The Selectivity of Vibrio cholerae H-NOX for Gaseous Ligands Follows the “Sliding Scale Rule” Hypothesis. Ligand Interactions with both Ferrous and Ferric Vc H-NOX
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- 作者：Gang Wu ; Wen Liu ; Vladimir Berka ; Ah-lim Tsai
- 刊名：Biochemistry
- 出版年：2013
- 出版时间：December 31, 2013
- 年：2013
- 卷：52
- 期：52
- 页码：9432-9446
- 全文大小：680K
- ISSN：1520-4995
文摘
Vc H-NOX (or VCA0720) is an H-NOX (heme-nitric oxide and oxygen binding) protein from facultative aerobic bacterium Vibrio cholerae. It shares significant sequence homology with soluble guanylyl cyclase (sGC), a NO sensor protein commonly found in animals. Similar to sGC, Vc H-NOX binds strongly to NO and CO with affinities of 0.27 nM and 0.77 渭M, respectively, but weakly to O2. When positioned on a 鈥渟liding scale鈥?plot [Tsai, A.-l., et al. (2012) Biochemistry 51, 172鈥?86], the line connecting log KD(NO) and log KD(CO) of Vc H-NOX can almost be superimposed with that of Ns H-NOX. Therefore, the measured affinities and kinetic parameters of gaseous ligands to Vc H-NOX provide more evidence to validate the 鈥渟liding scale rule鈥?hypothesis. Like sGC, Vc H-NOX binds NO in multiple steps, forming first a six-coordinate heme鈥揘O complex at a rate of 1.1 脳 109 M鈥? s鈥?, and then converts to a five-coordinate heme鈥揘O complex at a rate that is also dependent on NO concentration. Although the formation of oxyferrous Vc H-NOX cannot be detected at a normal atmospheric oxygen level, ferrous Vc H-NOX is oxidized to the ferric form at a rate of 0.06 s鈥? when mixed with O2. Ferric Vc H-NOX exists as a mixture of high- and low-spin states and is influenced by binding to different ligands. Characterization of both ferric and ferrous Vc H-NOX and their complexes with various ligands lays the foundation for understanding the possible dual roles in gas and redox sensing of Vc H-NOX.