Anaerobic chlorophyll isocyclic ring formation in Rhodobacter capsulatus requires a cobalamin cofactor

Simon P. Gough, Bent O. Petersen, Jens Øllgaard Duus

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The isocyclic ring of bacteriochlorophyll (BChl) is formed by the conversion of Mg-protoporphyrin monomethyl ester (MPE) to protochlorophyllide (PChlide), Similarities revealed by BLAST searches with the putative anaerobic MPE-cyclase BchE suggested to us that this protein also uses a cobalamin cofactor. We found that vitamin B-12 (B-12)-requiring mutants of the bluE and bluB genes of Rhodobacter capsulatus, grown without B-12, accumulated Mg-porphyrins. Laser desorption/ionization time-of-flight (LDI-TOF) MS and NMR spectroscopy identified them as MPE and its 3-vinyl-8-ethyl (mvMPE) derivative. An in vivo assay was devised for the cyclase converting MPE to PChlide, Cyclase activity in the B-12-dependent mutants required B-12 but not protein synthesis. The following reaction mechanism is proposed for this MPE-cyclase reaction. Adenosylcobalamin forms the adenosyl radical, which leads to withdrawal of a hydrogen atom and formation of the benzylic-type 13(1)-radical of MPE, Withdrawal of an electron gives the 13(1)-cation of MPE, Hydroxyl ion attack on the cation gives 13(1)-hydroxy-MPE. Withdrawal of three hydrogen atoms leads successively to 13(1)-keto-MPE, its 13(2)-radical, and cyclization to PChlide.
Original languageEnglish
JournalProceedings of the National Academy of Sciences of the United States of America
Volume97
Issue number12
Pages (from-to)6908-6913
ISSN0027-8424
DOIs
Publication statusPublished - 2000
Externally publishedYes

Keywords

  • Amino Acid Sequence
  • Anaerobiosis
  • Bacteriochlorophylls
  • Chromatography, Thin Layer
  • Cobamides
  • Iron
  • Molecular Sequence Data
  • Mutation
  • Oxygenases
  • Porphyrins
  • Rhodobacter capsulatus
  • Vitamin B 12
  • 13870-90-1 cobamamide
  • E1UOL152H7 Iron
  • EC 1.13.- Oxygenases
  • EC 1.14.13.- magnesium protoporphyrin monomethyl ester oxidative cyclase
  • P6YC3EG204 Vitamin B 12
  • bacteriochlorophyll
  • cobalamin
  • cyanocobalamin
  • protochlorophyllide
  • protoporphyrin
  • article
  • cyclization
  • desorption
  • enzyme activity
  • ionization
  • mass spectrometry
  • mutant
  • nonhuman
  • nuclear magnetic resonance spectroscopy
  • priority journal
  • protein synthesis
  • MULTIDISCIPLINARY
  • ESTER OXIDATIVE CYCLASE
  • NITROUS-OXIDE
  • BACTERIOCHLOROPHYLL-ALPHA
  • METHIONINE SYNTHASE
  • ESCHERICHIA-COLI
  • NMR-SPECTROSCOPY
  • PROTEINS
  • ENZYME
  • GENES
  • IDENTIFICATION
  • amino acid sequence
  • Purple Bacteria Anoxygenic Phototrophic Bacteria Eubacteria Bacteria Microorganisms (Bacteria, Eubacteria, Microorganisms) - Purple Nonsulfur Bacteria [08013] Rhodobacter capsulatus
  • adenosylcobalamin 13870-90-1
  • bacteriochlorophyll isocyclic ring
  • chlorophyll anaerobic isocyclic ring formation
  • cobalamin cofactor
  • magnesium-protoporphyrin monomethyl ester 15654-92-9
  • protochlorophyllide 20369-67-9
  • Rhodobacter capsulatus bluB gene
  • Rhodobacter capsulatus bluE gene
  • 03502, Genetics - General
  • 10060, Biochemistry studies - General
  • 10064, Biochemistry studies - Proteins, peptides and amino acids
  • 31000, Physiology and biochemistry of bacteria
  • 31500, Genetics of bacteria and viruses
  • Biochemistry and Molecular Biophysics
  • Genetics
  • COBALOXIMES

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