Comparison of the crystallographic structures of various cytochrome c oxidases indicates that
lipid-binding sites can be conserved in the course of evolution and that, in detergent-solubilized
oxidases, detergent alkyl chains may substitute to lipid acyl chains (Qin et al. 2006, 2007)
(Fig. 1.22) (see also Tsukihara et al. 1996; Shinzawa-Itoh et al. 2007, for cytochrome c oxidase, and
Palsdottir and Hunte 2004; Wenz et al. 2009; Vinothkumar 2011, for similar observations with the
cytochrome bc 1 complex and bacterial GlpG). Examples of the same region on the protein surface
being occupied by a hydrophobic chain in parallel MD simulations carried out either in a lipid or in a
detergent environment have also been reported (see e.g. Rouse and Sansom 2015).
What these observations point to is that lipids should not be regarded as a featureless
two-dimensional solvent, whose bulk physical properties only should be taken into consideration
when considering their effects on integral MPs. Many of them bind at defined positions at the TM
Fig. 1.21 Lipids in the Photosystem I reaction center supertrimer from the thermophilic cyanobacterium
Synechococcus elongatus. (A) Overall view of the supertrimer in projection on the plane of the membrane.
Dashed lines mark the approximate limits of a supermonomer, a black triangle the threefold symmetry
axis. (B) Overall view of a supermonomer, showing only the cofactors and lipids (the side chains of the
antenna chlorophyll a molecules have been omitted). The four lipids are in turquoise: PG phosphatidylglycerol, MGDG monogalactosyl diglyceride. (C) Details of the liganding of the magnesium atom of a
chlorophyll a molecule by the phosphate group of PG III (Adapted from Jordan et al. 2001. # 2001
Macmillan Publishers Limited, Nature. All rights reserved).
30
1 Membrane Proteins and Their Natural Environment
lipid-binding sites can be conserved in the course of evolution and that, in detergent-solubilized
oxidases, detergent alkyl chains may substitute to lipid acyl chains (Qin et al. 2006, 2007)
(Fig. 1.22) (see also Tsukihara et al. 1996; Shinzawa-Itoh et al. 2007, for cytochrome c oxidase, and
Palsdottir and Hunte 2004; Wenz et al. 2009; Vinothkumar 2011, for similar observations with the
cytochrome bc 1 complex and bacterial GlpG). Examples of the same region on the protein surface
being occupied by a hydrophobic chain in parallel MD simulations carried out either in a lipid or in a
detergent environment have also been reported (see e.g. Rouse and Sansom 2015).
What these observations point to is that lipids should not be regarded as a featureless
two-dimensional solvent, whose bulk physical properties only should be taken into consideration
when considering their effects on integral MPs. Many of them bind at defined positions at the TM
Fig. 1.21 Lipids in the Photosystem I reaction center supertrimer from the thermophilic cyanobacterium
Synechococcus elongatus. (A) Overall view of the supertrimer in projection on the plane of the membrane.
Dashed lines mark the approximate limits of a supermonomer, a black triangle the threefold symmetry
axis. (B) Overall view of a supermonomer, showing only the cofactors and lipids (the side chains of the
antenna chlorophyll a molecules have been omitted). The four lipids are in turquoise: PG phosphatidylglycerol, MGDG monogalactosyl diglyceride. (C) Details of the liganding of the magnesium atom of a
chlorophyll a molecule by the phosphate group of PG III (Adapted from Jordan et al. 2001. # 2001
Macmillan Publishers Limited, Nature. All rights reserved).
30
1 Membrane Proteins and Their Natural Environment