Fig. 1.18 Bound lipid molecules at the surface of aquaporin AQP0. In two-dimensional protein/lipid
crystals, the surface of AQP0 is covered by a nearly continuous bilayer of well-defined lipid molecules,
whose structure is distorted to match the rough surface of the protein. The lipids are shown in space-filling
representation; the surface of the protein is colored according to atom charge, ranging from red for
negative to blue for positive (Figure from Lee 2011a, b, # 2011 Elsevier Ltd. All rights reserved. Original
data from Gonen et al. 2005, coordinates from PDB file 2B60. See also Hite et al. 2008).
Fig. 1.19 Amphipathic molecules other than phospholipids can bind in clefts between transmembrane
α-helices. Left, two cholesterol molecules bound to the transmembrane surface of the β 2 -adrenergic
receptor are shown in space-filling representation, circled in yellow. Right, an expanded view of the
binding site, in a cleft on the surface of the protein (Figure from Lee 2011a, b, # 2011 Elsevier Ltd. All
rights reserved. Original data from Hanson et al. 2008, coordinates from PDB file 3D4S).
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1 Membrane Proteins and Their Natural Environment