Direct measurement of small ligand-induced conformational changes in the aspartate chemoreceptor using EPR.
Ligand-binding-induced conformational changes in the Salmonella typhimurium aspartate receptor were studied using spin-labeling electron paramagnetic resonance. Cysteine residues, introduced by site-directed mutagenesis at several positions in the aspartate receptor periplasmic domain, were used to attach covalently a thiol-specific spin label. The electron paramagnetic resonance spectra of these labeled proteins were obtained in the presence and absence of the ligand aspartate, and used to calculate the distance change between spin labels. The results support a model in which transmembrane signaling is executed by a combined movement of alpha helix 4 (which leads into transmembrane domain 2) relative to alpha helix 1 (connected to transmembrane domain 1), as well as a coming together of the two subunits. Ligand binding causes spin labels at position 39 and 179 (within one subunit) to move further from each other and spin labels at position 39 and 39' (between two subunits) to move closer to each other. Both of these changes are very small-less than 2.5 A. No similar changes were detected in any aspartate receptor samples solubilized in detergent, suggesting that the membrane is required for these conformational changes. This is the first case of physically measured ligand-induced changes in a full-length 1-2 transmembrane domain receptor, and the results suggest that very small ligand-induced movements can result in large effects on the activity of downstream proteins.
Ottemann
K M
KM
Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA.
Thorgeirsson
T E
TE
Kolodziej
A F
AF
Shin
Y K
YK
Koshland
D E
DE
D001224:Aspartic Acid / Q000378:metabolism*; D001426:Bacterial Proteins / Q000138:chemical synthesis / Q000737:chemistry* / Q000235:genetics; D002628:Chemoreceptor Cells; D003545:Cysteine / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D029968:Escherichia coli Proteins; D005998:Glycine / Q000235:genetics; D008024:Ligands; D008565:Membrane Proteins / Q000138:chemical synthesis / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding / Q000235:genetics; D011487:Protein Conformation; D011956:Receptors, Cell Surface; D012486:Salmonella typhimurium / Q000737:chemistry / Q000235:genetics; D013113:Spin Labels; D013912:Threonine / Q000235:genetics
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008024:Ligands; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D013113:Spin Labels; C057331:Tar protein, E coli; D013912:Threonine; D001224:Aspartic Acid; D003545:Cysteine; D005998:Glycine