Polypeptides polyalanines

The polypeptide polyalanine was synthesized1 and characterized by Matrix Assisted Laser Desorption Ionization (MALDI) and amino acid hydrolyses. Monolayers of either l- or D-polyalanine polypeptides, in the form of an a-helix, were prepared by self-assembly on a borosilicate slide that was coated with a 200-300 nm thick gold film (Metallhandel Schroer Gmbh). Prior to the adsorption, the gold slides were annealed by flame and only then inserted into a 1 mM peptide solution of... 

Fig. 5.17 Histogram of the normal modes calculated for a polyalanine polypeptide in an a-helical conformation. The height of each bar indicates the number of normal modes in each 50cm section.

It is seen that the values of the characteristic ratio estimated by the Stodc-mayer-Fixman method scatter about the Brant-Flory value, tending to increase systematically with monomer molar weight This trend is not in accord with the theoretical prediction (96, 97) that the characteristic ratios of polypeptides having side-chains longer than that of polyalanine should become constant. We... 

The polymerisation of a-aminoacid A-carboxyanhydride, which is accompanied with the elimination of carbon dioxide, constitutes a convenient method for preparing high molecular weight polypeptide. This polymerisation, with the use of a-aminopropionic acid (alanine) A-carboxylic acid anhydride as a monomer, was also carried out in the presence of coordination catalysts such as group 2 and 3 metal alkyls [168-174] or their combinations with water, secondary amine or alcohol [168,173] and yielded polyalanine (Table 9.2). 

The initial conformation of a 100 residue polypeptide of polyalanine was obtained by folding the first 30 residues and last 30 residues as helices the middle 40 residue were folded into a beta-sheet such that both helices were located on the same side of the sheet structure formed as shown in Figure 1. The preliminary structure was passed through limited energy minimization to remove serious contacts and appropriate alanine residues were mutated into glycine at the structural points where appropriate bends occured and where glycine could remove some strain energy. 

Table 15.1 Results obtained from GA and AA for the a-helical and P-pleated sheet configurations of polypeptide constituting polyglycine (A) polyalanine (B)x and 3olyserine (C), residues.

MonomethoxyPEG-polyalanine (mPEG-PA), polyalanine-Poloxamer-polyalanine (PA-PLX-PA) and mPEG-poly(Ala-co-Phe) (mPEG-PAF) were reported as thermogelling polypeptides.As the temperature increased, /3-sheet conformation was partially strengthened and PEG dehydrated. The secondary stmcture of polypeptides plays a role in driving the sol-to-gel transition. 

The same antibodies were not at all inhibited by polylysine or by polyalanine, i.e., by the backbone polypeptide or by the first chain attached. These results again provide strong evidence that the most exposed portion of the molecule, in this case poly(Tyr,Glu), is also the most immunogenic. 

Consider polyglycine or polyalanine. Let us start with an initial U form, which is the fully extended all-trans conformation. The polypeptide starts a motion under the forces originating both from the protein itself and from the solvent. We focus on the latter only. Each change of configuration will in general result in change in G(R ). Some changes will increase G, some will decrease it. 

The inflammatory factor, which has been shown (see p. 69) to be analogous to one of the D-glutamylpolypeptides produced by B. anthracis, also reverses the action of the basic peptide on the respiration of B. anthracis (618). The D-glutamylpolypeptide isolated from B. subtilis possesses the same properties. These phenomena of inhibition of respiration and its reversal, recall the recent observations of Katchalski et al. (340), who showed that the polypeptides resulting from the polymerisation of basic -amino acids (polylysine, polyarginine, and polyornithine) inhibit the growth of St. aureus, E. coli, and B. anthracis, whereas neither polyalanine... 

Synthetic polypeptides were found, by Julia, to epoxidize a, i-unsaturated ketones with high enantioselectivity [12], The Julih process can be easily performed at O C, and using a triphasic system comprising of toluene, water and polyalanine in the presence of alkaline hydrogen peroxide, chalcone oxide was produced in 97% ee (Scheme 1.7). The Julia process has become the method of choice for the epoxidation of fran.y-l,3-diarylenones. However, this methodology is extremely substrate-specific, and enones with enolisable a-protons are usually poor substrates. 

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