Simple sequence repeat characteristics

In the proceeding sections, emphasis has been placed on pH-responsive homopolymers whose conformational behavior is dictated by the hydrophobic to hydrophilic balance within the system. The switch in conformation is marked by a change in macroscopic properties, such as solution viscosity, over a narrow and characteristic pH range specific to that polymer which is important from a technological viewpoint. Manipulation of the switch to any desired pH has attracted much interest in the literature because this could lead to many more potential applications for the modified poly electrolyte. Synthetic strategies adopted to achieve this end have included simple copolymerization of an ionizable repeat unit with a hydrophobic monomer [20,27—43,1291 to form statistical copolymers and formation of block copolymers [71,158-180]. (A block copolymer consists of sequences of monomers A and B such as -(A) -(B)m or -(A) -(B)m-(A) , where n and m represent the number of repeat units.)... 

The term polymer (poZy-many, and monomer-low molar mass unit) reflects the simplicity of the high molecular weight macromolecular structure. Natural polymers, although they may have complex sequences of repeat imits, can exhibit physical properties that obey the same physical laws as their equivalent synthetic polymers. The increased use of polymers in everyday life has come with the discovery of simple synthetic routes to the raw materials and the ability to tailor their physical properties to particular applications. Despite the wide range of methods available for their synthesis, the physical characteristics of many polymers can be predicted by recognizing certain generic features in their structure. 

Lowik et demonstrated that the secondary structure of certain peptide sequences conjugated to single Ci8 alkyl chains at both the N- and C-termini could be induced upon incorporation into a liposome membrane. A sequence derived from the circumsporozoite (CS) protein of the malaria parasite Plasmodium falciparum was chosen, as within the natural protein the Asn-Pro-Asn-Ala repeat is known to adopt a j6-tum. Both the unmodified peptide in solution and the analogous peptide with only one alkyl chain showed random coil folding characteristics. However, when the double alkylated peptide was inserted into l,2-dimyristoyl-OT-glycero-3-phosphoethanol-amine (DSPC) liposomes the peptide folded into a P-hairpin. This simple approach is a convenient way for stabilizing a variety of peptides into their preferred secondary structure and might be employed in the presentation of multiple (hairpin) epitopes. 

---