• Another frequently observed situation is that of lipids sandwiched between neighboring
subunits. This is illustrated in Fig. 1.20 in the case of the tetrameric potassium channel
KcsA. In this particular case, the four lipids found at subunit/subunit interfaces are phosphatidylglycerol molecules (PG), a negatively charged phospholipid (see Fig. 1.1) whose presence
Fig. 1.16 Crystal structure of the photosynthetic reaction center from Thermochromatium tepidum
showing a bound phosphatidylethanolamine (PE) molecule. (A) The protein structure in ribbon representation, with the tryptophan residues and the bound PE (green and red) shown in space-filling representation. The location of the Trp residues and of the glycerol backbone of the bound PE molecule defines a
hydrophobic thickness of ~28 Å for the bilayer. (B) The PE molecule (in space-filling representation) and
the residues with which the lipid head group interacts. Note that these residues belong to two different
subunits, H and M (Figure from Lee 2003, # 2003 Elsevier B.V. All rights reserved. Original data from
Nogi et al. 2000, PDB file 1EYS).
Fig. 1.17 Binding sites for phosphatidylcholine (PC) on cytochrome c oxidase from Paracoccus
denitrificans. (A) Part of the transmembrane region of the protein, showing the two bound PC molecules.
On the periplasmic side (on top), salt bridges are formed between the phosphate and quaternary ammonium
in the lipid head group and, respectively, Arg-198 in subunit II and Asp-124 in subunit III of the oxidase.
(B) A view of the complex from the periplasm, showing how the PC molecules bind in deep grooves in the
transmembrane surface of the protein (Figure from Lee 2003, # 2003 Elsevier B.V. All rights reserved.
Original data from Iwata et al. 1995; Harrenga and Michel 1999, coordinates from PDB files 1QLE).
1.5 Membrane Protein/Lipid Interactions
27
subunits. This is illustrated in Fig. 1.20 in the case of the tetrameric potassium channel
KcsA. In this particular case, the four lipids found at subunit/subunit interfaces are phosphatidylglycerol molecules (PG), a negatively charged phospholipid (see Fig. 1.1) whose presence
Fig. 1.16 Crystal structure of the photosynthetic reaction center from Thermochromatium tepidum
showing a bound phosphatidylethanolamine (PE) molecule. (A) The protein structure in ribbon representation, with the tryptophan residues and the bound PE (green and red) shown in space-filling representation. The location of the Trp residues and of the glycerol backbone of the bound PE molecule defines a
hydrophobic thickness of ~28 Å for the bilayer. (B) The PE molecule (in space-filling representation) and
the residues with which the lipid head group interacts. Note that these residues belong to two different
subunits, H and M (Figure from Lee 2003, # 2003 Elsevier B.V. All rights reserved. Original data from
Nogi et al. 2000, PDB file 1EYS).
Fig. 1.17 Binding sites for phosphatidylcholine (PC) on cytochrome c oxidase from Paracoccus
denitrificans. (A) Part of the transmembrane region of the protein, showing the two bound PC molecules.
On the periplasmic side (on top), salt bridges are formed between the phosphate and quaternary ammonium
in the lipid head group and, respectively, Arg-198 in subunit II and Asp-124 in subunit III of the oxidase.
(B) A view of the complex from the periplasm, showing how the PC molecules bind in deep grooves in the
transmembrane surface of the protein (Figure from Lee 2003, # 2003 Elsevier B.V. All rights reserved.
Original data from Iwata et al. 1995; Harrenga and Michel 1999, coordinates from PDB files 1QLE).
1.5 Membrane Protein/Lipid Interactions
27