potential-driven desorption of the lipid bilayer is responsible for reorientations of
recoverin. The protein adopts a more perpendicular with respect to the bilayer
surface orientation, as illustrated in Fig. 3.23b. The interaction of anchor proteins
with cell membranes depends in the membrane potential. Described above results
[44, 45] show that dispersion forces affecting the packing of the hydrocarbon chains
as well as charge-charge and charge-dipole interactions contribute to the total
interaction energy of the anchor protein with the lipid membrane. This interaction
affects the conformation and orientation of the protein interacting with the lipid
bilayer.
Some proteins interact with lipid membranes via binding to a specific polar
residue (e.g. saccharide, phosphate residues) in a lipid molecule. Binding of a protein
to saccharide moieties is known as the protein-carbohydrate interaction
[110, 111]. Experimental studies of the protein-carbohydrate interactions are challenging due to a large diversity of flexible in conformation of glycolipids present on
the membrane surface. The strength of this interaction includes strong and irreversible (e.g. toxin proteins) [112, 113] as well as weak and reversible
(e.g. immunoglobulin-like lectins) binding [114]. In situ PM IRRAS was used to
study the membrane structure experiencing the carbohydrate-protein interactions
with a myelin-associated glycoprotein, siglec-4 (weak binding) [39] and cholera
toxin B (strong binding) [42] protein.
Immunoglobulin-like lectins (siglecs) bind to the sialic acid residue in glycolipids
present on the extracellular leaflet of the cell membrane [115, 116]. Siglec proteins
are an important part of the immune system, because they bind reversibly to the
glycolipids blocking the binding sides of some toxin proteins (e.g. cholera toxin). In
situ PM IRRAS was used to study the protein-carbohydrate interactions [39]. To
differentiate the spectroscopic answer of both leaflets of the bilayer perdeuterated
phospholipids were used. Figure 3.24 shows the PM IRRA spectra in the CH
stretching modes region of the outer [DMPC:cholesterol:GD 1a (5:3:2) and inner
DMPC:cholesterol (7:3)] leaflets of the model membrane in the absence and
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
30
35
40
45
50
55
60
65
70
f
o
l
t
i
t
e
g
a
r
e
A
g
e
d
/
s
e
c
i
l
e
h
-
Transmembrane potential / V
Fig. 3.22 Average tilt of
long axes of α-helices in
recoverin (black rhombuses)
and n-recoverin (grey
circles) interacting with the
DMPC:cholesterol bilayer
on the Au electrode surface
versus transmembrane
potential plots in negative
going (full symbols) and
positive going (open
symbols) potential scans.
Figure taken from [45] and
modified
82
3 In Situ PM IRRAS Studies of Redox-Inactive Molecular Films Adsorbed on. . .
recoverin. The protein adopts a more perpendicular with respect to the bilayer
surface orientation, as illustrated in Fig. 3.23b. The interaction of anchor proteins
with cell membranes depends in the membrane potential. Described above results
[44, 45] show that dispersion forces affecting the packing of the hydrocarbon chains
as well as charge-charge and charge-dipole interactions contribute to the total
interaction energy of the anchor protein with the lipid membrane. This interaction
affects the conformation and orientation of the protein interacting with the lipid
bilayer.
Some proteins interact with lipid membranes via binding to a specific polar
residue (e.g. saccharide, phosphate residues) in a lipid molecule. Binding of a protein
to saccharide moieties is known as the protein-carbohydrate interaction
[110, 111]. Experimental studies of the protein-carbohydrate interactions are challenging due to a large diversity of flexible in conformation of glycolipids present on
the membrane surface. The strength of this interaction includes strong and irreversible (e.g. toxin proteins) [112, 113] as well as weak and reversible
(e.g. immunoglobulin-like lectins) binding [114]. In situ PM IRRAS was used to
study the membrane structure experiencing the carbohydrate-protein interactions
with a myelin-associated glycoprotein, siglec-4 (weak binding) [39] and cholera
toxin B (strong binding) [42] protein.
Immunoglobulin-like lectins (siglecs) bind to the sialic acid residue in glycolipids
present on the extracellular leaflet of the cell membrane [115, 116]. Siglec proteins
are an important part of the immune system, because they bind reversibly to the
glycolipids blocking the binding sides of some toxin proteins (e.g. cholera toxin). In
situ PM IRRAS was used to study the protein-carbohydrate interactions [39]. To
differentiate the spectroscopic answer of both leaflets of the bilayer perdeuterated
phospholipids were used. Figure 3.24 shows the PM IRRA spectra in the CH
stretching modes region of the outer [DMPC:cholesterol:GD 1a (5:3:2) and inner
DMPC:cholesterol (7:3)] leaflets of the model membrane in the absence and
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
30
35
40
45
50
55
60
65
70
f
o
l
t
i
t
e
g
a
r
e
A
g
e
d
/
s
e
c
i
l
e
h
-
Transmembrane potential / V
Fig. 3.22 Average tilt of
long axes of α-helices in
recoverin (black rhombuses)
and n-recoverin (grey
circles) interacting with the
DMPC:cholesterol bilayer
on the Au electrode surface
versus transmembrane
potential plots in negative
going (full symbols) and
positive going (open
symbols) potential scans.
Figure taken from [45] and
modified
82
3 In Situ PM IRRAS Studies of Redox-Inactive Molecular Films Adsorbed on. . .