NDLI: Met104 is the CO-replaceable ligand at Fe(II) heme in the CO-sensing transcription factor BxRcoM-1

Content Provider	Springer Nature Link
Author	Bowman, Hannah E. Dent, Matthew R. Burstyn, Judith N.
Copyright Year	2016
Abstract	Both Met104 and Met105 are involved, either directly or indirectly, in the redox mediated ligand switch of the heme-dependent transcription factor, RcoM-1. Recent studies of Burkholderia xenovorans RcoM identified Cys94 as the thiolate ligand in the Fe(III) state of the heme cofactor. Upon reduction, a neutral donor replaces Cys94 trans to His74. Homology modelling implicated either Met104 or Met105 as the possible ligand in the Fe(II) state. We spectroscopically compared wild type (WT) RcoM-1 to three Met-to-Leu variants (M104L, M105L, and M104L/M105L) to identify which Met residue acts as the ligand. All proteins were isolated as admixtures of Fe(III) and Fe(II)–CO heme; oxidation by ferricyanide enables study of homogeneous oxidation and coordination states. Met104 is the CO-replaceable Fe(II) heme ligand. The magnetic circular dichroism (MCD) spectrum of Fe(II) M105L resembled WT. M104L and M104L/M105L, however, showed spectra arising from the formation of a high-spin, five-coordinate species indicating the loss of the ligand. The electron paramagnetic resonance (EPR) spectra of WT Fe(III) RcoM-1, oxidized Fe(III) M104L, and as-isolated M105L exhibited narrow, rhombic low-spin signals typical of thiolate-bound hemes. In contrast, oxidized Fe(III) M105L and oxidized Fe(III) M104L/M105L revealed a broad, rhombic low-spin, six-coordinate signal indicative of replacement of the thiolate by a neutral ligand. Thus, we conclude that Met105 is important to the stability of the Fe(III) heme pocket during oxidation.
Starting Page	559
Ending Page	569
Page Count	11
File Format	PDF
ISSN	09498257
Journal	JBIC Journal of Biological Inorganic Chemistry
Volume Number	21
Issue Number	4
e-ISSN	14321327
Language	English
Publisher	Springer Berlin Heidelberg
Publisher Date	2016-06-09
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Carbon monoxide Electronic absorption spectroscopy Electron paramagnetic resonance Heme Magnetic circular dichroism spectroscopy Biochemistry Microbiology
Content Type	Text
Resource Type	Article
Subject	Biochemistry Inorganic Chemistry

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