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Ligand‐induced Conformational Changes in the Acetylcholine Binding Protein Analyzed by Hydrogen‐Deuterium Exchange Mass Spectrometry
Author(s) -
Shi Jianxin,
Komives Elizabeth A.,
Taylor Palmer
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a244-a
Subject(s) - chemistry , hydrogen–deuterium exchange , ligand (biochemistry) , protein subunit , epibatidine , stereochemistry , agonist , nicotinic acetylcholine receptor , ligand gated ion channel , crystallography , nicotinic agonist , biophysics , ion channel , receptor , mass spectrometry , biochemistry , chromatography , biology , gene
Recent X‐ray crystallographic studies of the acetylcholine binding protein (AChBP) have suggested that the C loop, found at the circumference of the pentameric molecule, shows distinctive conformational changes upon antagonist and agonist occupation of the protein. We have employed hydrogen‐deuterium exchange mass spectrometry to examine the influence of bound ligand on solvent exposure of AChBP in the presence of various ligands. Quantitative measurement of deuterium incorporation was possible for approximately 56% of the Lymnaea AChBP sequence, covering mostly the outer surface of AChBP. In the apo‐protein, two regions flanking the ligand occupation site at the subunit interface, C‐loop (175‐193) and F‐loop (165‐171), exchange rapidly. Other regions of the protein including the N‐ and C‐termini exchange slowly with solvent. Occupation by agonists, epibatidine and lobeline, and antagonists, methyllycaconitine, α‐bungarotoxin, and α‐cobratoxin, all markedly restrict the exchange of the C‐loop amide protons, though with different exchange rates and degree of exchange. This suggests that the C‐loop in the apo‐protein exhibits rapid fluctuations in an open conformation and the bound agonist or antagonist restricts solvent exposure through loop closure in the case of the agonists and through occlusion of solvent in the case of the larger antagonists. The F loop, found on the complementary subunit at the subunit interface, also reveals ligand selective changes in amide proton exchange rates. (Supported by NIH Grants P42‐ES10337 and R37‐GM18360).