Selective cysteines oxidation in soluble guanylyl cyclase catalytic domain is involved in NO activation

Nitric oxide (NO) binds to soluble guanylyl cyclase (GC1) and stimulates its catalytic activity to produce cGMP. Despite the key role of the NO-cGMP signaling in cardiovascular physiology, the mechanisms of GC1 activation remain ill-defined. It is believed that conserved cysteines (Cys) in GC1 modulate the enzyme's activity through thiol-redox modifications. We previously showed that GC1 activity is modulated via mixed-disulfide bond by protein disulfide isomerase and thioredoxin 1. Herein we investigated the novel concept that NO-stimulated GC1 activity is mediated by thiol/disulfide switches and aimed to map the specific Cys that are involved. First, we showed that the dithiol reducing agent Tris (2-carboxyethyl)-phosphine reduces GC1 response to NO, indicating the significance of Cys oxidation in NO activation. Second, using dibromobimane, which fluoresces when crosslinking two vicinal Cys thiols, we demonstrated decreased fluorescence in NO-stimulated GC1 compared to unstimulated conditions. This suggested that NO-stimulated GC1 contained more bound Cys, potentially disulfide bonds. Third, to identify NO-regulated Cys oxidation using mass spectrometry, we compared the redox status of all Cys identified in tryptic peptides, among which, ten were oxidized and two were reduced in NO-stimulated GC1. Fourth, we resorted to computational modeling to narrow down the Cys candidates potentially involved in disulfide bond and identified Cys489 and Cys571. Fifth, our mutational studies showed that Cys489 and Cys571 were involved in GC1'response to NO, potentially as a thiol/disulfide switch. These findings imply that specific GC1 Cys sensitivity to redox environment is critical for NO signaling in cardiovascular physiology.

Abstract 869: Cysteine-based Redox Regulation of Soluble Guanylyl Cyclase

Soluble guanylyl cyclase (GC1) is the major receptor of nitric oxide (NO) and a key regulator for cardiovascular physiology. NO binding to the heme of GC1 catalyzes conversion of GTP to cGMP, which in turn activates protein kinase G pathway, thus leading to vasodilation. However, the mechanism by which NO signaling is propagated within the GC1 molecule for its stimulation is still poorly understood. The high frequency of solvent-exposed cysteines (Cys) of GC1 suggests a potential role of Cys posttranslational modifications (PTMs) in regulating GC1 activity. Our previous studies show that the disulfide reductase Thioredoxin 1 (Trx1) can interact with GC1 and affect its activity in cells. Together with studies showing that GC1 activity is modulated by thiol redox, we hypothesize that thiol/disulfide switch might be a mechanism that regulates the activity of GC1. Here we show that dithiol oxidant diamide can dose-dependently affect the activity of GC1. PEG-switch assay, LC/MS/MS and mutational analysis identified Cys involved in redox regulation of GC1. In addition, we show that Trx1 modulates Cys-based redox PTMs of GC1 in cells and blocking the interaction between Trx1 and GC1 affects GC1 activity in a purified system. Taken together, these results suggest that the thiol/disulfide switch of GC1 and its interaction with Trx1 could be an underlying mechanism for NO stimulation of GC1.

Synthesis, biological evaluation and docking of novel bisamidinohydrazones as non-peptide inhibitors of furin

A series of novel non-peptidicfurin inhibitors with values of inhibitory constants (Ki) in the range of 0.74-1.54 μM was obtained by interactions of aminoguanidine hydrocarbonate with three diaryldicarbalde- hydes. Correspondingly p-hydroquinone, piperazine and adipic acid were used as linkers between their ben- zene moieties. Docking studies of these new inhibitors into recently published 3D-structure of human furin (PDB code 4OMC) showed that they were able to interact with subsites S1 and S4 of the enzyme. The overall arrangement of bisamidinohydrazones into furin active site was similar to the position of the ligand co- crystallized with a protease. Observations obtained with molecular modeling allowed further guidance into chemical modifications of the synthesized inhibitors which improve their inhibitory activity.