Biomedical Engineering Reference
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and had substantially greater interaction with PhLP1 than Gb 3. The discrepancies
between these studies, and the latter with
in vitro
data (Dingus et al.
2005
) , could
result from differences in how the data were normalized, and the fact that Gb 4 is not
expressed well in cells compared to its expression
in vitro
(see Fig.
9.2
and associated
references). PhLP1 is present in reticulocyte lysates (Dingus and Hildebrandt, unpub-
lished observation), and preferential interaction with PhLP1 would help explain the
in vitro
studies demonstrating that Gb 1, G b4, and Gb2 bind to CCT better than does
Gb3 (Wells et al.
2006
) . G b5 in particular has a reduced interaction with PhLP1
(Howlett et al.
2009
), which correlates to the observed poor interaction of Gb 5 with
CCT
in vitro
(Dingus et al.
2005
). In fact, it was suggested that the role of PhLP1 in
the co-chaperoning of Gb5 is different than for other Gb isoforms (Howlett et al.
2009
), in agreement with the idea that factors involved in dimer formation differen-
tially effect the Gb subunit isoforms (Dingus et al.
2005
) .
9.12
A Model for Folding of G b and the Formation
of Gb g Dimers
A working model for the synthesis and assembly of Gb g dimers is shown in Fig.
9.5
.
The following comments about this model are related to the numbers in the figure.
In some cases there are several possible mechanisms associated with a step, as for
Fig. 9.5
Working model for the synthesis and assembly of Gb g dimers.
Numbers in
green
are
discussed in the text. (
1
). Synthesis of G protein subunits. (
2
). Association of Gb with CCT. (
3
).
Process of folding and release of Gb and PhLP1 from CCT. Various scenarios are discussed in the
text about the details of this process. (
4
). Process of dimer formation and possible role(s) of
DRiP78. (
5
). Prenylation, membrane association and heterotrimer formation
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