Mohammed Ibrahim - Probing Soluble Guanylate Cyclase Activation by CO and YC-1 Using Resonance Raman Spectroscopy

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      Publication Details (including relevant citation   information):

      Biochemistry 2010, 49,   3815-3823.


      Soluble guanylate cyclase (sGC) is weakly activated by carbon   monoxide (CO) but is significantly activated by the binding of   YC-1 to the sGC−CO complex. In this report, resonance Raman (RR)   spectroscopy was used to study selected sGC variants. Addition of   YC-1 to the sGC−CO complex alters the intensity pattern of RR   bands assigned to the vinyl and propionate heme substituents,   suggesting changes in the tilting of the pyrrole rings to which   they are attached. YC-1 also shifts the RR intensity of the   νFeC and νCO bands from 473 and 1985   cm−1 to 487 and 1969 cm−1, respectively,   and induces an additional νFeC band, at 521   cm−1, assigned to five-coordinate heme-CO.   Site-directed variants in the proximal heme pocket (P118A) or in   the distal heme pocket (V5Y and I149Y) reduce the extent of YC-1   activation, along with the 473 cm−1 band intensity.   These lower-activity sGC variants display another νFeC  band at 493 cm−1 which is insensitive to YC-1 addition   and is attributed to protein that cannot be activated by the   allosteric activator. The results are consistent with a model in   which YC-1 binding to the sGC−CO complex results in a   conformational change that activates the protein. Specifically,   YC-1 binding alters the heme geometry via peripheral nonbonded   contacts and also relieves an intrinsic electronic effect that   weakens FeCO backbonding in the native, YC-1 responsive protein.   This electronic effect might involve neutralization of the heme   propionates via H-bond contacts or negative polarization by a   distal cysteine residue. YC-1 binding also strains the   Fe−histidine bond, leading to a population of the five-coordinate   sGC−CO complex in addition to a conformationally distinct   population of the six-coordinate sGC−CO complex. The loss of YC-1   activation in the sGC variants might involve a weakening of the   heme−protein contacts that are thought to be critical to a   YC-1-induced conformational change.

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