Homopolypeptide

It is well known that native collagen containes tripeptide sequences, which alone are not capable of building up a triple helix (e.g. Gly-Pro-Leu, Gly-Pro-Ser) when they exist as homopolypeptides. The synthesis of threefold covalently bridged peptide chains opens up the possibility of investigating the folding properties of such weak helix formers, because the bridging reduces the entropy loss during triple-helix formation and thereby increases the thermodynamic stability of the tertiary structure. Therefore, we have... 

It is known that native collagen contains tripeptide sequences which, because of being homopolypeptides, are not able to give rise to triple-helical tertiary structures (e.g. Gly-Pro-Leu, Gly-Pro-Ser). The reason for this and for the above-mentioned low thermostability of the synthetic homopolypeptides is presumably to be found in the fact that in the case of the model peptides with their monotonously repeated tripeptide sequences, special interactions between the side chains of the different amino acid residues as postulated by Ward and Mason are no more possible157). 

The first step of NCA polymerization is usually accomplished by the use of nucleophilic initiators. These initiators can be alkoxides, alcohols, amines, transition metals, and even water [53,54]. In order to synthesize a copolymer diblock, the polymerization of the second block and its connection to the previously formed block are performed in a single process. This is achieved by initiating the polymerization of the second NCA monomer using the first homopolypeptide as a macroinitiator. Precipitation and purification processes follow to isolate the... 

Heparin has been reported to complex with a variety of basic species, including biogenic amines and drugs for reviews, see Refs. 10 and 391. For its possible relevance to the pharmacological properties of heparin and complexed species, mention is made here of complexes with histamine392,393 and anthracycline antibiotics.394 C.d. studies on the interaction of basic homopolypeptides with heparin and other glycosaminogly-cans have shown that heparin is able to induce an ordered, helical conformation in the polypeptide.395 397 Similar, and even more dramatic, effects were observed with mixed basic polypeptides, presumed to represent better models for the biologically relevant interactions with plasma proteins.368... 

Ladik, J., A. Sutjianto, and P. Otto. 1991. Improved Band Structures of Some Homopolypeptides with Aliphatic Side Chains and of the Four Nucleotide Base Stacks Estimation of Their Fundamental Gap. J. Mol. Struct. (Theochem) 228, 271-276. 

The long side chains of a homopolypeptide have remarkable motional freedom about multiple bonds, while the main chain forms the secondary regular conformation such as a-helix, /1-sheet, and turn, which are rigid structures. The macroscopic properties of the rigid a-helical polypeptide, therefore, highly depends on the dynamic structure of the side chains so that a lot of studies on the side chain dynamics of the a-helical polypeptides have been carried out in the solid and solution states.12,14,29 66... 

These transformations arise from the energetical stability caused by intramolecular or intermolecular hydrogen bond (HB) interactions. Thus, by the balance of intramolecular and intermolecular HB interactions in polypeptide blends, it is expected that the strength of intermolecular interaction in the blends is different from those in homopolypeptides then new conformations can be formed by intermolecular HB interactions that do not exist originally in homopolypeptides. There are many studies on intermolecular HB interactions in homopolypeptides and copolypeptides in the solid state, but to the best of our knowledge there is little study on intermolecular HB interactions in polypeptide blends except for our previous studies. 

Table 1. Preferred conformations of homopolypeptides in the solid-state...

On the other hand, the deposition process is also important to prepare blend samples. A mixture of homopolypeptide solutions in which they take a random coiled structure are added into a poor solvent. For polypeptides, water is a poor solvent in general. If the hydration rate is different for each polypeptides, they form their preferred secondary structures by themselves and then do not blend with each other. On the basis of this assumption, in order to make the hydration at the same time, the solution is added to alkaline water. In this review, two kinds of quieting solvents such as water and alkaline water have been used. (Methods 1-4 and Method 5). Method 1 Helical polypeptide and (3-sheet polypeptide are dissolved in DCA and agitated... 

Table 2. Preferred conformations of homopolypeptides used in this review...

C CP/MAS NMR SPECTRAL ANALYSIS AND CONFORMATIONAL CHARACTERIZATION OF HOMOPOLYPEPTIDES AND THEIR .ENDS... 

In order to understand the conformations or conformational changes of homopolypeptides and copolypeptides, solid-state 13C NMR is a very useful... 

Fig. 5. 13 CP/MAS NMR spectra of PLA ( ), PLV ( ) and PLA/PLV blend samples which were prepared by adding their TFA solutions with a 2.0 wt/wt% amount of H2SO4 to alkaline water (Method 5). Homopolypeptides of PLA (a-helix) and PLV (P-sheet) are prepared using same condition as PLA/PLV (80/20, 50/50, 20/80) blend samples. The symbols of starpA) show the new signals that were produced by this blend condition, (a) PLA, (b) PLA/PLV (80/20), (c) PLA/PLV (50/50), (d) PLA/PLV (20/80) and (e) PLV.

The observed 13C CP/MAS NMR spectra of PLA, PLIL and the PLA/PLIL (20/80, 50/50 and 80/20 wt/wt%) blend samples, prepared by adding a TFA solution with a 2.0 wt/wt% amount of H2S04 to alkaline water (Method 5), are shown in Fig. 7. In the spectra, homopolypeptides of PLA (a-helix) and PLIL ((3-sheet) are treated using the same condition as for the mixture of PLA/PLIL blend samples. The assignments of these spectra are made by the above mentioned method. The 13C chemical shift values of these polypeptide samples are listed together with the reference data of PLA in the right-handed a-helix form and the (3-sheet form, and PLIL in the (3-sheet form in Table 6.21,22,26 The reference 13C chemical shift data were used... 

From the above results, it is very significant to realize that the homopolypeptides of PLA, PDA and PG in the helix form do not form the p-sheet form used by the TFA-alkaline treatment (Method 5) for preparing blend samples. However the conformation of their blend samples, prepared by the TFA-alkaline treatment Method 5), is changed from the a-helix or 31-helix form to the p-sheet form. Further, it can be said that the p-sheet form of PLA, PDA and PG in the blend polymers is incorporated into PLIL and PLV in the p-sheet form. It then takes the p-sheet form by forming hydrogen bonds with PLIL and PLV, and the other components of PLA, PDA and PG take the... 

As an NMR methodology for elucidating miscibility in the PLA/PLV, PLA/PLIL, PDA/PLV and PG/PLV blends, the proton spin-lattice relaxation times in the rotating frame ) for homopolypeptides and their... 

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