The third and fourth transmembrane domains of Slc11a1: Comparison of their structures and positioning in phospholipid model membranes

Abstract

Interactions of two peptides TM3 and TM4, corresponding to the third and fourth transmembrane domains of a divalent metal-ion transporter Slc11a1, respectively, with phospholipid model membranes, including zwitterionic dimyristoylphosphatidylcholine (DMPC) and anionic dimyristoylphosphatidylglycerol (DMPG), are studied in a wide range of peptide-to-lipid (P:L) ratios, and the secondary structures and positioning of the peptides in the lipid bilayers are analyzed, using differential scanning calorimetry (DSC), circular dichroism (CD), and fluorescence techniques. DSC and fluorescence results indicate that both peptides are inserted in the phospholipid bilayers. TM4 is buried in the bilayers more deeply and the insertion position is less affected by pH values, whereas TM3 is less deeply embedded and the position is remarkably shifted toward the direction of the bilayer surface with increasing pH value. The incorporation of TM4 in both lipids causes more perturbation to the packing of the hydrophobic chains of the lipids than TM3. Moreover, the perturbation of TM3 to the lipid packing is pH dependent, whereas the perturbation of TM4 is less pH dependent but with an unusually larger change in the enthalpy of the main transition at pH 5.5 than those at pH 4 and 7. CD data demonstrate that the main discrimination between the secondary structures of TM4 and TM3 is the alpha-helix content, more helicity for TM4 than TM3 in both lipids. The folding of the peptides is also affected by the composition of the phospholipids. Anionic lipid DMPG induces more alpha-helical folding than neutral lipid DMPC for both peptides.

Structural insights into the transmembrane domains of human copper transporter 1

“…The spectra were scanned three times for each sample and averaged, and the blank was subtracted from all spectra. Final spectra were smoothed using a FFT filter, and the intensity was expressed as mean residue ellipticity . Secondary structure analysis was performed by CDPro software package .…”

Ion channel activity of transmembrane segment 6 of Escherichia coli proton‐dependent manganese transporter

“…The insertion position of TMS4 in the model membrane is affected less by pH than the position of TMS3. 38 These experiments have also demonstrated the importance of D192 located in TMS4 of Nramp2 for manganese binding. 37 Mutation at this position in Nramp2 (D192A) was previously shown to attenuate the uptake of cobalt and iron in cells.…”

“…31 Moreover, some unusual transport properties of Nramp proteins described previously can be interpreted in terms of channel-like mechanism. 15 So far, TMS3 and TMS4 of eukaryotic DMT1 (Nramp2) [32][33][34][35] and of eukaryotic Nramp1 [36][37][38] have been studied exclusively from the structural point of view. It has been shown that TMS4 of Nramp1 is buried more deeply in model lipid bilayers than TMS3.…”

Insight into the structures of the second and fifth transmembrane domains of Slc11a1 in membrane mimics

“…In our previous work, we have studied the structures and topologies of the peptides corresponding to the TMD1 and TMD6 of Slc11a2/DMT1 , TMD3 and TMD4 of Slc11a1 and some peptides from specific site mutations of these transmembrane domains in both organic solvents and detergent micelles using CD and NMR methods. We also studied the secondary structures and topologies of TMD1‐TMD5 of Slc11a1 in lipid membranes by CD and attenuated total reflectance (ATR) FTIR techniques.…”