Structural Perspectives on the Mechanism of Soluble Guanylate Cyclase Activation

The enzyme soluble guanylate cyclase (sGC) is the prototypical nitric oxide (NO) receptor in humans and other higher eukaryotes and is responsible for transducing the initial NO signal to the secondary messenger cyclic guanosine monophosphate (cGMP). Generation of cGMP in turn leads to diverse physiological effects in the cardiopulmonary, vascular, and neurological systems. Given these important downstream effects, sGC has been biochemically characterized in great detail in the four decades since its discovery. Structures of full-length sGC, however, have proven elusive until very recently. In 2019, advances in single particle cryo–electron microscopy (cryo-EM) enabled visualization of full-length sGC for the first time. This review will summarize insights revealed by the structures of sGC in the unactivated and activated states and discuss their implications in the mechanism of sGC activation

Structural Perspectives on the Mechanism of Soluble Guanylate Cyclase Activation.

The enzyme soluble guanylate cyclase (sGC) is the prototypical nitric oxide (NO) receptor in humans and other higher eukaryotes and is responsible for transducing the initial NO signal to the secondary messenger cyclic guanosine monophosphate (cGMP). Generation of cGMP in turn leads to diverse physiological effects in the cardiopulmonary, vascular, and neurological systems. Given these important downstream effects, sGC has been biochemically characterized in great detail in the four decades since its discovery. Structures of full-length sGC, however, have proven elusive until very recently. In 2019, advances in single particle cryo-electron microscopy (cryo-EM) enabled visualization of full-length sGC for the first time. This review will summarize insights revealed by the structures of sGC in the unactivated and activated states and discuss their implications in the mechanism of sGC activation

Corrole-protein interactions in H-NOX and HasA.

Replacing the native porphyrin cofactor in haem proteins has led to the development of novel designer proteins for a variety of applications. In most cases, haem analogues bind in a way that is comparable to the iron porphyrin, but this is not necessarily the case for complexes bearing non-exchangeable ligands. This study probes how a P[double bond, length as m-dash]O corrole binds to functionally disparate hemoproteins: a haem-dependent oxygen sensor (H-NOX) and a haem-scavenging protein (HasA). The results demonstrate that the protein-cofactor interactions are distinct from the native, haem-bound holoprotein. In H-NOX, the P[double bond, length as m-dash]O unit primarily hydrogen bonds with the haem-ligating histidine (H102), rather than the hydrogen-bonding network that stabilises the Fe(ii)-O2 complex in the native protein. In the absence of H102, the protein is still able to bind the corrole, albeit at reduced levels. Molecular dynamics simulations were utilised to determine the flexibility of apo H-NOX and revealed the coupled motion of key residues necessary for corrole binding. In the case of HasA, the P[double bond, length as m-dash]O unit does not primarily interact with either the haem-ligating histidine (H32) or tyrosine (Y75). Instead, histidine 83, the hydrogen-bonding partner for Y75, is critical for P[double bond, length as m-dash]O corrole binding. The conformation of HasA is interrogated by site-specifically labelling the protein and exploiting Förster resonance energy transfer (FRET) to determine the dye-cofactor distance. HasA reconstituted with the P[double bond, length as m-dash]O corrole exhibits an extended, apo-like conformation. Together, these results demonstrate that non-natural cofactors can bind to proteins in unexpected ways and highlight the need to uncover these interactions for the further development of designer haem proteins

Structural insight into metallocofactor maturation in carbon monoxide dehydrogenase

© 2019 Wittenborn et al. Published under exclusive license by The American Society for Biochemistry and Molecular Biology, Inc. The nickel-dependent carbon monoxide dehydrogenase (CODH) employs a unique heterometallic nickel-iron-sulfur cluster, termed the C-cluster, to catalyze the interconversion of CO and CO2. Like other complex metalloenzymes, CODH requires dedicated assembly machinery to form the fully intact and functional C-cluster. In particular, nickel incorporation into the C-cluster depends on the maturation factor CooC; however, the mechanism of nickel insertion remains poorly understood. Here, we compare X-ray structures (1.50 -2.48 Å resolution) of CODH from Desulfovibrio vulgaris (DvCODH) heterologously expressed in either the absence (DvCODH-CooC) or presence (DvCODH-CooC) of co-expressed CooC. We find that the C-cluster of DvCODH-CooC is fully loaded with iron but does not contain any nickel. Interestingly, the so-called unique iron ion (Feu) occupies both its canonical site (80% occupancy) and the nickel site (20% occupancy), with addition of reductant causing further mismetallation of the nickel site (60% iron occupancy). We also demonstrate that a DvCODH variant that lacks a surface-accessible iron- sulfur cluster (the D-cluster) has a C-cluster that is also replete in iron but lacks nickel, despite co-expression with CooC. In this variant, all Feu is in its canonical location, and the nickel site is empty. This D-cluster- deficient CODH is inactive despite attempts to reconstitute it with nickel. Taken together, these results suggest that an empty nickel site is not sufficient for nickel incorporation. Based on our findings, we propose a model for C-cluster assembly that requires both CooC and a functioning D-cluster, involves precise redoxstate control, and includes a two-step nickel-binding process

Crystallographic Characterization of the Carbonylated A-Cluster in Carbon Monoxide Dehydrogenase/Acetyl-CoA Synthase

Copyright © 2020 American Chemical Society. The Wood-Ljungdahl pathway allows for autotrophic bacterial growth on carbon dioxide, with the last step in acetyl-CoA synthesis catalyzed by the bifunctional enzyme carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS). ACS uses a complex Ni-Fe-S metallocluster termed the A-cluster to assemble acetyl-CoA from carbon monoxide, a methyl moiety and coenzyme A. Here, we report the crystal structure of CODH/ACS from Moorella thermoacetica with substrate carbon monoxide bound at the A-cluster, a state previously uncharacterized by crystallography. Direct structural characterization of this state highlights the role of second sphere residues and conformational dynamics in acetyl-CoA assembly, the biological equivalent of the Monsanto process

Negative-Stain Electron Microscopy Reveals Dramatic Structural Rearrangements in Ni-Fe-S-Dependent Carbon Monoxide Dehydrogenase/Acetyl-CoA Synthase

© 2020 Elsevier Ltd Cohen et al. demonstrate that carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) undergoes wider conformational changes than previously reported. Furthermore, these new conformations explain how the ACS subunit can interact with corrinoid Fe-S protein (CFeSP) in order to mediate a methyl transfer reaction instrumental for anaerobic carbon fixation