Assignment of the hyperfine-shifted 1H-NMR signals of the heme in the oxygen sensor FixL from Rhizobium meliloti

Craig Bertolucci, Li June Ming, Gonzalo Gonzalez, Marie A. Gilles-Gonzalez

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Background: The Rhizobial oxygen sensor FixL is a hemoprotein with kinase activity. On binding of strong-field ligands, a change of the ferrous or ferric heme iron from high to low spin reversibly inactivates the kinase. This spin-state change and other information on the heme pocket have been inferred from enzymatic assays, absorption spectra and mutagenesis studies. We set out to investigate the spin-state of the FixL heme and to identify the hyperfine-shifted heme-proton signals by NMR spectroscopy. Results: Using one-dimensional NMR we directly observed the high- and low-spin nature of the met- and cyanomet-FixL heme domain, respectively. We determined the hyperfine-shifted 1H-NMR signals of the heme and the proximal histidine by one- and two-dimensional spectroscopy and note the absence of distal histidine signals. Conclusions: These findings support the spin-state mechanism of FixL regulation. They establish that the site of heme coordination is a histidine residue and strongly suggest that a distal histidine is absent. With a majority of the heme resonances identified, one- and two-dimensional NMR techniques can be extended to provide structural and mechanistic information about the residues that line the heme pocket.

Original languageEnglish (US)
Pages (from-to)561-566
Number of pages6
JournalChemistry and Biology
Issue number7
StatePublished - Jul 1996


  • FixL
  • NMR
  • myoglobin
  • nitrogen fixation
  • sensor kinase

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Medicine
  • Molecular Biology
  • Pharmacology
  • Drug Discovery
  • Clinical Biochemistry


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