Nitric Oxide and Heat Shock Protein 90 Activate Soluble Guanylate Cyclase by Driving Rapid Change in Its Subunit Interactions and Heme Content

Background: Heme insertion into souble guanylate cyclase (sGC) enables it to bind nitric oxide (NO) for cell signaling. Results: NO triggered a rapid, reversible, and hsp90-dependent heme insertion into sGC-1 and an association with sGC-1 subunit. sGC activator BAY 60-2770 did the same. Conclusion: NO dynamically impacts the maturation and stability of active sGC heterodimer. Significance: The data uncover new mechanisms that regulate cellular NO signaling cascades. The chaperone heat shock protein 90 (hsp90) associates with signaling proteins in cells including soluble guanylate cyclase (sGC). hsp90 associates with the heme-free (apo) sGC-1 subunit and helps to drive heme insertion during maturation of sGC to its NO-responsive active form. Here, we found that NO caused apo-sGC-1 to rapidly and transiently dissociate from hsp90 and associate with sGC-1 in cells. This NO response (i) required that hsp90 be active and that cellular heme be available and be capable of inserting into apo-sGC-1; (ii) was associated with an increase in sGC-1 heme content; (iii) could be mimicked by the heme-independent sGC activator BAY 60-2770; and (iv) was followed by desensitization of sGC toward NO, sGC-1 disassociation, and reassociation with hsp90. Thus, NO promoted a rapid, transient, and hsp90-dependent heme insertion into the apo-sGC-1 subpopulation in cells, which enabled it to combine with the sGC-1 subunit to form the mature enzyme. The driving mechanism likely involves conformational changes near the heme site in sGC-1 that can be mimicked by the pharmacologic sGC activator. Such dynamic interplay between hsp90, apo-sGC-1, and sGC-1 in response to NO is unprecedented and represent new steps by which cells can modulate the heme content and activity of sGC for signaling cascades.