Guanylyl cyclase domain

Fig. 6.3 Model ofthe domain structure ofthe natriuretic peptide receptor NPR, a receptor-type guanylyl cyclase. NPR is a dimeric transmembrane receptor which spans the membrane with two transmembrane elements. The extracytosolic domain comprises the ligand binding site and contains several disulfide bridges. The cytosolic part is composed of a kinase homology domain with multiple phosphorylation sites, an ATP binding site of unknown function and the catalytic guanylyl cyclase domain.

Soluble forms of guanylyl cyclase are activated by nitric oxide. These enzymes are homologous to the catalytic domains of the membrane-bound forms of GC. They are considered heterodimers because they appear to exist, under physiological conditions, as complexes of a and P subunits, each with Mr of 70-80 kDa. Both types of soluble GC contain three primary domains an amino-terminus heme domain responsible for binding nitric oxide (NO), a dimerization domain and a carboxy terminus catalytic domain. The aP heterodimer is required for enzyme activity [35]. This can be seen as similar to the situation for AC, which contains two catalytic entities within a single polypeptide chain (Fig. 21-5). 

CYCc Adenylyl/guanylyl cyclase, catalytic domain E(MF)B 1(1) 36(39) 1AB8... 

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