Model amphipathic peptide

A common characteristic of CPPs is that they contain a minimal motif of less than 20 amino acids rich in basic residues. There are two subclasses of CPPs the first class consists of amphipathic helical peptides, where lysine is the predominant supplier of the positive charge, for example model amphipathic peptide (MAP) and transportan, whereas the second group, which includes TAT and penetratin, is rich in arginine residues (48-60,86). 

Comparison of four CPPs— penetratin (5), Tat (6), transportan (12), and model amphipathic peptide (MAP) (13)— revealed that a model peptide cargo was most efficiently delivered into Bowes melanoma cells by MAP and transportan peptides. As judged by energy transfer experiments (31), the intracellular concentration of a cargo peptide delivered into cells by penetratin or Tat remained three- to fourfold lower compared with transportan- and MAP-mediated delivery. On the other hand, transportan and MAP were more noxious to cells and increased the plasma membrane permeability at lower concentrations. Import of penetratin sequences by the melanoma-derived SKMel-37 cells was in turn three- to fourfold more efficient than uptake of MTS-sequences as measured by fluorescence correlation spectroscopy in living cells and by FACS analysis (32). 

The so-called model amphipathic peptide (MAP) was originally designed to form an amphipathic a-helix and was later found to be cell-penetrating [90, 91]. Four leucines were selectively replaced with CF3-Phg, and 19F NMR on these different analogues showed the same kind of concentration-dependent realignment of the helix from S- to T-state as was observed for the other helical peptides discussed above. Additionally, we could... 

CPP are mainly divided into two types (1) amphipathic helical peptides such as trans-portin and model amphipathic peptide having lysine as a main contributor to the positive charge, and (2) arginine-rich peptides such as transactivating transcriptional activator (TAT) and homeodomain of antennapedia (Antp) [54]. The HIV-1 TAT peptide is composed of six arginine units and two lysine units in the sequence and is known to show high permeability to the cell membrane, which has been combined with several materials for effective delivery into the cytoplasm [58,59]. Mao et al. prepared a fluorescein isothiocyanate (FlTC)-SiNPs-TAT peptide (around 200 nm), and estimated their ability for... 

This approach was later extended to off-lattice models and a more detailed description of the transfer energy of the different amino acid residues [77]. Magainin, melit-tin, and several other amphipathic peptides were simulated. In these simulations, differences in the interaction of the peptides with the lipid phase were observed. For example, magainin only showed adsorption onto the lipid and no crossing of the lipid occurred, whereas melittin crossed the lipid and formed a stable transmembrane helix. These results are in full agreement with later studies reported by other research groups presented below, involving more elaborate simulation protocols and representations of the peptides and the lipid. These examples show the potential of computer simulations even when some simplifications have to be made to make the system computationally tractable. 

Conjugation of a DNA/PEI or DNA/PEI-PEG polyplex to targeting moieties such as antibodies to surface antigens like HER2 for breast cancer and OA3 for ovarian cancer has been shown to increase the transfection efficiency in vitro (50,51). PEI can also be lined with amphipathic peptides in order to facilitate cell entry in vivo. PEI coated with the KALA (WEAK-LAKALAKALAKHLAKALAKALKACEA) peptide has been shown to have higher transfection efficiency in a murine model than plain PEI or a commercial liposome (52). 

Figure 18.1 Models for different modes of peptide-lipid interaction of membrane-active peptides. The peptide remains unstructured in solution and acquires an amphipathic structure in the presence of a membrane. The hydrophobic face of the amphipathic peptide binds to the membrane, as represented by the grayscale. At low concentration, the peptide lies on the surface. At higher peptide concentrations the membrane becomes disrupted, either by the formation of transmembrane pores or by destabilization via the "carpet mechanism." In the "barrel-stave pore" the pore consists of peptides alone, whereas in the "toroidal wormhole pore" negatively charged lipids also line the pore, counteracting the electrostatic repulsion between the positively charged peptides. The peptide may also act as a detergent and break up the membrane to form small aggregates. Peptides can also induce inverted micelle structures in the membrane.

Barrel-stave model Model for pore-forming amphipathic peptides in which the polar face forms a hydrophilic pore. 

The interaction between a synthetic amphipathic peptide and model membranes. 

An amphipathic helix is defined as a helix in which the distribution of amino acid residues forms opposing polar and nonpolar faces. It is an important structural unit included in proteins and peptides and is responsible for interaction with biological membranes to elicit their biological functions such as membrane fusion. Influenza virus hemagglutinin [1], fertilin [1], and meltrin-a [2] contain amphipathic fusion peptides, which are likely to adopt a helical conformation during the fusion reaction. To clarify the role of amphipathic peptides in membrane fusion reactions, we synthesized five types of amphipathic model peptides and examined their helix formation, membrane binding and membrane fusion activities. 

The amphipathic peptides used in the present study were model peptides with 51, 47, and 22 amino acid residues (KL-51 [3], KL-47, and KL-22, respectively), all of which consist of tandem repeats of a KKLL sequence, a model peptide of leucine zipper with 26 amino acid residues (LZ-26), and a cationic peptide as an analog of the influenza hemagglutinin fusion peptide with 20 amino acid residues (HK-20) [4]. 

Melittin is an amphipathic peptide which has received much attention as a model peptide for peptide-membrane interactions. It is however not suited as a transfection agent due to its cytolytic and toxicologic effects. Retro-inverso-melittin, when covalently linked to the lipid l,2-dioleoyl-s -gZycero-3-phosphoethanolamine (riDOM), eliminates these shortcomings. RiDOM forms cationic nanoparticles with a diameter of 13 nm which are well soluble in water and bind with high affinity to DNA and lipid membranes. RiDOM-induced membrane leakiness is however much reduced compared to that of authentic melittin. The P NMR spectrum of the nanoparticle is however transformed into a typical bilayer spectrum. ... 

Oehlke and coworkers have described the cellular uptake properties of a simple a-hehcal amphipathic model peptide sequence (Lys-Leu-Ala-Leu-Lys-Leu-Ala-Leu-Lys-Ala-Leu-Lys-Ala-Ala-Leu-Lys-Leu-Ala) in the context of a drug delivery vehicle [72]. On the basis of the data presented, it was proposed that non-endocytosis mechanism(s) were involved in the uptake into mammalian cells. The similarity between our b2 aPNA-sequence to that of this amphipathic model peptide makes it tempting to suggest that a similar uptake mechanism is involved in the cellular uptake of aPNAs. Further experimentation is necessary to test this hypothesis. 

ApoA-II has served as a model protein for studies on the lipid-binding properties of peptides. Each 77-amino-acid peptide chain has three segments which have been proposed as amphipathic helices. There is evidence, summarized by Sparrow and Gotto (S52), that suggests that these segments form helices in the presence of phospholipid (with or without cholesterol), that is, that the proposed a-helices are in fact the lipid-binding segments. 

Besides Ap, other amphipathic model peptides are also studied using IRRAS. The linear sequence KLAL (KLALKLALKALKAALKLA-NH2) is a model compound to form amphipathic helices, which is able to bind to membranes and to increase the membrane permeability in a structure and target-dependent manner [71,72], Kerth et al. first studied the secondary structure of... 

Given the limitations of the above systems, it is apparent that the optimal peptide model of a p-sheet (and a p-turn) should be as analagous to the monomeric helix models as possible. In particular, the ideal p-sheet model should be small (< 20 residues), monomeric, water-soluble, pure (composed of only p-sheets and p-turns), amphipathic (to investigate sidedness), reversibly denaturable, composed of only natural amino acids, easily synthesized and easily characterized by standard spectroscopic techniques. We believe that we have developed such a peptide model. It is based on the naturally occurring cyclic peptide gramicidin S, an antibiotic produced by the bacterium bacillus brevis (12). The schematic structure of gramicidin S as determined by X-ray and NMR studies (13, 14) is shown in Figure 1. 

The amphipathic a helix, defined as an a helix with opposing polar and nonpolar faces oriented along its long axis, is a common secondary structural motif in biologically active peptides and proteins. The discovery of this structural motif was made by studying space-filling models of... 

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