H-NOX from Clostridium botulinum, like H-NOX from Thermoanaerobacter tengcongensis, Binds Oxygen but with a Less Stable Oxyferrous Heme Intermediate

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• 作者：Gang Wu ; Wen Liu ; Vladimir Berka ; Ah-Lim Tsai
• 刊名：Biochemistry
• 出版年：2015
• 出版时间：December 8, 2015
• 年：2015
• 卷：54
• 期：48
• 页码：7098-7109
• 全文大小：539K
• ISSN：1520-4995

文摘

Heme nitric oxide/oxygen binding protein isolated from the obligate anaerobe Clostridium botulinum (Cb H-NOX) was previously reported to bind NO with a femtomolar K_D (Nioche, P. et al. Science 2004, 306, 1550鈥?/x>1553). On the other hand, no oxyferrous Cb H-NOX was observed despite full conservation of the key residues that stabilize the oxyferrous complex in the H-NOX from Thermoanaerobacter tengcongensis (Tt H-NOX) (the same study). In this study, we re-measured the kinetics/affinities of Cb H-NOX for CO, NO, and O₂. K_D(CO) for the simple one-step equilibrium binding was 1.6 脳 10^鈥? M. The K_D(NO) of Cb H-NOX was 8.0 脳 10^鈥?1 M for the first six-coordinate NO complex, and the previous femtomolar K_D(NO) was actually an apparent K_D for its multiple-step NO binding. An oxyferrous Cb H-NOX was clearly observed with a K_D(O₂) of 5.3 脳 10^鈥? M, which is significantly higher than Tt H-NOX鈥檚 K_D(O₂) = 4.4 脳 10^鈥? M. The gaseous ligand binding of Cb H-NOX provides another supportive example for the 鈥渟liding scale rule鈥?hypothesis (Tsai, A.-L. et al. Antioxid. Redox Signal. 2012, 17, 1246鈥?/x>1263), and the presence of hydrogen bond donor Tyr139 in Cb H-NOX selectively enhanced its affinity for oxygen.