PDB file 1GP2
This file depicts a rat heterotrimeric inhibitory G Protein, with bound GDP. This structure was solved by M. A. Wall et al., in 1996.
Recommended display options:
Display as cartoon, and color chain, to distinguish the subunits a (chain a), b (chain b), g (chain g). To see the GDP, select hetero-ligand, display as spacefill, and color CPK.
The WD-repeat
in the b
subunit forms a sevenfold b
propeller.
Select protein-sheet
and specify a different color, to emphasize the b
structure.
Locate where
the ends of the b protein
overlap, with both ends of the protein segment contributing to one of the propeller blades.
Question:
Why
might this overlap of N and C-terminal ends of the protein have
evolved?
Examine the
domain of subunit a
that makes contact with subunit b
at the face of the b-propeller.
Select 200-215a
and color magenta.
This is the "switch II" domain of subunit a,
that changes position when GTP
replaces GDP, resulting in dissociation of Ga
from Gbg.
With your teammate at an adjacent computer, compare
this display of a-GDP
complexed to bg, and the one of a-GTP
(GTP analog). To facilitate this comparison, to make the b
& g subunits on this display disappear, use the
menu to select chain b
then select hide selected; then
select chain g and
hide selected. Rotate so
that both images have the same orientation in relation to the guanine ring and
first two phosphates of
GDP/GTP.
Compare
the position of switch II (should be colored magenta) with GDP and the GTP analog.
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