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Figure 3.
Figure 3 Calpain has a unique N-terminal anchor. (A) The helical
anchor (residues 2 -16 are shown) makes contacts only with D-VI
(colors as in Figure 1). (B) View down the helical axis
highlights interactions between the residues in the anchor
(magenta type) and D-VI (black type), represented as an
electrostatic GRASP surface (Nicholls et al., 1991) (red,
acidic; blue, basic). (C) Side view of (B) illustrates the depth
of the hydrophobic pocket in D-VI, which interacts with
hydrophobic residues Ala2, Gly3, Ile4, Ala5, Leu8 and Ala9 of
the anchor. This anchor inhibits active site assembly by
associating with the regulatory subunit, thus restricting
flexibility of protease D-I. The anchor also acts as a
co-chaperone in concert with D-VI, ensuring proper folding of
the catalytic subunit. (B) and (C) were created with the program
GRASP (Nicholls et al., 1991).
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