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Figure 3.
Figure 3. Space filling representations of CaM binding regions.
Amino acid residues on the surface are labeled. Hydrophobic
residues of the CaM binding sequence are colored white, polar
residues yellow, negatively charged residues red, and positively
charged residues blue. Key amino acid residues for CaM binding
are labeled red. Hydrophobic residues from distant regions of
the primary sequence that have folded to participate in the
formation of the hydrophobic patch of the CaM binding region are
shown in translucent white. a, Ca^2+ insensitive CaM binding
region showing a hydrophobic patch flanked by predominantly
positively charged residues. This patch has a high degree of
complementarity to the target peptide binding surface of the CaM
globular domain, which has a hydrophobic patch flanked by
negatively charged residues. Such complementarity is believed to
be a critical factor in CaM−target peptide interactions.
Hydrophobic residues (Trp 268, Phe 277 and Phe 278) of protein
4.1R are known to be critical for CaM binding; replacement of
these residues with Ala greatly affects CaM binding. The point
mutation W268S results in CaM binding becoming Ca^2+ sensitive.
b, Ca^2+ sensitive CaM binding region showing a hydrophobic
patch and the distribution of charged residues. This region is
formed by an extended structure. The polar residue Ser 185 is
found to be important for Ca^2+ dependent interactions with CaM;
the mutation S185W increases the binding affinity between this
site and CaM and abolishes the Ca^2+ dependence.
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