Amino acid sequence specific polymers

Several authors have compared imprinted polymers to biological receptors and even the term plastic antibodies has been coined to describe these remarkable materials. To a large extent, this comparison rests on a spectacular work of Mosbach and co-workers [24], who showed that theophylline- and diazepam-imprinted polymers displayed a specificity rather similar to that of polyclonal antibodies in binding studies with the template and its close structural analogues. However, it is the recognition of nucleotide or oligopeptide sequences which is 

The polymer was prepared using conventional procedures and an initial analysis showed that it was capable of binding the tripeptide (11) in aqueous acetonitrile at 

Overall these data clearly demonstrate that polymers prepared by the combina- 

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Identity Sequence-specific polymers of amino acids Sequence-specific polymers of N-substituted glycines... 

Fibrous proteins are long-chain polymers that are used as structural materials. Most contain specific repetitive amino acid sequences and fall into one of three groups coiled-coil a helices as in keratin and myosin triple helices as in collagen and p sheets as in silk and amyloid fibrils. 

Protein polymers based on Lys-25 were prepared by recombinant DNA (rDNA) technology and bacterial protein expression. The main advantage of this approach is the ability to directly produce high molecular weight polypeptides of exact amino acid sequence with high fidelity as required for this investigation. In contrast to conventional polymer synthesis, protein biosynthesis proceeds with near-absolute control of macromolecular architecture, i.e., size, composition, sequence, topology, and stereochemistry. Biosynthetic polyfa-amino acids) can be considered as model uniform polymers and may possess unique structures and, hence, materials properties, as a consequence of their sequence specificity [11]. Protein biosynthesis affords an opportunity to completely specify the primary structure of the polypeptide repeat and analyze the effect of sequence and structural uniformity on the properties of the protein network. 

The first basic tenet of protein-structure prediction is that the amino acid sequence, the primary structure, contains all of the information required for the correct folding of the polymer chain. This is a first approximation which clearly ignores the role of environment on the induction of structure or the action of chaperone proteins which assist the in vivo folding process. The wide variety of structural motifs that have been observed for proteins is derived from only twenty different monomers (amino acids), many of which are structurally quite similar (i.e., isoleucine and leucine vary only in branching of the butyl side chain). However, there are many cases in which the substitution of amino acids with structurally similar residues (so-called conservative substitution) will lead to a protein that will not properly fold. Studies involving deletion of even small portions of the termini of the protein sequence provide similar results. On the other hand there are proteins related through evolution with as little as 20% sequence identity which adopt similar three-dimensional structures. Therefore the information encoded in the primary sequence is specific for one protein fold, however, there are numerous other sequences, only remotely related at first glance, which will produce the same fold. 

We have already discussed primary structure in terms of the general character of amino acids and some specific examples of amino acid sequences in certain proteins will be discussed later. Our attention now is focused on secondary structure, or conformation as we called it when we discussed synthetic polymers. There are a number of factors that afreet the conformation of a polypeptide chain and a lot can be learned initially by just focusing on two of these steric restrictions on bond rotations and the strong driving force for amide groups to hydrogen bond to one another. 

Amino acid polymerization requires elimination of a water molecule as the carboxyl group of one amino acid reacts with the amino group of another amino acid to form a covalent amide bond. The repetition of this process with many amino acids yields a polymer, known as a polypeptide. The amide bonds linking amino acids to each other are known as peptide bonds. Each amino acid unit within the polypeptide is referred to as a residue. The sequence of amino acids in a protein is dictated by the sequence of nucleotides in a segment of the DNA in the chromosomes and the uniqueness of each living organism is due to its endowment of specific proteins. 

Specific amino acid sequences promote cell adhesion. The most commonly used sequence is the RGDs from adhesion proteins. Photo-cross-linking RGD peptides to chitosan improved the adhesion of human endothelial cells, compared to unmodified chitosan scaffolds [109]. In another approach, the -COOH group of amino acids such as lysine, arginine, aspartate, and phenylalanine reacts to the -NH group of chitosan. These functionalized chitosan polymers were entrapped onto the surface of PLA to improve cellular responses [110]. 

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