242
M. Melicherčík et al.
In some cases the tilt was replaced by superhelical double-twisted structure. The
rest of helices were bend or produced kink in addition to the tilt. The lipid structural
state around the peptide has been also analyzed.
8.1 Introduction
Lipid–protein interactions are of fundamental importance for understanding both
the structural integrity and the functions of biological membranes [1, 2]. In particular, the chemical composition and physical properties of the lipid bilayer membranes
(BLMs) can markedly influence the activity, thermal stability, and the location and
disposition of a large number of integral membrane proteins in both model and
biological membranes [2]. For these reasons, many studies of the interactions of
membrane proteins with their host BLM have been carried out, in both biological and reconstituted model systems, employing a wide range of different physical
techniques [3–6]. To overcome the problem of the complicated structure of integral
proteins and the problems with their isolation and purification, a number of workers
have designed and synthesized peptide models of specific regions of natural membrane proteins and have studied their interactions with model lipid membranes of
defined composition (see [7, 8]). In particular, the study of the mechanisms of the
interactions of peptides with BLM has also very important practical significance for
understanding of the mechanism of interaction of e.g. neuropeptides [9] or antimicrobial peptides [10] with membranes. The cell-penetrating-peptides can also transport other macromolecules inside the cell and thus are perspective in drug delivery.
The synthetic peptide acetyl-K 2 -G-L 24 -K 2 -A-amide (P 24 ) and its structural analogs, e.g. acetyl-K 2 -L 24 -K 2 -amide (L 24 ), have been successfully utilized as a model
of the hydrophobic transmembrane α-helical segments of integral proteins [8, 11].
These peptides contain a long sequence of hydrophobic leucine residues capped at
both the N- and C-termini with two positively charged lysine residues. The central polyleucine region of these peptides was designed to form a maximally stable
α-helix which will partition strongly into the hydrophobic environment of the lipid
bilayer core, while the dilysine caps were designed to anchor the ends of these
peptides to the polar surface of the BLM and to inhibit the lateral aggregation of
these peptides. In fact, circular dichroism (CD) [11] and Fourier transform infrared
spectroscopy FTIR [12] spectroscopic studies of P 24 have shown that it adopts a
very stable α-helical conformation both in solution and in lipid bilayers. X-ray diffraction [13], fluorescence quenching [14] and FTIR [12] and deuterium nuclear
magnetic resonance (
2
H-NMR) [15] spectroscopic studies have confirmed that P 24
and its analogs assume a transbilayer orientation with the N- and C-termini exposed
to the aqueous environment and the hydrophobic polyleucine core embedded in hydrocarbon core of the BLM when reconstituted with various phosphatidylcholines
(PCs) [16].
2
H-NMR [17] and electron spin resonance (ESR) [18] spectroscopic
studies have shown that the rotational diffusion of P 24 about its long axis perpendicular to the membrane plane is rapid in the liquid-crystalline state of the bilayer.
M. Melicherčík et al.
In some cases the tilt was replaced by superhelical double-twisted structure. The
rest of helices were bend or produced kink in addition to the tilt. The lipid structural
state around the peptide has been also analyzed.
8.1 Introduction
Lipid–protein interactions are of fundamental importance for understanding both
the structural integrity and the functions of biological membranes [1, 2]. In particular, the chemical composition and physical properties of the lipid bilayer membranes
(BLMs) can markedly influence the activity, thermal stability, and the location and
disposition of a large number of integral membrane proteins in both model and
biological membranes [2]. For these reasons, many studies of the interactions of
membrane proteins with their host BLM have been carried out, in both biological and reconstituted model systems, employing a wide range of different physical
techniques [3–6]. To overcome the problem of the complicated structure of integral
proteins and the problems with their isolation and purification, a number of workers
have designed and synthesized peptide models of specific regions of natural membrane proteins and have studied their interactions with model lipid membranes of
defined composition (see [7, 8]). In particular, the study of the mechanisms of the
interactions of peptides with BLM has also very important practical significance for
understanding of the mechanism of interaction of e.g. neuropeptides [9] or antimicrobial peptides [10] with membranes. The cell-penetrating-peptides can also transport other macromolecules inside the cell and thus are perspective in drug delivery.
The synthetic peptide acetyl-K 2 -G-L 24 -K 2 -A-amide (P 24 ) and its structural analogs, e.g. acetyl-K 2 -L 24 -K 2 -amide (L 24 ), have been successfully utilized as a model
of the hydrophobic transmembrane α-helical segments of integral proteins [8, 11].
These peptides contain a long sequence of hydrophobic leucine residues capped at
both the N- and C-termini with two positively charged lysine residues. The central polyleucine region of these peptides was designed to form a maximally stable
α-helix which will partition strongly into the hydrophobic environment of the lipid
bilayer core, while the dilysine caps were designed to anchor the ends of these
peptides to the polar surface of the BLM and to inhibit the lateral aggregation of
these peptides. In fact, circular dichroism (CD) [11] and Fourier transform infrared
spectroscopy FTIR [12] spectroscopic studies of P 24 have shown that it adopts a
very stable α-helical conformation both in solution and in lipid bilayers. X-ray diffraction [13], fluorescence quenching [14] and FTIR [12] and deuterium nuclear
magnetic resonance (
2
H-NMR) [15] spectroscopic studies have confirmed that P 24
and its analogs assume a transbilayer orientation with the N- and C-termini exposed
to the aqueous environment and the hydrophobic polyleucine core embedded in hydrocarbon core of the BLM when reconstituted with various phosphatidylcholines
(PCs) [16].
2
H-NMR [17] and electron spin resonance (ESR) [18] spectroscopic
studies have shown that the rotational diffusion of P 24 about its long axis perpendicular to the membrane plane is rapid in the liquid-crystalline state of the bilayer.