Generic GTPase nucleotide switch motif (GEF / GTP / GAP)

The minimal, reusable nucleotide-switch motif shared by regulatory GTPases: a guanine-nucleotide exchange factor (GEF) loads GTP to flip the GTPase into its active conformation, where it engages downstream effectors; a GTPase-activating protein (GAP) then stimulates GTP hydrolysis to return the switch to its inactive GDP-bound state. The motif is deliberately gene-free and taxon-neutral: it fixes only the GEF/GTPase/GAP roles (by molecular-function term) and the load/hydrolyze topology. Concrete switches - the Ras, Rho/Rac/Cdc42, Rab, Arf, Ran, and heterotrimeric-Galpha families - embed this motif as an inner bundle through `conforms_to`, substituting their own GEF/GTPase/GAP and the specific effectors they activate. Grounded in GO:0007264 (small GTPase-mediated signal transduction).

Reusable conformance target. A node in a concrete pathway declares `conforms_to: [{template: gtpase_switch}]` when its steps instantiate the GEF-load / active-GTPase / GAP-hydrolyze switch. The Ras switch inlined in MODULE:erk_cascade is one realization. Participants are abstract selectors because the motif asserts the switch chemistry only, so the module takes no gene members: concrete GTPases attach through `conforms_to` on their own pathway module, never as members here. Scope caveat: the motif requires a *trans*-acting GEF and GAP as separate gene products. Polymerizing GTPases of the tubulin/FtsZ superfamily (including archaeal CetZ) and the dynamin superfamily are therefore out of scope even though they carry GO:0003924 - their nucleotide cycle is driven by assembly, with hydrolysis activated in trans by the adjacent protomer at the polymer interface and exchange occurring spontaneously on free subunits, rather than by dedicated GEF and GAP proteins.