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

Study on peptide-peptide interactions between transmembrane domains of Slc11a1 in model membranes

In this study, we determined the interaction between TM4 and TM2/TM3 domain of Solute carrier family 11 member 1 (Slc11a1) by circular dichroism (CD) and fluorescence spectrum. The results indicated that, the cation transport process was likely to be accomplished by the collaboration of multiple TM domains rather than by TM4 domain alone. Therefore, this finding suggested possible transportation theory and be helpful to elucidate the mechanism of Slc11a1 in cation transport process.

Metal ion binding of the third and fourth domains of Slc11a1 in a model membrane

In this paper, differential scanning calorimetric (DSC) experiments have shown that the ability of third and fourth transmembrane domains of Slc11a1 to perturb DMPC model membranes is affected by metal ions.

Penetration of three transmembrane segments of Slc11a1 in lipid bilayers

Slc11a1 is a divalent metal cation transporter with 12 putative transmembrane domains (TM) and plays a role in host defense. In present work, we investigated the secondary structure and topology of the peptides associated to Slc11a1-TM2, TM3 and TM4 (wildtype peptides and function-relating mutants) in the phospholipid vesicles (DMPC, DMPG and their mixtures) using circular dichroism, fluorescence spectroscopy and differential scanning calorimetry. We found that TM3 is obviously different in secondary structure and topology from TM2 to TM4 in the lipid membranes. The peptide TM3 is less structured and embedded in the lipid membranes less deeply than TM2 and TM4 at pH 5.5 and 7. The insertion position of TM3 in the lipid membranes is adjusted by pH, more deeply at more acidic pH environment, whereas the locations of TM2 and TM4 in the lipid membranes are less changed with pH. The E139A substitution of TM3 significantly impairs the pH dependence of the buried depth of TM3 and causes a pronounced increase in helicity in all DMPG-containing lipid vesicles at pH 5.5 and 7 and in DMPC at pH 4. In contrast, TM2 and TM4 are similar in topology. The G169D mutation has little effect on the topological arrangement of TM4 in membranes. The property of headgroups of the phospholipids has an effect on the secondary structure and topology of the peptides. All peptides could be structured with more helicity and embedded more deeply in DMPG-containing lipid vesicles than in DMPC membrane at pH 5.5 and 7.

Structural insights into the transmembrane domains of human copper transporter 1

The human copper transporter 1 (hCtr1) mediates cellular uptake of copper and Pt-based chemotherapeutic anticancer drugs. In this paper, we determined the three-dimensional structure and oligomerization of the transmembrane domains (TMDs) of hCtr1 in 40% HFIP aqueous solution by using solution-state NMR spectroscopy. We firstly revealed that TMD1 forms an α-helical structure from Gly67 to Glu84 and is dimerized by close packing of its C-terminal helix; TMD2 forms an α-helical structure from Leu134 to Thr155 and is self-associated as a trimer by the hydrophobic contact of TMD2 monomers; TMD3 adopts a discontinuous helix structure, known as 'α-helix-coiled segment-α-helix', and is dimerized by the interaction between the N-terminal helices. The motif GxxxG in TMD3 is not fully involved in the helix, but partially unstructured as a linker between helices. The flexible linker of TMD3 may serve as a gating adapter to mediate pore on and off switch. The differences in the structure and aggregation of the TMD peptides may be related to their different roles in the channel formation and transport function.