Crystal structure of the signaling helix coiled-coil domain of the β1 subunit of the soluble guanylyl cyclase

To investigate the structure of the CC S-helix region, we crystallized and determined the structure of the CC domain of the sGCβ1 subunit comprising residues 348-409. The crystal structure was refined to 2.15 ？ resolution.The CC structure of sGCβ1 revealed a tetrameric arrangement comprised of a dimer of CC dimers. Each monomer is comprised of a long a-helix, a turn near residue P399, and a short second a-helix. The CC structure also offers insights as to how sGC homodimers are not as stable as (functionally) active heterodimers via a possible role for inter-helix salt-bridge formation. The structure also yielded insights into the residues involved in dimerization. In addition, the CC region is also known to harbor a number of congenital and man-made mutations in both membrane and soluble guanylyl cyclases and those function-affecting mutations have been mapped onto the CC structure. This mutant analysis indicated an importance for not only certain dimerization residue positions, but also an important role for other faces of the CC dimer which might perhaps interact with adjacent domains. Our results also extend beyond guanylyl cyclases as the CC structure is, to our knowledge, the first S-helix structure and serves as a model for all S-helix containing family members.Mammalian guanylyl cyclases are key signaling proteins that produce the second messenger cGMP thereby regulating a variety of different processes such as vasodilation, diuresis, vision, and bone growth [1]. These cyclases are either membrane bound or are found as soluble forms. Members of the membrane guanylyl cyclases (mGC) include the atrial natriuretic peptide receptor (GC-A), heat-stable enterotoxin receptor (GC-C), and retinal guanylyl cyclases (GC-E and -F) whereas the soluble version is known as the soluble guanylyl cyclase (sGC). cGMP produced by these guanylyl cyclases activates downstream signaling proteins such as cGMP-dependent kinases and cGMP-dependent ion channels [2]. The cyclases are a