title: Regulation of intracellular free calcium concentration during heterocyst differentiation by HetR and NtcA in Anabaena sp. PCC 7120.
abstract: Calcium ions are important to some prokaryotic cellular processes, such as heterocyst differentiation of cyanobacteria. Intracellular free Ca(2+)concentration, [Ca(2+)](i), increases several fold in heterocysts and is regulated by CcbP, a Ca(2+)-binding protein found in heterocyst-forming cyanobacteria. We demonstrate here that CcbP is degraded by HetR, a serine-type protease that controls heterocyst differentiation. The degradation depends on Ca(2+) and appears to be specific because HetR did not digest other tested proteins. CcbP was found to bind two Ca(2+) per molecule with K(D) values of 200 nM and 12.8 microM. Degradation of CcbP releases bound Ca(2+) that contributes significantly to the increase of [Ca(2+)](i) during the process of heterocyst differentiation in Anabaena sp. strain PCC 7120. We suggest that degradation of CcbP is a mechanism of positive autoregulation of HetR. The down-regulation of ccbP in differentiating cells and mature heterocysts, which also is critical to the regulation of [Ca(2+)](i), depends on NtcA. Coexpression of ntcA and a ccbP promoter-controlled gfp in Escherichia coli diminished production of GFP, and the decrease is enhanced by alpha-ketoglutarate. It was also found that NtcA could bind a fragment of the ccbP promoter containing an NtcA-binding sequence in a alpha-ketoglutarate-dependent fashion. Therefore, [Ca(2+)](i) is regulated by a collaboration of HetR and NtcA in heterocyst differentiation in Anabaena sp. strain PCC 7120.
authors.affiliation: State Key Lab of Protein and Plant Genetic Engineering, College of Life Sciences, Peking University, Beijing 100871, China.
authors.forename: Yunming
authors.initials: Y
authors.lastname: Shi
authors.forename: Weixing
authors.initials: W
authors.lastname: Zhao
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Zi
authors.initials: Z
authors.lastname: Ye
authors.forename: Jindong
authors.initials: J
authors.lastname: Zhao
mesh_terms: D017033:Anabaena / Q000378:metabolism*; D001426:Bacterial Proteins / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D004247:DNA / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000502:physiology*; D015536:Down-Regulation; D004926:Escherichia coli / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007700:Kinetics; D011485:Protein Binding; D012697:Serine Endopeptidases / Q000737:chemistry; D013997:Time Factors; D014157:Transcription Factors / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D014157:Transcription Factors; C067403:HetR protein, Bacteria; D049452:Green Fluorescent Proteins; C075617:ntcA protein, Synechococcus; D004247:DNA; D012697:Serine Endopeptidases; D002118:Calcium