title: Lipid-Protein Interactions in the Regulated Betaine Symporter BetP Probed by Infrared Spectroscopy.
abstract: The Na(+)-coupled betaine symporter BetP senses changes in the membrane state and increasing levels of cytoplasmic K(+) during hyperosmotic stress latter via its C-terminal domain and regulates transport activity according to both stimuli. This intriguing sensing and regulation behavior of BetP was intensively studied in the past. It was shown by several biochemical studies that activation and regulation depends crucially on the lipid composition of the surrounding membrane. In fact, BetP is active and regulated only when negatively charged lipids are present. Recent structural studies have revealed binding of phosphatidylglycerol lipids to functional important parts of BetP, suggesting a functional role of lipid interactions. However, a regulatory role of lipid interactions could only be speculated from the snapshot provided by the crystal structure. Here, we investigate the nature of lipid-protein interactions of BetP reconstituted in closely packed two-dimensional crystals of negatively charged lipids and probed at the molecular level with Fourier transform infrared (FTIR) spectroscopy. The FTIR data indicate that K(+) binding weakens the interaction of BetP especially with the anionic lipid head groups. We suggest a regulation mechanism in which lipid-protein interactions, especially with the C-terminal domain and the functional important gating helices transmembrane helice 3 (TMH3) and TMH12, confine BetP to its down-regulated transport state. As BetP is also activated by changes in the physical state of the membrane, our results point toward a more general mechanism of how active transport can be modified by dynamic lipid-protein interactions.
authors.affiliation: From the Goethe-University, Institute of Biophysics, Max-von-Laue-Strasse 1, D-60438, Frankfurt am Main, Germany.
authors.forename: Günnur
authors.initials: G
authors.lastname: Güler
authors.affiliation: Max Planck Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Strasse 3, D-60438, Frankfurt am Main, Germany, and.
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Gärtner
authors.affiliation: Max Planck Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Strasse 3, D-60438, Frankfurt am Main, Germany, and University of Regensburg, Faculty of Biology and Preclinical Medicine, Universitätsstrasse 31, D-93051, Regensburg, Germany Christine.Ziegler@biophys.mpg.de.
authors.forename: Christine
authors.initials: C
authors.lastname: Ziegler
authors.affiliation: From the Goethe-University, Institute of Biophysics, Max-von-Laue-Strasse 1, D-60438, Frankfurt am Main, Germany, maentele@biophysik.uni-frankfurt.de.
authors.forename: Werner
authors.initials: W
authors.lastname: Mäntele
mesh_terms: D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002308:Cardiolipins / Q000737:chemistry / Q000378:metabolism; D048230:Corynebacterium glutamicum; D003902:Detergents / Q000737:chemistry; D004789:Enzyme Activation; D005960:Glucosides / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000737:chemistry / Q000378:metabolism; D010716:Phosphatidylinositols / Q000737:chemistry / Q000378:metabolism; D011188:Potassium / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D055550:Protein Stability; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared; D027981:Symporters / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; C101652:BetP protein, Corynebacterium glutamicum; D002308:Cardiolipins; D003902:Detergents; D005960:Glucosides; D008051:Lipid Bilayers; D010446:Peptide Fragments; D010715:Phosphatidylglycerols; D010716:Phosphatidylinositols; D011994:Recombinant Proteins; D027981:Symporters; C040358:dodecyl maltoside; D011188:Potassium
keywords: BetP; activation; attenuated total reflection (ATR) FT-IR spectroscopy; infrared spectroscopy (IR spectroscopy); lipid bilayer; lipid-protein interaction; membrane lipid; osmoregulation; phospholipid; protein structure