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Polymers 2017, 9(11), 612; doi:10.3390/polym9110612

Binding of the GTPase Sar1 to a Lipid Membrane Monolayer: Insertion and Orientation Studied by Infrared Reflection–Absorption Spectroscopy

Institute of Chemistry, Physical Chemistry, Martin Luther University Halle-Wittenberg, 06099 Halle, Germany
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Received: 2 October 2017 / Revised: 26 October 2017 / Accepted: 6 November 2017 / Published: 14 November 2017
(This article belongs to the Special Issue From Amphiphilic to Polyphilic Polymers)
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Abstract

Membrane-interacting proteins are polyphilic polymers that engage in dynamic protein–protein and protein–lipid interactions while undergoing changes in conformation, orientation and binding interfaces. Predicting the sites of interactions between such polypeptides and phospholipid membranes is still a challenge. One example is the small eukaryotic GTPase Sar1, which functions in phospholipid bilayer remodeling and vesicle formation as part of the multimeric coat protein complex (COPII). The membrane interaction of Sar1 is strongly dependent on its N-terminal 23 amino acids. By monolayer adsorption experiments and infrared reflection-absorption spectroscopy (IRRAS), we elucidate the role of lipids in inducing the amphipathicity of this N-terminal stretch, which inserts into the monolayer as an amphipathic helix (AH). The AH inserting angle is determined and is consistent with the philicities and spatial distribution of the amino acid monomers. Using an advanced method of IRRAS data evaluation, the orientation of Sar1 with respect to the lipid layer prior to the recruitment of further COPII proteins is determined. The result indicates that only a slight reorientation of the membrane-bound Sar1 is needed to allow coat assembly. The time-course of the IRRAS analysis corroborates a role of slow GTP hydrolysis in Sar1 desorption from the membrane. View Full-Text
Keywords: Sar1; amphipathic helix; COPII; IRRAS; maximal insertion pressure; lipid monolayer Sar1; amphipathic helix; COPII; IRRAS; maximal insertion pressure; lipid monolayer
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Schwieger, C.; Meister, A.; Daum, S.; Blume, A.; Bacia, K. Binding of the GTPase Sar1 to a Lipid Membrane Monolayer: Insertion and Orientation Studied by Infrared Reflection–Absorption Spectroscopy. Polymers 2017, 9, 612.

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