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. 2006 Feb 10;90(10):3375–3381. doi: 10.1529/biophysj.105.074898

FIGURE 1.

FIGURE 1

Lattice model for GroEL-GroES complex. (a) The closed GroEL-GroES compartment is modeled as a cage (red) connected by a hole (blue) to the open barrel, modeled as a box surrounded by a repulsive outer layer to avoid binding on the outside of the rim. The attractive internal lateral surface was represented by the strongly attractive and hydrophobic amino acid Phe (average pair interaction with the other amino acids, API = – 0.23 kT (see Eq. 6)), whereas a repulsive and hydrophilic back surface was made of Arg (API = 0.38 kT). The absolute system size is not a crucial physical parameter; in fact, what really matters is the ratio between the accessible volume inside the cage and the volume of the protein. For our model this value is ∼1.95, which is typical for the values found in experiments. (b) Space-filling representation of the x-ray structure of the GroEL-GroES-ADP complex (4). Colors represent the type of surface: all hydrophobic amino acids (A, V, L, I, M, F, P, and Y) are in yellow, and the polar ones (S, T, H, C, N, Q, K, R, D, and E) are in red. (c) Intermediate conformation during the extrusion process from the hydrophilic cage. If the inner surface of the closed GroEL-GroES compartment was made of the mildly hydrophobic Tyr (API = −0.16 kT), extrusion did not take place.