Dictyostelium cGMP chemotaxis arm (guanylyl cyclases to GbpC to myosin II)

The cGMP second-messenger branch that controls myosin II and the cell-rear response during chemoattractant (cAMP) chemotaxis in Dictyostelium discoideum. On stimulation, two guanylyl cyclases — the membrane-bound GCA and the cytosolic soluble guanylyl cyclase sGC (sgcA) — produce a transient cGMP burst (the two are partly redundant; only the gca/sgc double mutant loses all cGMP). cGMP is then read out by GbpC, the large multidomain Roco-family protein that accounts for essentially all high-affinity soluble cGMP binding: cGMP binding to its cyclic-nucleotide-binding domains drives an intramolecular cascade (RasGEF -> Roc GTPase -> MAP3K-like kinase) whose output regulates myosin II heavy-chain phosphorylation and filament assembly at the cell rear, enabling retraction and polarity. Phrased over enzyme/effector functions and family selectors with D. discoideum representatives. OUT OF SCOPE: the parallel cGMP effector GbpD (a Rap1 GEF) and the Ca2+ channel IplA, the upstream chemoattractant relay (dicty_extracellular_camp_relay), and the precise in-vivo myosin-kinase substrate of GbpC (an unresolved question flagged in the gbpC review).

Dictyostelium-specific chemotaxis second-messenger module grounded to two guanylyl cyclases (GCA Q553Y7 and sGC/sgcA Q551V8, both GO:0004383) and the cGMP effector GbpC (Q8MVR1, GO:0030553). GO molecular-function terms were taken from the completed DICDI reviews; nodes use PANTHER family selectors plus D. discoideum representative members. The myosin II output is described in the effector role but not grounded as a separate node because GbpC's direct in-vivo kinase substrate is unresolved (see the gbpC review's suggested question). The parallel cGMP/Ca effectors GbpD and IplA are out of scope. Named to signal Dictyostelium scope so it does not collide with a generic cyclic-nucleotide signalling module.