title: 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.
abstract: 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 microE 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.
authors.affiliation: Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA. twj2@psu.edu
authors.forename: T
authors.initials: T
authors.lastname: Wade Johnson
authors.forename: Sushma
authors.initials: S
authors.lastname: Naithani
authors.forename: Charles
authors.initials: C
authors.lastname: Stewart
authors.forename: Boris
authors.initials: B
authors.lastname: Zybailov
authors.forename: A
authors.initials: A
authors.lastname: Daniel Jones
authors.forename: John H
authors.initials: JH
authors.lastname: Golbeck
authors.forename: Parag R
authors.initials: PR
authors.lastname: Chitnis
mesh_terms: D002851:Chromatography, High Pressure Liquid; D000458:Cyanobacteria / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D020868:Gene Silencing; D005798:Genes, Bacterial; D007652:Oxo-Acid-Lyases / Q000235:genetics* / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000032:analysis; D015183:Restriction Mapping; D013050:Spectrometry, Fluorescence / Q000379:methods; D013389:Succinate-CoA Ligases / Q000235:genetics* / Q000378:metabolism; D010837:Vitamin K 1 / Q000378:metabolism*
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D010837:Vitamin K 1; C060510:2-succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate synthase; D007652:Oxo-Acid-Lyases; D013389:Succinate-CoA Ligases; C022693:O-succinylbenzoate - CoA ligase