TY - JOUR
T1 - 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
AU - Johnson, T. Wade
AU - Naithani, Sushma
AU - Stewart, Charles
AU - Zybailov, Boris
AU - Jones, A. Daniel
AU - Golbeck, John H.
AU - Chitnis, Parag R.
N1 - Funding Information:
This work was supported by the National Science Foundation Grants (MCB-0078264 to P.R.C., and MCB-9723661 and MCB-0117079 to J.H.G.).
PY - 2003/3/6
Y1 - 2003/3/6
N2 - 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+ [FA/FB]- backreaction indicate that in the mutant strains, plastoquinone-9 functions as the electron transfer cofactor in the A1 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.
AB - 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+ [FA/FB]- backreaction indicate that in the mutant strains, plastoquinone-9 functions as the electron transfer cofactor in the A1 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.
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U2 - 10.1016/S0005-2728(02)00396-1
DO - 10.1016/S0005-2728(02)00396-1
M3 - Article
C2 - 12615349
AN - SCOPUS:0037422396
SN - 0005-2728
VL - 1557
SP - 67
EP - 76
JO - Biochimica et Biophysica Acta - Bioenergetics
JF - Biochimica et Biophysica Acta - Bioenergetics
IS - 1-3
ER -