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Figure 8.
Particular Gα selectivity determinants inferred from the
structural model of the triple mutant RGS2(C106S,N184D,E191K)
bound to Gα[i3].A, illustration of the αVII–αVIII region of
the RGS domain to highlight the intramolecular interaction
between the highly conserved αVIII helix arginine (Arg^188 of
RGS2) and position 184 (asparagine in wild type RGS2 and
aspartate in the triple mutant). RGS2(C106S,N184D,E191K) triple
mutant (yellow-green; PDB code 2V4Z), unliganded wild type RGS2
(gray; PDB code 2AF0), and the Gα[i1]-bound RGS16 (dark green;
PDB code 2IK8) were aligned by sequence and then structure (Cα
atoms) using the Align command with default align settings of
MacPyMOL (DeLano Scientific, Palo Alto, CA), resulting in root
mean square deviations of 0.92 and 0.80 Å, respectively.
The conserved Arg^188 makes salt bridges with the terminal
oxygens of the Asp^184 side chain in the RGS2(C106S,N184D,E191K)
mutant and the analogous asparate side chain in RGS16; however,
only one contact can be made between Arg^188 and the Asn^184
side chain of wild type RGS2. Loss of the second salt bridge
creates a torsion in the wild type RGS2 Asp^184 residue,
resulting of the loss of the stabilizing hydrogen bond to
Thr^182 in switch I of the Gα subunit. B, critical contacts
between the three mutated positions of RGS2(C106S,N184D,E191K)
(yellow-green) and its Gα binding partner (Ras-like domain in
red; all-helical domain in blue; switch regions in cyan; bound
GDP in magenta). The modeled terminal atoms of the Lys^191 side
chain (spheres) within RGS2(C106S,N184D,E191K) are in close
enough proximity to make a hydrogen bond with Glu^65 of the Gα
all-helical domain. Asp^184 makes two hydrogen bonds with
Arg^188 and an additional bond with the backbone amine of the
peptide bond connecting Thr^181 and Thr^182, both located within
switch I of Gα. Ser^106 of the RGS2 triple mutant is tightly
packed with the backbone carbonyl and γ-hydroxyl of Gα
Thr^182, both being less than 3.9 Å from β-carbon of
Ser^106. Additionally, the Gα switch II residue Lys^210 is 3.8
Å from the Ser^106 α-carbon.
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