Characterization of Two Different Five-Coordinate Soluble Guanylate Cyclase Ferrous–Nitrosyl Complexes

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• 作者：Emily R. Derbyshire ; Alexander Gunn ; Mohammed Ibrahim ; Thomas G. Spiro ; R. David Britt ; Michael A. Marletta
• 刊名：Biochemistry
• 出版年：2008
• 出版时间：March 25, 2008
• 年：2008
• 卷：47
• 期：12
• 页码：3892 - 3899
• 全文大小：1091K
• 年卷期：v.47,no.12(March 25, 2008)
• ISSN：1520-4995

文摘

Soluble guanylate cyclase (sGC), a hemoprotein, is the primary nitric oxide (NO) receptor in higher eukaryotes. The binding of NO to sGC leads to the formation of a five-coordinate ferrous−nitrosyl complex and a several hundred-fold increase in cGMP synthesis. NO activation of sGC is influenced by GTP and the allosteric activators YC-1 and BAY 41-2272. Electron paramagnetic resonance (EPR) spectroscopy shows that the spectrum of the sGC ferrous−nitrosyl complex shifts in the presence of YC-1, BAY 41-2272, or GTP in the presence of excess NO relative to the heme. These molecules shift the EPR signal from one characterized by g₁ = 2.083, g₂ = 2.036, and g₃ = 2.012 to a signal characterized by g₁ = 2.106, g₂ = 2.029, and g₃ = 2.010. The truncated heme domain constructs β1(1–194) and β2(1–217) were compared to the full-length enzyme. The EPR spectrum of the β2(1–217)−NO complex is characterized by g₁ = 2.106, g₂ = 2.025, and g₃ = 2.010, indicating the protein is a good model for the sGC−NO complex in the presence of the activators, while the spectrum of the β1(1–194)−NO complex resembles the EPR spectrum of sGC in the absence of the activators. Low-temperature resonance Raman spectra of the β1(1–194)−NO and β2(1–217)−NO complexes show that the Fe−NO stretching vibration of the β2(1–217)−NO complex (535 cm⁻¹) is significantly different from that of the β1(1–194)−NO complex (527 cm⁻¹). This shows that sGC can adopt different five-coordinate ferrous nitrosyl conformations and suggests that the Fe−NO conformation characterized by this unique EPR signal and Fe−NO stretching vibration represents a highly active sGC state.