In the presence of perfluorinated organic compounds in the outer leaflet of the
DMPC bilayer the average tilt angle of the hydrocarbon chains in lipid molecules
decreases compared to the pure DMPC bilayer (solid circles, Fig. 3.14). In the pure
DMPC bilayer adsorbed directly on the Au surface the average tilt of the hydrocarbon chains in the outer leaflet is equal to 35
versus surface normal [31]. In the
presence of PFOS in the outer leaflet of the DMPC bilayer the chain tilt is equal to
24
while in presence of PFOA to 30
(open circles, Fig. 3.14) [40]. Incorporation of
PFOS and PFOA has a condensing effect on the lipid bilayer. Results of this work
show that in situ PM IRRAS is applicable not only to discuss potential-driven
changes in models of cell membranes but it is an excellent tool to monitor the
interaction of lipid bilayers with other molecules.
3.3.3 Determination of Potential-Driven Structural Changes
in Models of Cell Membranes Interacting with Peptides
and Proteins: In Situ PM IRRAS
The fluid lipid matrix of biological membranes interacts with proteins. Proteins
interact with the lipid membranes according to different mechanisms [81, 82]:
1. Protein binding to a residue present in the polar head group of a lipid
(e.g. saccharide moiety, carboxylic moiety);
2. Electrostatic interactions between charged groups in a polar head group of lipid
and protein molecules;
3. Anchoring of a hydrophobic protein fragment into a lipid membrane;
4. Insertion of a fragment of a lipid molecule into the protein (e.g. a hydrocarbon
chain);
5. Insertion of a transmembrane or peripheral protein into the lipid part of the
membrane;
6. Aggregation of monomers of transmembrane proteins.
Lipid-protein interactions may affect the membrane capacitance, resistance and
permeability. Changes of the macroscopic membrane properties may affect the
structure and packing of the lipid molecules in the membrane [83, 84]. In situ studies
of the protein structure and its changes induced for example by the interaction with a
cell membrane is a challenging experimental task. Infrared spectroscopy (IRS) is a
very convenient method to study in situ, in the solution phase, the conformation of
proteins. Proteins are long chain heteropolymers composed of 20 L-α amino acids
monomers and connected via peptide bonds. The primary structure of a protein refers
to the sequence of amino acids in the polypeptide chain. Proteins fold into specific
conformations, which are referred to as the secondary and tertiary structure of a
protein. The folding of the polypeptide chain in the protein is driven by hydrogen
bonding, charge-charge interactions, attractive van der Waals forces and hydrophobic packing. Regular local substructures such as α-helices and β-strands or β-sheets
70
3 In Situ PM IRRAS Studies of Redox-Inactive Molecular Films Adsorbed on. . .
DMPC bilayer the average tilt angle of the hydrocarbon chains in lipid molecules
decreases compared to the pure DMPC bilayer (solid circles, Fig. 3.14). In the pure
DMPC bilayer adsorbed directly on the Au surface the average tilt of the hydrocarbon chains in the outer leaflet is equal to 35
versus surface normal [31]. In the
presence of PFOS in the outer leaflet of the DMPC bilayer the chain tilt is equal to
24
while in presence of PFOA to 30
(open circles, Fig. 3.14) [40]. Incorporation of
PFOS and PFOA has a condensing effect on the lipid bilayer. Results of this work
show that in situ PM IRRAS is applicable not only to discuss potential-driven
changes in models of cell membranes but it is an excellent tool to monitor the
interaction of lipid bilayers with other molecules.
3.3.3 Determination of Potential-Driven Structural Changes
in Models of Cell Membranes Interacting with Peptides
and Proteins: In Situ PM IRRAS
The fluid lipid matrix of biological membranes interacts with proteins. Proteins
interact with the lipid membranes according to different mechanisms [81, 82]:
1. Protein binding to a residue present in the polar head group of a lipid
(e.g. saccharide moiety, carboxylic moiety);
2. Electrostatic interactions between charged groups in a polar head group of lipid
and protein molecules;
3. Anchoring of a hydrophobic protein fragment into a lipid membrane;
4. Insertion of a fragment of a lipid molecule into the protein (e.g. a hydrocarbon
chain);
5. Insertion of a transmembrane or peripheral protein into the lipid part of the
membrane;
6. Aggregation of monomers of transmembrane proteins.
Lipid-protein interactions may affect the membrane capacitance, resistance and
permeability. Changes of the macroscopic membrane properties may affect the
structure and packing of the lipid molecules in the membrane [83, 84]. In situ studies
of the protein structure and its changes induced for example by the interaction with a
cell membrane is a challenging experimental task. Infrared spectroscopy (IRS) is a
very convenient method to study in situ, in the solution phase, the conformation of
proteins. Proteins are long chain heteropolymers composed of 20 L-α amino acids
monomers and connected via peptide bonds. The primary structure of a protein refers
to the sequence of amino acids in the polypeptide chain. Proteins fold into specific
conformations, which are referred to as the secondary and tertiary structure of a
protein. The folding of the polypeptide chain in the protein is driven by hydrogen
bonding, charge-charge interactions, attractive van der Waals forces and hydrophobic packing. Regular local substructures such as α-helices and β-strands or β-sheets
70
3 In Situ PM IRRAS Studies of Redox-Inactive Molecular Films Adsorbed on. . .