Secondary structures, amphiphilic,

C. Design of Peptides That Form Amphiphilic Secondary Structures. 80... 

Fig. 3.17. Amphiphilic secondary structures. By specifying the locations of polar (light gray) and nonpolar (dark gray) residues through simple binary patterns, amphiphilic helical or pi-sheet structures can be designed [154].

The Gellman laboratories later reported the chemical synthesis of a 17-mer based on the 12-helix forming trani-2-aminocyclopentanoic acids [64]. Charged amine fimctionalities in combination with neutral monomer units were incorporated into the oligomer to provide an amphiphilic secondary structure (Fig. 35). When tested for bactericidal and bacteriostatic activity against a vancomycin-resistant bacterial strain, this material exhibited activity similar to that of a known 23-mer... 

Sequence analysis of P.h. reveals that many are capable of adopting stable amphiphilic secondary structures at membrane/aqueous interfaces. That such structures are important to the action of the P.h. is indicated by studies with synthetic analogs with similar or dissimilar amphiphilicity but otherwise different primary structures from the natural P.h. [E. T. Kaiser F. J. Krady Science 223 (1984) 249-255]... 

There are many further issues that can be addressed by the model of the kind described here. Clearly, the HA model is amenable to a number of generalizations that allow one to study more sophisticated features of amphiphilic copolymers, including, for instance, backbone stiffness, orientational degrees of freedom, or additional structural constraints such as the saturation of monomer-monomer interactions [98], which are crucial, e.g., for the folding of RNA. Also, it is easy to introduce dipole moments for side H - P bonds and specific directional interactions (like hydrogen bonds) for some of the chain units. These additional factors can result in the formation of intramolecular secondary structures and lead to an increase in the stability of globules formed by such polymers. 

Methodologies to assess interface properties of amphiphiles are surface tension measurements (Phan et al. 2006 Golding and Sein 2004 Miller et al. 2004), ellip-sometry (Dickinson 2003a Murray 2002) and Brewster angle microscopy (Grigoriev et al. 2006 Rodrguez Patino et al. 2001). Both and P NMR have been applied in order to study the conformation and dynamics of P-casein at the oil-water interface of emulsions (ter Beek et al. 1996). Their NMR results showed that the protein at the interface has mobile regions with httle secondary structure in which the motions are rather slow. 

A salient feature of all known pores is their irreversible anchorage in the lipid bilayer (Bhakdi and Tranum-Jensen, 1987). Hence, membrane-bound PFTs must be amphiphilic, possessing a lipid binding surface and a hydrophilic face that lines the aqueous channel. The pore-forming domains themselves are unlikely to harbor extended stretches of hydrophobic amino acid residues. Rather, they would be expected to possess amphipathic secondary structure. Rules to identify or predict pore-forming sequences do not exist, and even the solution of the structure of a water-soluble protomer form will not permit conclusions to be drawn on the structure of the pore. This situation is given in the case of aerolysin (Parker et al., 1996). 

This review covers the literature on the aggregation of (homo)polypeptide hybrid copolymers and copolypeptides in dilute solution, which was published up to June 2005 a recent review on amphiphiles consisting of peptide sequences is given elsewhere in [12]. It was a particular concern to give a comprehensive overview on secondary structure effects in the self-assembly of these copolymers. Briefly presented are also structures in concentrated solutions (lyotropic phases) and in heterophase systems (see also [14]). 

A new polymeric amphiphile based on cationic poly(L-lysine), which was partially modified with hydrophobic palmitoyl chains and hydrophilic neutral methoxy-poly(ethylene glycol) (Fig. 7e), was introduced by Uchegbu et al. [38,39], In water in the presence of cholesterol, these copolymers assembled into vesicles with diameters ranging from 200 to 600 nm (DLS, freeze-fracture TEM), depending on the chemical composition of the copolymer and the length of the polypeptide backbone. More detailed information about the secondary structure of chains and the structure of vesicle membranes were not given. 

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