Specific Binding of CO to Tetraheme Cytochrome c₃

Abstract

Carbon monoxide (CO) has been identified as another bioactive molecule like NO. Binding of CO to a tetraheme cytochrome c(3) (cyt c(3)) was investigated using visible absorption spectroscopy, circular dichroism (CD), and NMR. CO was found to bind to the four hemes in different manners. CD spectra, however, indicated that only single-site CO binding can keep the protein intact. The K(d) for the single-site binding was 8.0 microM, which is a typical value for a CO sensor protein. Furthermore, NMR spectra of uniformly (15)N-labeled and specifically [(15)N]His-labeled proteins have provided evidence that CO specifically binds to the sixth coordination site of heme 2 via single-site binding. The CO-bound cyt c(3) could conduct redox reactions. In light of triheme cytochrome c(7), the CO-bound cyt c(3) may work as an electron transporter. It was reported for sulfate-reducing bacteria that CO can be used as an energy source and CO cycling is operating like H(2) cycling. Therefore, the CO-bound cyt c(3) may play a role in maintaining electron transport pathways on accumulation of toxic CO for its utilization.

Membrane Tetraheme Cytochrome cm552 of the Ammonia-Oxidizing Nitrosomonas europaea: A Ubiquinone Reductase

“…This is reminiscent of ligand binding to the tetraheme cyt c 554 , where a high-pH-induced form containing three low-spin hemes apparently reacts with CO and CN − (6). A similar result is observed for the tetraheme cyt c 3 that contains four low-spin hemes and each heme has a different K d for CO (48). These data suggest a relatively weak distal His-Fe bond in the low-spin hemes and that the hemes are accessible to solvent.…”

Whole-cell circular dichroism difference spectroscopy reveals an in vivo-specific deca-heme conformation in bacterial surface cytochromes

“…S11, ESI†), which is characteristic of the low-spin Fe 2+ state. These data suggest that the coordination of bis-histidine with the deca-hemes is maintained inside native MtrC as well as purified MtrC in the reduced state35–37 and has little effect on Soret CD peak intensity. Therefore, the CD signal decrease in reduced MtrC in native compared with purified system (Fig.…”

The HtrA/DegP family protease MamE is a bifunctional protein with roles in magnetosome protein localization and magnetite biomineralization

“…These motifs are known to bind haem covalently via thioether bonds between the cysteines of the CXXCH motif and the haem vinyl group, and are most commonly associated with c ‐type cytochromes (Bowman and Bren, 2008). c ‐type cytochromes have been shown to function in the oxidation and reduction of metals (Paquete and Louro, 2010) and to act as gas sensors (Takayama et al ., 2006). MamE could thus act in the reduction and/or oxidation of iron required for magnetite formation.…”