Guanine nucleotide dissociation stimulators

Fig. 1. ADP-ribosylafion of Rho by C3 transferases. Rho proteins are regulated by a GTPase cycle. The GTP-binding proteins ore inactive with GDP bound, and active in the GTP-bound form. GDP/GTP exchange is facilitated by guanine nucleotide dissociation stimulator(s) (GDS) and inhibited by guanine nucleotide dissociation inhibitor(s) (GDI). In the active form, Rho protein interacts with its effector(s) and induces several cellular responses, one of which is polymerization of actin. Rho is ADP-ribosylated by C3 transferases at asparagine-41. Most likely, the modification inhibits the interaction of Rho with its effector(s) which results in inhibition of Rho dependent processes (e.g. F-actin depolymerization)...

This in turn stimulates an exchange of bound GDP for GTP—that is, the dissociation of GDP from Gs, to be replaced by GTP (see here). A class of protein factors called guanine nucleotide exchange factors (GEF) assists in the exchange of GDP and GTP. 

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