Journal Article

Functional Differentiation of Two Analogous Coproporphyrinogen III Oxidases for Heme and Chlorophyll Biosynthesis Pathways in the Cyanobacterium <i>Synechocystis</i> sp. PCC 6803

Takeaki Goto, Rina Aoki, Kei Minamizaki and Yuichi Fujita

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 51, issue 4, pages 650-663
Published in print April 2010 | ISSN: 0032-0781
Published online April 2010 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcq023
Functional Differentiation of Two Analogous Coproporphyrinogen III Oxidases for Heme and Chlorophyll Biosynthesis Pathways in the Cyanobacterium Synechocystis sp. PCC 6803

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Coproporphyrinogen III oxidase (CPO) catalyzes the oxidative decarboxylation of coproporphyrinogen III to form protoporphyrinogen IX in heme biosynthesis and is shared in chlorophyll biosynthesis in photosynthetic organisms. There are two analogous CPOs, oxygen-dependent (HemF) and oxygen-independent (HemN) CPOs, in various organisms. Little information on cyanobacterial CPOs has been available to date. In the genome of the cyanobacterium Synechocystis sp. PCC 6803 there is one hemF-like gene, sll1185, and two hemN-like genes, sll1876 and sll1917. The three genes were overexpressed in Escherichia coli and purified to homogeneity. Sll1185 showed CPO activity under both aerobic and anaerobic conditions. While Sll1876 and Sll1917 showed absorbance spectra indicative of Fe–S proteins, only Sll1876 showed CPO activity under anaerobic conditions. Three mutants lacking one of these genes were isolated. The Δsll1185 mutant failed to grow under aerobic conditions, with accumulation of coproporphyrin III. This growth defect was restored by cultivation under micro-oxic conditions. The growth of the Δsll1876 mutant was significantly slower than that of the wild type under micro-oxic conditions, while it grew normally under aerobic conditions. Coproporphyrin III was accumulated at a low but significant level in the Δsll1876 mutant grown under micro-oxic conditions. There was no detectable phenotype in Δsll1917 under the conditions we examined. These results suggested that sll1185 encodes HemF as the sole CPO under aerobic conditions and that sll1876 encodes HemN operating under micro-oxic conditions, together with HemF. Such a differential operation of CPOs would ensure the stable supply of tetrapyrrole pigments under environments where oxygen levels fluctuate greatly.

Keywords: Chlorophyll; Coproporphyrinogen III oxidase; Cyanobacteria; hemF; hemN; Synechocystis sp. PCC 6803

Journal Article.  8252 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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