PMID: 8939703Oct 1, 1996Paper

Nonsteric factors dominate binding of nitric oxide, azide, imidazole, cyanide, and fluoride to the rhizobial heme-based oxygen sensor FixL

Chemistry & Biology
W C WinklerMarie-Alda Gilles-Gonzalez

Abstract

The FixL protein is a heme-based sensor. Binding of oxygen to a unique heme domain inhibits a kinase domain of the type found in two-component regulators. Oxygen association is slow, but the dissociation rate is comparable to that of myoglobins. We have probed the size and chemistry of the FixL heme pocket by measuring the affinites, on rates and off rates for a wide variety of ferric heme ligands. Cyanide, but not fluoride, regulates the kinase activity. To examine how the sensory heme domain interacts with the kinase, we asked how the presence of the kinase domain affects ligand binding. The affinities of ferric FixL for heme ligands follow the same trend as their pKa values: cyanide > 4-methyl imidazole > imidazole > fluoride > azide > thiocyanate. The association rates follow the reverse trend. Striking differences from myoglobin include a 6-fold greater affinity for, and faster binding to, the bulky ligand imidazole, a 14-fold faster on rate for nitric oxide, a 2 800-fold lower affinity for azide, and a complete failure to bind thiocyanate. The presence of the kinase domain does not alter the affinity or binding kinetics of the high-spin ligand fluoride, but affects the off rates of other ligands. The EPR spectrum shows a ...Continue Reading

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Citations

Sep 11, 2012·Biochemistry·Luciana HannibalDennis J Stuehr
Apr 14, 2006·Molecular Plant-microbe Interactions : MPMI·Fuyuko SasakuraMikiko Abe
Sep 25, 2002·Proceedings of the National Academy of Sciences of the United States of America·Ursula LieblMarten H Vos
Dec 23, 1998·Proceedings of the National Academy of Sciences of the United States of America·W GongM K Chan
Jun 9, 2005·Protein Expression and Purification·Christine SuquetJames D Satterlee
May 5, 1999·Current Opinion in Chemical Biology·K R Rodgers
Mar 15, 2013·Biochimica Et Biophysica Acta·Ursula LieblMarten H Vos
Oct 17, 2012·Biochemical and Biophysical Research Communications·Paolo AscenziFabio Polticelli
Apr 7, 2010·Molecular Plant-microbe Interactions : MPMI·Cristina SánchezMaría J Delgado
Sep 22, 2009·Biochemistry·Jason R TuckermanMarie-Alda Gilles-Gonzalez
Jan 6, 2018·Journal of the American Chemical Society·Mateusz ImiołekBenjamin G Davis

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