S-peptides

Fig. 11 Experimental set-up for small-scale microwave SPPS of /S-peptides (SPE = solid-phase extraction). 1 Pasteur pipet for N2 agitation 2 10 mL glass vial 3 4mL solid-phase extraction tube 4 DMF 5 coupling solution 6 resin 7 polyethylene frit 8 Luer-lock cap...

A nomenclature was proposed by Seebach for the description of / -amino acids according to their substitution pattern, and for naming the resulting / -peptides [66, 67]. Enantiomerically pure / -amino acid derivatives with substituents in the 2-or 3-position are thus defined as - and / -amino acids, respectively (abbreviated to H-/ -HXaa-OH and H-/ -HXaa-OH). The corresponding /S-peptides built from these monomers will be named ff - and / -peptides. Similarly, /S -peptides consist of / -amino acid residues with substituents in both the 2- and 3-positions. Finally, peptides built from geminally disubsituted amino acids are referred to as and / -peptides (Fig. 2.6). 

A similar sequence of 12- and 10-membered turns is present in the structure of Boc-protected /S //S -peptides 96 and 97, the C=0 of the Boc group being engaged in the first 12-membered ring with NH of residue 3. The pattern of 10- and 12-membered turns is reversed for the fully protected / // -peptide 94 as well as the unprotected /S //S -dodecapeptide 98 which thus folds into a 10/12-helix, with the NH of residues 1 and 2, respectively being involved in the formation of an N-ter-minal 10-membered turn. 

Figure 1 Stages of amyloid aggregation steps in protein polymerization and the techniques used to measure them for the Alzheimer s [ peptide.

Han H, Weinreb PH, Lansbury PT Jr. The core Alzheimer s peptide NAC forms amyloid fibrils which seed and are seeded by beta-amyloid is NAC a common trigger or target in neurodegenerative disease Chem Biol 1995 2 163-169. 

Straub, J.E. Rashkin, A. Thirumalai, D., Dynamics in rugged energy landscapes with applications to the S-peptide and Ribonuclease A, J. Am. Chem. Soc. 1994,116, 2049... 

Bond, J. P., Deverin, S. P., Inouye, H., el-Agnaf, O. M., Teeter, M. M., and Kirschner, D. A. (2003). Assemblies of Alzheimer s peptides A beta 25—35 and A beta 31-35 Reverse-turn conformation and side-chain interactions revealed by X-ray diffraction./. Struct. Biol. 141, 156-170. 

D Sahal. Removal of iodine by solid phase adsorption to charcoal following iodine oxidation of acetamidomethyl-protected peptide precursors to their disulfide bonded products oxytocin and a Pre-S, peptide of hepatitis B illustrate the method. Int J Pept Res 53, 91, 1999. 

Tirado-Rives ). and Jorgensen W. L. Molecular dynamics simulations of the unfolding of an alpha-helical analogue of ribonuclcase A S-peptide in water. Biochemistry (1991) 30(16) 3864-71. 

This enzyme (RNase A) is a single chain protein of 124 amino acid residues, cross-linked by four intrachain disulfide bonds. Limited proteolysis of the enzyme cuts a single peptide bond between residues 20 and 21 (Richards and Vithayathil, 1959). The derived protein, RNase S, retains enzymic activity although the N-terminal peptide of 20 amino acids (S-peptide) is no longer covalently attached to the balance of the molecule (S-protein). Removal of S-peptide from... 

Fig. 3. Inactivation of S-protein, by disulfide interchange in the absence, and subsequent reactivation in the presence, of S-peptide. The reaction was carried out with...

Hg/ml A------A, none. Stabilization against denaturation by S-peptide, 134 ftg/ml, interchange enzyme (A-------A). All reactions were carried out in 0.1 M Tris-chloride... 

S-protein leads to loss of enzymic activity. Activity is rapidly restored upon mixing of S-protein and S-peptide. 

Fig. 1. Schematic drawing of the polypeptide backbone of ribonuclease S (bovine pancreatic ribonuclease A cleaved by subtilisin between residues 20 and 21). Spiral ribbons represent a-helices and arrows represent strands of /3 sheet. The S peptide (residues 1-20) runs down across the back of the structure.

Fig. 9. Proposed structure for the semisynthetic RNase-S complex incorporating the Pal residue. S-peptide shown in dark gray. Reproduced with permission from J Am Chem Soc (1994)116 12084...

In the S-peptide design, the Pal residue was introduced at position 8, replacing the native phenylalanine (Fig. 9) [22]. Lysine residues, which have the potential to form Schiff bases with the pyridoxal functionahty, and a potentially oxidatively unstable methionine residue were replaced with either norleucine or glycine. These changes resulted in a modified S-peptide that associated with S-protein at levels comparable to the original S-peptide. 

Fig.n.9 Deconvolved mass spectra [deconvolution by a maximum entropy algorithm (MaxEnt) supplied by instrument manufacturer] for S-peptide and S-protein, showing differences upon oxidation with 15 mM H2O2 using 15 mM Gin as scavenger. 

B) S-peptide oxidized while bound to RNase S protein, showing less oxidation. (C) RNase S protein oxidized in absence of peptide. (D) RNase S-protein oxidized while bound to S-peptide. 

A second method of incorporating phase into the selection process is to immobilize the target. Essentially an affinity chromatographic method, this allows nonbound library constituents to be washed away, leaving the selected compound(s) bound to resin. Eliseev s guanidine resin and Still s peptide-bearing beads, both discussed above in the context of exchange reactions, are examples of these. 

The ruthenium catalysts have also been attached to various solid supports, including nolyethy-leneglycol (PEG), " mesoporous molecular sieves, " and Merrifield s peptide resin. " ... 

Ohno, M., Tsuchiya, T., Miyake, T., Umezawa, S., "Peptides Synthesis-Structure-Function", p. 29 Proceedings of the 7th American Peptide Symposium, 1981. 

The solid-phase method was tested with the synthesis of many small peptides,[19] including bradykinin, angiotensin, desaminooxytocin, and the 20-residue S-peptide of ribonuclease A, and was found to be useful and efficient. 

It was known from the work of Richards that RNase A could be cleaved between residues 20 and 21 by digestion with subtilisin. 29 The N-terminal 20-residue peptide (S-peptide) could be separated from the 104-residue 21-124 protein (S-protein), and each was enzymatically inactive however, when they were mixed in a 1 1 ratio, full RNase activity was regenerated even though the covalent bond between residues 20 and 21 was not re-formed. This finding was the basis for a great many structure/function studies by the synthesis of analogues of the S-peptide and their noncovalent recombination with natural S-protein.13"31 ... 

Scheme 9 A Three-Dimensional Representation of RNase A, Showing the Relationship of the S-Peptide (1-20), C-Peptide (111-124), S-Protein (21-124), and Shortened S-Protein Derivatives12413...

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