Dynamic ligand exchange in soluble guanylyl cyclase (sGC): implications for sGC regulation and desensitization.
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.
Divisions of Hematology, University of Texas Health Science Center in Houston, Medical School, Houston, Texas 77030, USA. ah-lim.tsai@uth.tmc.edu
Ah-Lim
AL
Tsai
Vladimir
V
Berka
Iraida
I
Sharina
Emil
E
Martin
D000818:Animals; D002460:Cell Line; D006152:Cyclic GMP / Q000378:metabolism; D006162:Guanylate Cyclase / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D009569:Nitric Oxide / Q000378:metabolism*; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D000071756:Soluble Guanylyl Cyclase; D018411:Spodoptera
D018160:Receptors, Cytoplasmic and Nuclear; D009569:Nitric Oxide; D006418:Heme; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase; D006152:Cyclic GMP