Abstract
Accumulating evidence indicates that the functional properties of soluble guanylyl cyclase (sGC) are affected not only by the binding of NO but also by the NO:sGC ratio and a number of cellular factors, including GTP. In this study, we monitored the time-resolved transformations of sGC and sGC-NO complexes generated with stoichiometric or excess NO in the presence and absence of GTP. We demonstrate that the initial five-coordinate sGC-NO complex is highly activated by stoichiometric NO but is unstable and transforms into a five-coordinate sGC-2 state. This sGC-2 rebinds NO to form a low activity sGC-NO complex. The stability of the initial complex is greatly enhanced by GTP binding, binding of an additional NO molecule, or substitution of βHis-107. We propose that the transient nature of the sGC-NO complex, the formation of a desensitized sGC-2 state, and its transformation into a low activity sGC-NO adduct require βHis-107. We conclude that conformational changes leading to sGC desensitization may be prevented by GTP binding to the catalytic site or by binding of an additional NO molecule to the proximal side of the heme. The implications of these observations for cellular NO/cGMP signaling and the process of rapid desensitization of sGC are discussed in the context of the proposed model of sGC/NO interactions and dynamic transformations.
Highlights
The enzyme soluble guanylyl cyclase converts the NO signal into cGMP
The goal of this study was to investigate the dynamics of NO interaction with soluble guanylyl cyclase (sGC) and the functional outcome of such interaction
The green path illustrates what happens under conditions of stoichiometric NO, the blue path reflects the processes occurring in the presence of GTP, and the red path shows the behavior of sGC when NO is in excess
Summary
The enzyme soluble guanylyl cyclase (sGC) converts the NO signal into cGMP. Results: Stoichiometric NO forms an unstable sGC-NO complex, which is stabilized by extra NO, GTP, or substitution of His-107. We demonstrate that the initial five-coordinate sGC-NO complex is highly activated by stoichiometric NO but is unstable and transforms into a five-coordinate sGC-2 state. We conclude that conformational changes leading to sGC desensitization may be prevented by GTP binding to the catalytic site or by binding of an additional NO molecule to the proximal side of the heme. The implications of these observations for cellular NO/cGMP signaling and the process of rapid desensitization of sGC are discussed in the context of the proposed model of sGC/NO interactions and dynamic transformations
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