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Figure 4.
Figure 4. Interactions among the Three Components of the PP2A
Holoenzyme
(A) A surface potential representation of the
PP2A holoenzyme. The electrostatic surface potential is shown
for Aα and B′-γ1. Note the acidic environment at the
interface between Aα and B′-γ1. The carboxyl terminus of Cα
extends out into a negatively charged surface groove at the
interface between Aα and B′-γ1. Two areas are circled. Area
1 involves a protein interface between Cα and B′-γ1. Area 2
centers on the recognition of the carboxyl terminus of Cα by
Aα and B′-γ1.
(B) A stereo view of the atomic
interactions between Cα and B′-γ1 in area 1. This interface
involves the HEAT-like repeats 6–8 of B′-γ1 and the α5
helix region of Cα. Side chains are colored orange. This
interface contains a number of hydrogen bonds, which are
represented by red dashed lines.
(C) A stereo view of the
recognition of the carboxyl terminus of Cα by Aα and B′-γ1
in area 2. This interface involves the HEAT-like repeats 5 and 6
of B′-γ1 and HEAT repeats 1 and 2 of Aα. Most residues from
the carboxyl terminus of Cα participate in specific
interactions. There is a good mixture of hydrogen bonds and van
der Waals interactions at this interface.
(D) Additional
interactions with Cα are provided by the extended loop within
HEAT-like motif 2 of B′-γ1.
(E) A surface representation
of the PP2A holoenzyme to highlight the binding mode of the
regulatory B′/PR61 subunit. Note that B′-γ1 uses its convex
surface to interact with the conserved ridge of Aα.
(F) A
stereo view of the atomic interactions between Aα and B′-γ1.
This interface is rich in van der Waals interactions and
involves six HEAT repeats of Aα.
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