Figure 1.
Structural organization of guanylate cyclase.
A. Schematic depiction of domain organization of human guanylate cyclase. The native enzyme is a heterodimer of α and β subunits (encoded by GUCY1A3 and GUCY1B3, respectively), with interaction interfaces spread across the PAS, CC and cyclase catalytic domains. The catalytic domains associate in a head to tail orientation; conserved residues involved in substrate binding and catalysis are distributed between the two subunits. B. A list of conserved active-site residues in guanylate cyclase (sGCα and β) and in the chimeric adenylate cyclase (AC-V C1 domain and AC-II C2 domain). A full alignment of adenylate and guanylate cyclases is shown in Supporting Fig. S1.
Table 1.
Crystallographic statistics.
Table 2.
Guanylate cyclase activity of full-length and recombinant proteins.
Figure 2.
Overview of crystal structures.
A. Homodimer of sGCβ catalytic domain (PDB ID: 2WZ1). B. Heterodimer of sGCα (green) and sGCβ (cyan) catalytic domains (PDB ID: 3UVJ). C. Architecture of the sGCα catalytic domain. D. Architecture of the sGCβ catalytic domain. E. The β4–5 loop in AC-C1 (purple) and sGCα (green); the surface of the β/C2 subunit is shown in cyan.
Figure 3.
Structural transitions in sGC activation.
A. sGCα in the crystal structure (green) compared with the same subunit (orange) modelled by alignment with the C1 domain of adelylate cyclase (purple). The rigid-body transition involves a 26° rotation, seen in the relative angles of the corresponding α helices. B. Detail: the change in position of the α1 helix (sGCα), bringing it closer to helix α4 (sGCβ). C. Detail: shift in position of the β6–7 loop, which brings a catalyitic residue D530 closer to the position of the corresponding residue in AC(D440).
Figure 4.
Active site residues on sGC in the modelled active conformation.
The sGCα and sGCβ were separately aligned with AC domains C1 and C2, respectively. A. Overall view (the colour scheme is described in panel C). C. Active site residues surrounding an ATP analogue in the AC structure. C, D. Detailed views.
Figure 5.
A. Forskolin in its binding pocket in adenylate cyclase. B. The same region in sGC in the crystal structure: the cavity is collapsed, with no space for small-molecule binding. C. sGC in the modelled active conformation: a cavity opens up; although forskolin does not fit, other small molecules may occupy the site.