Lauric Acid receptor On the basis of the foregoing set of
On the basis of the foregoing set of considerations, L1 could exert three possible actions on sGC determining its deactivation, schematically depicted in Fig. 6: i) oxidation of Fe2+ to Fe3+; ii) coordination to sGC, conjecturably, via the pyridyl nitrogen of the canthin-6-one; iii) coordinating and/or reacting with Cys. This last process would deactivate sGC inhibiting the oxidative addition of NO to cysteine which, on the light of the Fernhoff et al. , would determine cysteine-assisted NO activation of sGC. Such reaction, consisting of a thiol S-nitrosation, requires a redox partner to act as an Lauric Acid receptor sink, and most often oxygen serves this role in vitro. Electrochemical data allow us to conclude that, deactivation of sGC by L1 in solution, involves the pathways ii) and iii), while pathway i) does not occur. This is supported by reported evidence on the formation of cysteine-quinone adducts . This coordination does not affect significantly the redox behavior of the Fe3+/Fe2+ couple, as described for myoglobin at cystein-modified electrodes . Then, the enhancement of cysteine-localized signal II can be assigned to an electrocatalytic effect exerted by L1, similarly to that described by Tan et al.  for the electrochemical oxidation of cysteine catalyzed by C60 fullerene. To better understand the interaction of L1 with the binding site of soluble guanylate cyclase, a molecular modeling study was performed. As the crystal structure of human sGC has not been resolved, the study started by constructing a 3D model using homology modeling. The search for templates of the b1-sGC domain was performed with the NCBI search domain algorithm  which identified the structure of the H-NOX Domain from T. tengcongensis (pdb code 1u55) as the possible possible candidate. The low sequence identity between both species (about 17%) implied a modeling exercise mainly qualitative in nature . Despite the far evolutionary relationship, sequence alignment provided by blast was rather good with only 3 inserts (the larger one being 3 amino acids long) and good agreement between the secondary structure motives of the templates and those of the β1-sGC (β1 soluble guanylate cyclase) target as predicted by several secondary structure prediction programs. In consequence, the homology modeling was carried out on the same alignment and performed using the Modeller interface included in the UCSF Chimera package (). Of the twenty models generated, only the one with lowest energy is here further analyzed. Not surprisingly, the best resulting model shows that a conserved tertiary structure with respect to the template. Only a slight rearrangement of the loop from residue 81 to residue 90 and corresponds to the insert region previously mentioned. Variations on the particular region of the binding site are far more noticeable and mainly characterized by a surprisingly wide distal cavity for sGC instead of the crowded center of the template; the volume of the distal pocket of the former reaches ca. of 568 A3 and while it does not overcome 14 A3 for the template (results obtained with the surfnet algorithm in UCSF Chimera . Our 3D model therefore suggests that sGC can accommodate substantially large organic compounds in its binding site and not only small diatomic molecules. Regarding the location of the cysteine residues – without doubt one of the most relevant aspects the modeling could bring to this work – the three of them Cys78, Cys122 and Cys174 occupies clearly differentiated locations on the structure (Fig. 8). While Cys78 stands in the distal cavity and on the top of one of the ethylenic substituents of the heme, the two others are located in the proximal region, far from the heme and mainly in regions exposed at the surface of the protein. Any direct or indirect oxidoreduction mechanism between Cys78, the heme and/or a chemical is plausible based on the 3D model while for the two other cysteine candidates only non direct interaction throughout a more complex cascade should be expected.