A structural Comparison of the N-Terminal Segment of the Apelin Receptor in Various Membrane Mimetics

Abstract

Membrane mimetics such as micelles, bicelles or bilayers provide an essential tool for studying membrane proteins and their fragments. In this study we present the structure of the N-terminal tail and first transmembrane segment of the apelin receptor (human APJ residues 1-55, APJ55). Using sodium dodecylsuphate (SDS), dodecylphosphocholine (DPC) and 1-palmitoyl-2-hydroxy-sn-glycero-3-phospho-(1′-rac-glycerol) (LPPG) alongside phospholipid bicelles, the structure of APJ55 is compared by both circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy. Far-UV CD spectroscopy demonstarates that APJ55 adopts a largely helical structure in each environment. Through 1H-15N HSQC NMR experiments, APJ55 is observed to be in similar though distinct conformations in SDS, DPC and LPPG micelles. The high-resolution structure of APJ55 in SDS micelles was solved and consists of a helix-kink-helix motif in the micelle-spanning transmembrane region. The solution-exposed N-terminal tail has several regions of converged structure. The structure and topology of APJ55 in SDS micelles is critically compared to those in DPC and LPPG micelles, and to low-resolution structural data in phospholipid bicelles, using solution- and solid-state NMR. Overall, this study provides important insight into the consistency of structures generated through different membrane mimetics.View Large Image | View Hi-Res Image | Download PowerPoint Slide