Biology Reference
In-Depth Information
the molecular mechanism of the arrestin-receptor interaction much more
than about any other arrestin function, we still need a lot of additional infor-
mation to construct a perfect tool for therapeutic use.
Enhanced phosphorylation-independent versions of all arrestins have
been constructed
125-128
and shown to effectively desensitize several GPCRs
without receptor phosphorylation.
125,126,129
These mutants proved to be
useful in the studies of GPCR phosphorylation
129,130
and its role in partic-
ular biological processes.
130,167,168
However, wider practical use of
enhanced nonvisual arrestins, particularly for therapeutic purposes, is con-
tingent on our ability to make them target the receptors of our choosing,
rather than all GPCRs indiscriminately, like parental WT arrestin-2 and -3.
5.2. Constitutively monomeric arrestins
Self-association of arrestin-1 (known as S-antigen at the time) was discov-
ered even before its role in quenching rhodopsin signaling.
1
Arrestin-1 was
subsequently crystallized as a tetramer (dimer of dimers) by two independent
groups under different conditions.
17,18
It was shown to form dimers and tet-
ramers in solution by a variety of methods: analytical ultracentrifugation,
118
small angle X-ray scattering,
119
and multiangle light scattering.
120
The study
of arrestin-1 self-association using long-range measurements of inter-
subunit distances by DEER yielded an unexpected result; the solution
tetramer was found to be strikingly different from that in crystal form.
120
Elucidation of its structure
122
confirmed the earlier idea that arrestin-1 olig-
omers are storage forms.
118
It also explained the earlier finding that only
monomeric arrestin-1 can bind rhodopsin
120
; in the physiologically relevant
solution tetramer and both possible dimers the rhodopsin-binding surfaces of
all arestin-1 molecules are shielded by sister protomers.
122
Bovine, mouse, and human arrestin-1 were shown to self-associate via
the same monomer-dimer-tetramer equilibrium, although dimerization
and tetramerization constants were very different in these species.
121
Model-based targeted elimination of the same two phenylalanines generated
self-association-deficient bovine and mouse arrestin-1.
121,122
These results
showed that the structure of the solution tetramer of all mammalian
arrestin-1 is likely very similar, despite striking differences in dimerization
and tetramerization constants. This study also generated a constitutively
monomeric form of arrestin-1 that retained perfectly normal binding to rho-
dopsin and microtubules.
121
This mutant is the molecular tool necessary to
determine the biological role of robust arrestin-1 self-association at concen-
trations normally found in photoreceptors.
110,115-117
This is not a trivial
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