Biophysical Society Thematic Meeting | Ascona, Switzerland

Liposomes, Exosomes, and Virosomes: From Modeling Complex Membrane Processes to Medical Diagnostics and Drug Delivery

Poster Abstracts

60-POS Board 30 In Vitro Folding of the Membrane Transporter Leut in Detergent and Lipid Bilayer Environments Michael Sanders , Heather Findlay, Paula Booth. King's College, London, United Kingdom. Little is understood about the process that governs the folding of multi domain α-helical integral membrane proteins from an amino acid sequence to a three dimensional functional structure[1]. The neurotransmitter sodium symporter (NSS) protein family is an example of α-helical transporter proteins. The NSS family encompasses a wide range of prokaryotic and eukaryotic ion-coupled transporters that regulate the transport of neurotransmitter molecules whose dysfunction has been implicated in several neurological and psychiatric disorders [2]. The prokaryotic orthologue of the NSS family LeuT comes from the organism Aquifex aeolicus. LeuT is responsible for the uphill transport of Leucine as a part of a symport mechanism driven by a sodium electrochemical gradient. In Vitro folding of α-helical membrane proteins has been studied mostly within protein detergent complexes or unfolded protein has been refolded into a lipid bilayer [3]. Here we exploit reversible chemical unfolding to determine the unfolding free energy of LeuT both as part of a protein-detergent complex and within a lipid bilayer. In dodecyl maltoside micelles, LeuT reversibly unfolds in Urea, whereas in a lipid bilayer LeuT only reversibly unfolds in the presence of both Urea and the nonionic detergent Octyl-β-Glucoside without physically changing the state of the lipid bilayer. Chemical denaturation causes a significant reduction in the α-helical content and loss of transport activity, full recovery of helical content and substrate transport occurs when the denaturants are removed allowing the free energy to be determined. This study gives insight into the comparative free energy landscape of protein folding between detergent and lipid environments as well as the effect of protein-lipid interactions on membrane protein function and stability.

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