Structure/function of the soluble guanylyl cyclase catalytic domain

Abstract

Soluble guanylyl cyclase (GC-1) is the primary receptor of nitric oxide (NO) in smooth muscle cells and maintains vascular function by inducing vasorelaxation in nearby blood vessels. GC-1 converts guanosine 5′-triphosphate (GTP) into cyclic guanosine 3′,5′-monophosphate (cGMP), which acts as a second messenger to improve blood flow. While much work has been done to characterize this pathway, we lack a mechanistic understanding of how NO binding to the heme domain leads to a large increase in activity at the C-terminal catalytic domain. Recent structural evidence and activity measurements from multiple groups have revealed a low-activity cyclase domain that requires additional GC-1 domains to promote a catalytically-competent conformation. How the catalytic domain structurally transitions into the active conformation requires further characterization. This review focuses on structure/function studies of the GC-1 catalytic domain and recent advances various groups have made in understanding how catalytic activity is regulated including small molecules interactions, Cys-S-NO modifications and potential interactions with the NO-sensor domain and other proteins.

Instability in a coiled‐coil signaling helix is conserved for signal transduction in soluble guanylyl cyclase

“…How NO, CO, and effector compounds stimulate sGC catalytic activity remains unknown. For activation, binding of stimulatory compounds to the N‐terminal β1 H‐NOX domain must lead to optimal alignment of the two C‐terminal catalytic domains, which together form the active site . Possible mechanisms for this range from large‐scale conformational changes that release inhibitory domain contacts to subtle through‐protein adjustments that permit optimal cyclase domain alignment .…”

“…An attractive model in this regard is one in which, in the absence of a stimulatory signal, the coiled coil holds the cyclase domains in a misaligned orientation (Figure ). Such an orientation is easily imagined since cyclase domains alone, with the N‐terminal portions of the protein removed, display very low activity and have crystal structures with misaligned active sites . In this model, a change in coiled‐coil conformation, possibly with disruption of coiled‐coil packing, would serve to support optimal catalytic domain alignment and high levels of catalysis.…”

“…For activation, binding of stimulatory compounds to the N-terminal β1 H-NOX domain must lead to optimal alignment of the two C-terminal catalytic domains, which together form the active site. 38,39 Possible mechanisms for this range from large-scale conformational changes that release inhibitory domain contacts to subtle through-protein adjustments that permit optimal cyclase domain alignment. 5 Here, using a truncated form of sGC lacking cyclase domains, we show that the central coiled-coil helix regulates heme affinity for CO and appears to undergo a change in conformation upon CO binding that can be blocked by disulfide bond formation.…”

“…Such an orientation is easily imagined since cyclase domains alone, with the N-terminal portions of the protein removed, display very low activity and have crystal structures with misaligned active sites. 38,39,43,44 In this F I G U R E 6 Schematic for signal transduction through the coiledcoil domain. Stabilizing the coiled coil in Ms sGC-NT leads to lower CO affinity and higher melting temperature, while CO binding leads to a lower melting temperature.…”

Nitric oxide: To be or not to be an endocrine hormone?

“…The hormone‐like effects of NO are mostly mediated by its receptor, sGC, via sGC‐3,5‐cyclic guanosine monophosphate (cGMP)‐protein kinase G (PKG) pathway . Activated catalytic domain (αβGC cat ) of sGC converts GTP to cGMP; cGMP mediates physiological actions of NO by activating the downstream elements of the signalling pathway including PKG (I and II), cGMP‐gated cation channels and cGMP‐regulated phosphodiesterases (Figure ). Details about isoforms, structure and activity of sGC have been reviewed by Stasch et al and Horst et al…”