ChlR protein of Synechococcus sp. PCC 7002 is a transcription activator that uses an oxygen-sensitive [4Fe-4S] cluster to control genes involved in pigment biosynthesis.
Synechococcus sp. PCC 7002 and many other cyanobacteria have two genes that encode key enzymes involved in chlorophyll a, biliverdin, and heme biosynthesis: acsFI/acsFII, ho1/ho2, and hemF/hemN. Under atmospheric O2 levels, AcsFI synthesizes 3,8-divinyl protochlorophyllide from Mg-protoporphyrin IX monomethyl ester, Ho1 oxidatively cleaves heme to form biliverdin, and HemF oxidizes coproporphyrinogen III to protoporphyrinogen IX. Under microoxic conditions, another set of genes directs the synthesis of alternative enzymes AcsFII, Ho2, and HemN. In Synechococcus sp. PCC 7002, open reading frame SynPCC7002_A1993 encodes a MarR family transcriptional regulator, which is located immediately upstream from the operon comprising acsFII, ho2, hemN, and desF (the latter encodes a putative fatty acid desaturase). Deletion and complementation analyses showed that this gene, denoted chlR, is a transcriptional activator that is essential for transcription of the acsFII-ho2-hemN-desF operon under microoxic conditions. Global transcriptome analyses showed that ChlR controls the expression of only these four genes. Co-expression of chlR with a yfp reporter gene under the control of the acsFII promoter from Synechocystis sp. PCC 6803 in Escherichia coli demonstrated that no other cyanobacterium-specific components are required for proper functioning of this regulatory circuit. A combination of analytical methods and Mössbauer and EPR spectroscopies showed that reconstituted, recombinant ChlR forms homodimers that harbor one oxygen-sensitive [4Fe-4S] cluster. We conclude that ChlR is a transcriptional activator that uses a [4Fe-4S] cluster to sense O2 levels and thereby control the expression of the acsFII-ho2-hemN-desF operon.
From the Departments of Biochemistry and Molecular Biology and.
Marcus
M
Ludwig
Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802 and.
Maria-Eirini
ME
Pandelia
From the Departments of Biochemistry and Molecular Biology and.
Chyue Yie
CY
Chew
Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802 and.
Bo
B
Zhang
From the Departments of Biochemistry and Molecular Biology and Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802 and.
John H
JH
Golbeck
From the Departments of Biochemistry and Molecular Biology and Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802 and.
Carsten
C
Krebs
From the Departments of Biochemistry and Molecular Biology and the Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717 dab14@psu.edu.
Donald A
DA
Bryant
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism; D009876:Operon; D046940:Synechococcus / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; D014157:Transcription Factors
Cyanobacteria; Gene Expression; Iron-Sulfur Protein; Transcription Regulation; Transcriptomics