The menD and menE homologs code for 2-succinyl-6-hydroxyl-2,4-cyclohexadiene-1-carboxylate synthase and O-succinylbenzoic acid–CoA synthase in the phylloquinone biosynthetic pathway of Synechocystis sp. PCC 6803

• Published in: Biochimica et biophysica acta Vol. 1557; no. 1-3; pp. 67 - 76
• Main Authors: Wade Johnson, T, Naithani, Sushma, Stewart, Charles, Zybailov, Boris, Daniel Jones, A, Golbeck, John H, Chitnis, Parag R
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 06-03-2003
• Subjects: Chromatography, High Pressure Liquid; Cyanobacteria - enzymology; Cyanobacteria - genetics; Cyanobacteria - growth & development; Electron Spin Resonance Spectroscopy; Electron Transport; Gene Silencing; Genes, Bacterial; menD; menE; Oxo-Acid-Lyases - genetics; Oxo-Acid-Lyases - metabolism; Photosynthetic Reaction Center Complex Proteins - analysis; Photosystem I; Phylloquinone; Plastoquinone; Restriction Mapping; Spectrometry, Fluorescence - methods; Succinate-CoA Ligases - genetics; Succinate-CoA Ligases - metabolism; Synechocystis; Vitamin K 1 - metabolism; Photosystem I; Phylloquinone; Synechocystis; Plastoquinone; menE; menD
• ISSN: 0005-2728; 0006-3002; 1879-2650
• DOI: 10.1016/S0005-2728(02)00396-1

The genome of the cyanobacterium
Synechocystis sp. PCC 6803 contains genes identified as
menD and
menE, homologs of
Escherichia coli genes that code for 2-succinyl-6-hydroxyl-2,4-cyclohexadiene-1-carboxylate (SHCHC) synthase and
O-succinylbenzoic acid–CoA ligase in the menaquinone biosynthetic pathway. In cyanobacteria, the product of this pathway is 2-methyl-3-phytyl-1,4-naphthoquinone (phylloquinone), a molecule used exclusively as an electron transfer cofactor in Photosystem (PS) I. The
menD
− and
menE
− strains were generated, and both were found to lack phylloquinone. Hence, no alternative pathways exist in cyanobacteria to produce
O-succinylbenzoyl–CoA. Q-band EPR studies of photoaccumulated quinone anion radical and optical kinetic studies of the P700
+ [F
A/F
B]
− backreaction indicate that in the mutant strains, plastoquinone-9 functions as the electron transfer cofactor in the A
1 site of PS I. At a light intensity of 40 μE m
−2 s
−1, the
menD
− and
menE
− mutant strains grew photoautotrophically and photoheterotrophically, but with doubling times slower than the wild type. Both of which are sensitive to high light intensities. Low-temperature fluorescence studies show that in the
menD
− and
menE
− mutants, the ratio of PS I to PS II is reduced relative to the wild type. Whole-chain electron transfer rates in the
menD
− and
menE
− mutant cells are correspondingly higher on a chlorophyll basis. The slower growth rate and high-light sensitivity of the
menD
− and
menE
− mutants are therefore attributed to a lower content of PS I per cell.