Fig. 4. Alignment of regions of the catalytic domain of selected guanylyl cyclases showing residues predicted to contact Mg-GTP. Homology modeling has been used to predict the residues (shaded) of soluble and receptor guanylyl cyclases that bind Mg-GTP (Liu et al., 1997). Sequences shown are the rat soluble guanylyl cyclase subunits 1, ß1 and ß2, the Manduca soluble subunits MsGC-1, MsGC-ß1 and MsGC-ß3, and the rat receptor guanylyl cyclase, GC-A. Light shading shows the residues from the chain and dark shading those from the ß chain. Note that the homodimeric guanylyl cyclases, rat ß2, GC-A and MsGC-ß3, possess all the residues from both and ß chains. *Residues mutated in MsGC-ß3E469K and MsGC-ß3R573Q.