London, London SW7 2AZ, UK.
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: Nürnberg
authors.affiliation: Institut für Biologie, Humboldt-Universität zu Berlin, Chausseestraße 117, 10115 Berlin, Germany.
authors.forename: Karl
authors.initials: K
authors.lastname: Ziegler
authors.affiliation: Institut für Biologie, Humboldt-Universität zu Berlin, Chausseestraße 117, 10115 Berlin, Germany.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Beyer
authors.affiliation: Zentrum für Ultrastrukturelle Diagnostik im IIT, Universitätsstraße 25, 33615 Bielefeld, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Kahmann
authors.affiliation: Institut für Biologie, Humboldt-Universität zu Berlin, Chausseestraße 117, 10115 Berlin, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lockau
authors.affiliation: Institut für Biologie, Humboldt-Universität zu Berlin, Chausseestraße 117, 10115 Berlin, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Volkmer
mesh_terms: D046870:Anabaena variabilis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D046889:Cyanothece / Q000201:enzymology* / Q000378:metabolism*; D004151:Dipeptides / Q000378:metabolism; D055786:Gene Knockout Techniques; D008027:Light; D009584:Nitrogen / Q000378:metabolism; D010453:Peptide Synthases / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004151:Dipeptides; C024250:cyanophycin; D010453:Peptide Synthases; C113257:cyanophycin synthase, bacteria; D009584:Nitrogen