Ligand-specific conformational changes in the alpha1 glycine receptor ligand-binding domain

TY - JOUR

T1 - Ligand-specific conformational changes in the alpha1 glycine receptor ligand-binding domain

AU - Pless, Stephan Alexander

AU - Lynch, Joseph W

PY - 2009/6/5

Y1 - 2009/6/5

N2 - Understanding the activation mechanism of Cys loop ion channel receptors is key to understanding their physiological and pharmacological properties under normal and pathological conditions. The ligand-binding domains of these receptors comprise inner and outer beta-sheets and structural studies indicate that channel opening is accompanied by conformational rearrangements in both beta-sheets. In an attempt to resolve ligand-dependent movements in the ligand-binding domain, we employed voltage-clamp fluorometry on alpha1 glycine receptors to compare changes mediated by the agonist, glycine, and by the antagonist, strychnine. Voltage-clamp fluorometry involves labeling introduced cysteines with environmentally sensitive fluorophores and inferring structural rearrangements from ligand-induced fluorescence changes. In the inner beta-sheet, we labeled residues in loop 2 and in binding domain loops D and E. At each position, strychnine and glycine induced distinct maximal fluorescence responses. The pre-M1 domain responded similarly; at each of four labeled positions glycine produced a strong fluorescence signal, whereas strychnine did not. This suggests that glycine induces conformational changes in the inner beta-sheet and pre-M1 domain that may be important for activation, desensitization, or both. In contrast, most labeled residues in loops C and F yielded fluorescence changes identical in magnitude for glycine and strychnine. A notable exception was H201C in loop C. This labeled residue responded differently to glycine and strychnine, thus underlining the importance of loop C in ligand discrimination. These results provide an important step toward mapping the domains crucial for ligand discrimination in the ligand-binding domain of glycine receptors and possibly other Cys loop receptors.

AB - Understanding the activation mechanism of Cys loop ion channel receptors is key to understanding their physiological and pharmacological properties under normal and pathological conditions. The ligand-binding domains of these receptors comprise inner and outer beta-sheets and structural studies indicate that channel opening is accompanied by conformational rearrangements in both beta-sheets. In an attempt to resolve ligand-dependent movements in the ligand-binding domain, we employed voltage-clamp fluorometry on alpha1 glycine receptors to compare changes mediated by the agonist, glycine, and by the antagonist, strychnine. Voltage-clamp fluorometry involves labeling introduced cysteines with environmentally sensitive fluorophores and inferring structural rearrangements from ligand-induced fluorescence changes. In the inner beta-sheet, we labeled residues in loop 2 and in binding domain loops D and E. At each position, strychnine and glycine induced distinct maximal fluorescence responses. The pre-M1 domain responded similarly; at each of four labeled positions glycine produced a strong fluorescence signal, whereas strychnine did not. This suggests that glycine induces conformational changes in the inner beta-sheet and pre-M1 domain that may be important for activation, desensitization, or both. In contrast, most labeled residues in loops C and F yielded fluorescence changes identical in magnitude for glycine and strychnine. A notable exception was H201C in loop C. This labeled residue responded differently to glycine and strychnine, thus underlining the importance of loop C in ligand discrimination. These results provide an important step toward mapping the domains crucial for ligand discrimination in the ligand-binding domain of glycine receptors and possibly other Cys loop receptors.

KW - Amino Acid Substitution

KW - Animals

KW - Binding Sites

KW - Cloning, Molecular

KW - DNA, Complementary

KW - Female

KW - Glycine

KW - Humans

KW - Kinetics

KW - Ligands

KW - Models, Molecular

KW - Oocytes

KW - Patch-Clamp Techniques

KW - Protein Conformation

KW - Receptors, Glycine

KW - Xenopus laevis

U2 - 10.1074/jbc.M809343200

DO - 10.1074/jbc.M809343200

M3 - Journal article

C2 - 19286654

SN - 0021-9258

VL - 284

SP - 15847

EP - 15856

JO - Journal of Biological Chemistry

JF - Journal of Biological Chemistry

IS - 23

ER -