Fig. 1. Sequence and structure of GluR6 chimeras.a, The molecular structure of GluR2 S1/S2 (Armstrong et al., 1999), with BETA 7,8 shown in red and the flip/flop region shown in green, is in accordance with thecolor scheme shown for the primary sequence below.b, GluR1 amino acids swapped into GluR6 are indicated with red and green lines for the following chimeras (GluR1 residue numbers are indicated in parentheses in the following and refer to the mature GluR1 protein):GluR6-BETA 7,8 (489–502), -Flip(722–781), -Helix J (742–752), -Helix K(750–763), and -FlipC17 (764–780). Structural elements of the GluR2 agonist-binding domain (Armstrong et al., 1999) are indicated in gray; horizontal bars represent α-helices, and arrows represent β-strands. Other symbols indicate residues known to be important in desensitization: the filled diamondindicates the amino acid that, when mutated, completely blocks desensitization [L507 in GluR3 (Stern-Bach et al., 1998)]; the filled triangle marks a site of glycosylation that is important for modulation by Concanavalin A of GluR6 desensitization (Everts et al., 1999); the filled square represents a residue thought to form an important exposed patch within a hydrophobic domain (Chen et al., 1999); andfilled circles indicate residues that differ as a result of alternative splicing within the flip/flop domain of GluR1 (Sommer et al., 1990). Residues in bold represent amino acids that are divergent between GluR1 and GluR6. c, Spatial relationship between GluR2 amino acids homologous to GluR1 residues S493 (within BETA 7,8), N750 (S750within GluR1 flip), and L479 [L507 of GluR3 (Stern-Bach et al., 1998)] is shown. This view of the molecule is rotated, with respect to a, to show better the side chains of residues used in this study. d, An identical view of the molecule is shown in a space-filling representation. The BETA 7,8 domain is shown in red, the flip/flop domain is shown in green, and the three critical residues are shown in pink. BETA 7,8, β-Strands 7 and 8; C, C terminal; N, N terminal.