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Figure 2.
FIG. 2. The  N1/ N2 extension of LARG.
a, structure of the N1/ N2 extension and its
contacts with the switch 1 region of RhoA. Side chains that
contribute to the small hydrophobic core of the extension are
shown except for Gln789 from 1, whose side-chain
packs against Trp-769. Several hydrogen bonds (dashed yellow
lines) also likely stabilize the extension: the side chain of
Glu-790 forms two backbone hydrogen bonds with the N terminus of
N1,
and a backbone carbonyl in the 2- 3 loop forms a hydrogen
bond with the side chain of Trp-769. The side chain of Gln-789
(not shown) also forms two backbone hydrogen bonds with the 2- 3 loop.
b, sequence alignment of the N1/ N2 extensions from Lbc
subfamily RhoGEFs, and comparison with the N-terminal extension
of Vav. Although they form distinct structures, the N1/ N2
extension of LARG and an analogous N-terminal extension of Vav
both appear to modulate RhoGEF activity (43). With respect to
LARG, intersectin has a two-residue deletion and several amino
acid substitutions in 1 (a glycine
substituted for Glu-790 and arginine substituted for Ile-786 in
LARG) that could potentially abrogate formation of an equivalent
extension. In the crystal structure of the intersectin-Cdc42
complex (42), only four of the residues corresponding to the
N-terminal extension (residues 1229-1232) were included in the
recombinant protein. Residues that contribute to the hydrophobic
core of the N1/ N2 extension are
colored orange, and those equivalent to LARG-Glu-790 are green.
The number preceding each sequence is the amino acid number of
the starting residue. GenBankTM GI numbers of sequences used for
the alignment are: LARG, 34395525; PDZ-RhoGEF, 34395516;
p115RhoGEF, 34395524; GEF-H1/Lfc, 6919894; Lbc, 6016482;
intersectin, 20141591; Net1, 16307475; Xpln, 9506401; Vav,
13124807.
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