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. Author manuscript; available in PMC: 2012 Dec 1.
Published in final edited form as: Curr Opin Genet Dev. 2011 Sep 28;21(6):740–746. doi: 10.1016/j.gde.2011.09.007

Figure 1. Autocatalytic clustering of GTP-Cdc42 by the Bem1 complex.

Figure 1

(A) A stochastically-activated GTP-Cdc42 on the membrane (viewed as en face snapshots) can recruit a Bem1 complex from the cytoplasm. The Bem1-associated GEF catalyzes conversion of neighboring GDP-Cdc42 into GTP-Cdc42, which can recruit more cytoplasmic Bem1 complexes, generating a positive feedback loop that “grows” a cluster of GTP-Cdc42. (B) Lateral diffusion of GTP-Cdc42 away from the cluster of Bem1 complexes (red gradient) followed by GTP hydrolysis, produces GDP-Cdc42. Conversely, lateral diffusion of GDP-Cdc42 into the cluster provides fresh substrate for the GEF, dynamically renewing the cluster. Because GTP-Cdc42 diffuses out at the same rate that GDP-Cdc42 diffuses in, the total (GTP- plus GDP-bound) Cdc42 concentration is uniform. (C) Simulation of the dynamic steady state illustrated in B. Color denotes concentration of the indicated species. See supplement for equations and methods.