Polyglycines

Examine the structure of the short strand of Nylon 6 in which all amide bonds are Z. What is the monomer unit How many monomers are in the strand Note Each end of the polymer strand has been capped by one or more atoms. Do not count these caps as monomers. Compare the strand to that of a simple polypeptide, for example, polyglycine (see also Chapter 16, Problem 9), and point out any obvious similarities. Pay particular attention to hydrogen bonds. 

Eight exons of the AR gene encode a protein of around 917 aa depending on two polymorphic regions of polyglutamines (CAG) and polyglycines (GGN) in the N-terminal activation domain. Two isoforms are detected in tissues the predominant (80%) 110 kD (B isoform) and 87 kD (A isoform). It is not clear whether the two isoforms also serve different functions. 

Papadopoulos, P. etal. Nanodomain-induced chain folding poly(gamma-benzyl-L-glutamate)-b-polyglycine diblock copolymers. Biomacromolecules, 6, 2352, 2005. 

Kertesz, M., J. Koller, and A. Azman. 1980. On the Electronic Structure of Periodic Polyglycine. Int. J. Quantum Chem. Quantum Biol. Symp. 7, 177-179. 

Otto, P., and A. Sutjianto. 1991. Electron Correlation Effects on the Energy Band Structure of Polyglycine, J. Mol. Struct. (Theochem) 231, 277-282. 

In this connection, it is interesting to note that experimental evidence, including UV, IR and ORD spectroscopy, indicates that the fully extended form of oligoglycine and derivatives of polyglycine is more stable than the a-helix222, 223. In the crystalline state, polyglycine exists in two forms one of which is fully extended and the other nearly extended224 22s. ... 

As defined above, peptoids are peptides in which the side chains are transposed from the backbone C -atom to the amide N-atom. In other words, peptoids are peptides composed of N-monosubstituted glycine units, i. e., N-substituted polyglycine chains. These structural changes have a number of consequences for properties of peptoids relative to peptides [185] [229] ... 

The bulk of all carbohydrates in nature exists in the form of polysaccharides. These are very large molecules formed by linking together long chains of monosaccharide units. These chains may be linear, like polypeptides or polynucleotides, or branched. They may contain a single type of monosaccharide unit, similar to polyglycine or polyA for example, or two or more types of monosaccharide, like nucleic acids (four types of nucleotides) or proteins (20 types of amino acids). However, polysaccharides that contain more than two types of monosaccharide are rare in nature. 

From such a background, some kinds of polypeptide blend samples have been studied by solid state NMR.27,72 74 Especially, detailed information for four kinds of blend samples such as poly(L-alanine) (PLA)/poly(L-valine) (PLV), PLA/poly(L-isoleucine) (PLIL), poly(D-alanine) (PDA)/PLV and polyglycine (PG)/PLV blends, have been reported. Here, let us describe some reasons why PLA/PLV, PDA/PLV, PLA/PLIL and PG/PLV blends are interesting systems. PLA and PDA in the solid-state can take the a-helix and (3-sheet forms due to intra- and intermolecular HBs, respectively. PG in the solid-state can take the 3j-helix (PG-II) and (3-sheet (PG-I) forms due to intra- and intermolecular HBs, respectively. However, PLIL and PLV in the solid state can predominantly take the (3-sheet form as the stable conformation. For this reason, it is interesting to know whether an isolated a-helix or 3i-helix form polypeptide surrounded by a major polypeptide in the (3-sheet form can take the helical conformation, or not, due to the balance between intramolecular and intermolecular hydrogen bonds. In addition, we would like to know whether a polypeptide in the (3-sheet form surrounded by a major polypeptide in the a-helix or 3 -helix form can take the (3-sheet form. 

Romiplostim (AMG 531) is a member of new class of therapeutics called "peptibodies," which are peptides with key biologic activities covalently linked to antibody fragments that serve to extend the peptide s half-life. Romiplostim contains two disulfide-bonded human Fc fragments, each covalently attached through a polyglycine sequence to a peptide... 

II Open systems in two dimensions in which chains are linked to usually six other chains forming a two-dimensional hydrogen-bonded framework. The only known example of this type is fi polyglycine. 

The Ufson-Roig matrix theory of the helix-coil transition In polyglycine is extended to situations where side-chain interactions (hydrophobic bonds) are present both In the helix and in the random coil. It is shown that the conditional probabilities of the occurrence of any number and size of hydrophobic pockets In the random coil can be adequately described by a 2x2 matrix. This is combined with the Ufson-Roig 3x3 matrix to produce a 4 x 4 matrix which represents all possible combinations of any amount and size sequence of a-helix with random coil containing all possible types of hydrophobic pockets In molecules of any given chain length. The total set of rules is 11) a state h preceded and followed by states h contributes a factor wo to the partition function 12) a state h preceded and followed by states c contributes a factor v to the partition function (3) a state h preceded or followed by one state c contributes a factor v to the partition function 14) a state c contributes a factor u to the partition function IS) a state d preceded by a state other than d contributes a factor s to the partition function 16) a state d preceded by a state d contributes a factor r to the partition function. 

N 042 "Molecular Theory of the Helix-Coil Transition in Polylamino acids). III. Evaluation and Analysis of s and [Pg.431]

RIS theory, in the form appropriate for branched molecules, is used to calculate the mean-square unperturbed radius of gyration, < s2>0, for cross-linked polyglycine, poly(L-alanine),poly(L-proline),poly(i-alanyl-D-alanine),poly(i.-prolyl-L-pro lylglycine),poly(L-prolyl-i.-alanylglycine ,poly(glycyl-L-alanyl-L-pro line), andpoly(L-aianyl-L-alanylgIycine).Thecentral amino acid residue in each polypeptide chain is replaced by the L-cysteinyl residue involved in cross-link formation. Each cross-linked molecule is considered to contain two trifunctional branch points, the a-carbon atoms of the two... 

Pleated sheets. While a fully extended polyglycine chain is possible, the side chains of other amino... 

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