NO rapidly mobilizes cellular heme to trigger assembly of its own receptor

Abstract

Nitric oxide (NO) signaling in biology relies on its activating cyclic guanosine monophosphate (cGMP) production by the NO receptor soluble guanylyl cyclase (sGC). sGC must obtain heme and form a heterodimer to become functional, but paradoxically often exists as an immature heme-free form in cells and tissues. Based on our previous finding that NO can drive sGC maturation, we investigated its basis by utilizing a fluorescent sGC construct whose heme level can be monitored in living cells. We found that NO generated at physiologic levels quickly triggered cells to mobilize heme to immature sGC. This occurred when NO was generated within cells or by neighboring cells, began within seconds of NO exposure, and led cells to construct sGC heterodimers and thus increase their active sGC level by several-fold. The NO-triggered heme deployment involved cellular glyceraldehyde-3-phosphate dehydrogenase (GAPDH)–heme complexes and required the chaperone hsp90, and the newly formed sGC heterodimers remained functional long after NO generation had ceased. We conclude that NO at physiologic levels triggers assembly of its own receptor by causing a rapid deployment of cellular heme. Redirecting cellular heme in response to NO is a way for cells and tissues to modulate their cGMP signaling and to more generally tune their hemeprotein activities wherever NO biosynthesis takes place.

Low levels of nitric oxide promotes heme maturation into several hemeproteins and is also therapeutic

“…While interactions of NO with marquee hemeproteins like soluble guanylate cyclase is known to cause activation [ 36 ], those with hemoglobin are known to cause scavenging of the NO [ [37] , [38] , [39] ]. While there are several other facets of NO hemeprotein relationship which are implicitly stated in the published literature, our earlier and current studies found that low NO doses trigger a rapid heme insertion into immature heme-free apo-sGCβ1, resulting in mature sGC heterodimer [ [40] , [41] , [42] ], and more examples of this low NO effect was clearly lacking. Whether this low NO phenomena is part of the NO-sGC signal pathway activation and whether other hemeproteins like globins also undergo such NO driven heme-insertion/maturation were largely unidentified.…”

Endothelial Dysfunction in Acute Hepatic Porphyrias

“…Concerning vascular physiology, the prosthetic heme of NO synthases (NOSs) is essential for dimerization of the enzyme subunits [ 52 , 53 ]. Additionally, it has been very recently shown that NO triggers intracellular heme redistribution to promote the assembly of its own receptors, the soluble guanylate cyclases (sGCs) which are heterodimeric hemoproteins themselves [ 54 , 55 ]. In the last few decades NO metabolism has been the subject of several investigations aimed at understanding the mechanisms of pathogenesis in AHPs [ 18 , 56 , 57 , 58 , 59 , 60 ].…”

Hsp90 in Human Diseases: Molecular Mechanisms to Therapeutic Approaches

“…Since our models for Hsp90 function in sGC and iNOS maturation are identical [50,51], it implies that Hsp90 may operate through a common mechanism to target and stabilize the heme-free forms of client hemeproteins, and then enable their maturation by driving heme insertion by an ATP-dependent process (Figure 3). Our past [20] and present [53] findings also revealed that low doses of nitric oxide (NO) can contribute to sGC maturation by triggering a rapid Hsp90-dependent heme insertion into the apo-sGCβ1 (heme-free) population, ultimately resulting in a mature sGC-α1β1 heterodimer [20]. This finding of an elevated active sGC-α1β1 heterodimer formation by a NO trigger causing heme-insertion into apo-sGCβ1, filled a void in an earlier work done by Ignarro and colleagues in the 1980s which showed that NO-heme moiety could be transferred into heme-free or apo-sGCβ1 through an exchange reaction with NO-hemeproteins to activate the enzyme [54].…”