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K170
D290
D29
R169
D26
K11
R393
L100
D297
K10
L108
polar core
L104
1
23
4
678
9
5
Variable
Average
Conserved
3-element interaction
Figure 2.1 Functional conservation within the arrestin family. The sequences of true
arrestins were first aligned with Clustal Omega.
45
The multiprotein alignment was then
processed with the Consurf software.
46,47
Residue conservation among the aligned
members of the arrestin family was represented with PyMOL using the PDB 1ZSH crystal
structure of bovine b-arrestin 1 as the template and colored using the Consurf plugin for
PyMOL. The following sequences were used: human rod and cone arrestins and
b-arrestin 1 and 2; Drosophila melonogaster arrestins 1 and 2 and kurtz; Ciona intestinalis
BAB60819.1; Caenorhabditis elegans NP_508133. Sequences are colored from Bordeaux
red (highly conserved) to cyan (variable stretches). Full conservation of the amino acids
of the polar core and of the 3-element interaction domain (indicated as sticks) highlights
their conserved functional role.
(
Fig. 2.1
). Each module is about 150 amino acids long. This structure, which
includes 20
b
-strands and an
a
-helix, reveals two deeply curved sandwiches
related by a pseudo-twofold rotation axis, each made of two antiparallel
b
-sheets structured as fibronectin type III module.
48
The N-domain is made
of strands 1-10, strand 20, and helix 1, whereas the C-domain contains
strands 11-19.
3,5
The functionality of arrestins resides in their mode of recognition of acti-
vated receptors and the subsequent responses it triggers. The binding of
visual arrestin to phosphorylated rhodopsin follows a two-step mechanism.
First, a 3-element interaction cluster consisting of
b
-strand 1,
a
-helix 1, and
the C-tail senses the phosphorylation status of the receptor's cytoplasmic tail;
second, the breaking of a salt bridge within this 3-element interaction cluster
upon binding the phosphorylated receptor guides the phosphate groups in
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