Tripeptide sequence

H-Tyr-D-Ala-Pile-Asp-Val-Val-Gly-NH2 (D-Ala -deltorpliiu I) and H-Tyr-D-Ala-Plie-Glu-Val-Val-Gly-NH2 (D-Ala -deltorpliiu II) display greater 5-selectivity than DPDPE owiag to their higher 5-receptor affinity (96). These compounds both contain the same N-terminal tripeptide sequence as the. -selective dermorphins, which underscores the importance of the C-terminal tetrapeptide sequence in conferring 5-selectivity. 

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 availability of high-resolution structures of peptides EKG, T3-785, IBP, and G991-G1032, which include residues other than Pro and Hyp in the X and Y positions, offers the opportunity to investigate the conformation and interactions of side chains from residues typically found within the collagen triple helix. In the peptide with an EKG tripeptide sequence, the Lys and Glu residues did not form direct intermolecular or intramolecular ion pairs, even though such pairs are sterically feasible. ... 

Gramicidin S is a cyclic decapeptide with a characteristic CD spectrum that qualitatively resembles that of an a-helixj185-189 but numerous studies described below strongly support the structure predicted by Hodgkin and O ugh ton11751 and by Schwyzer et alJ176l in which 13-turns (type II ) at the D-Phe-L-Pro sequences link two extended tripeptide sequences (Val-Orn-Leu) that form an antiparallel (3-structure. 

FIGURE 9.6 Structure features of integrin receptors. Peptides or proteins containing the tripeptide sequence of RGD are recognized by several integrins present in the tumor cells. However, the protein tails pass through the plasma membrane with the hydrophobic domains and are locked into place. (From dos Santos, 2005)... 

When synthetic peptides were used as acceptors for N-glycosylation from GlcNAc2-PP-Dol, the necessity for the tripeptide sequence Asn-X-Ser/Thr could be demonstrated. Moreover, the rate of glycosylation was affected by the chain length of the peptides. Other factors, such as hydrophobicity and steric hindrance, have different effects on the acceptor properties of the peptides, as judged by the results of (2,4-dinitrophenyl)ation and dansyl-ation of them.134... 

Collagen has a most unusual amino acid composition in which glycine, proline, and hydroxyproline are the dominant amino acids. Further characterization of the polypeptide chains shows that these amino acids are arranged in a repetitious tripeptide sequence, Gly-X-Y, in which X is frequently a proline and Y is frequently a hydroxyproline. This unusual amino acid sequence and the unique diffraction pat-... 

Recall that collagen is an extracellular matrix protein that serves as a major constituent of many connective tissues (see figs. 4.10 to 4.13). Collagen fibrils have a distinctive banded pattern with a periodicity of 680 A. Individual fibrils are composed of three polypeptide chains wound around one another in a right-handed helix with a total length of 3,000 A. Each of the polypeptide chains in the triple helix has a repetitious tripeptide sequence, Gly-X-Y, where X is frequently a proline and Y is frequently a hy-droxyproline. The latter amino acid is not one of the 20 that are specified genetically, so it must be formed posttransla-tionally by a modification of some of the prolines. 

An interesting correlation between tripeptide sequences and genetic mutations has been made by compilation of the number of occurrences of the tripeptide sequence Asn—B—Ser and Asn—B—Thr in protein sequence-data at present available from the literature.134 A total of 18,251 tripeptide sequences from 264 proteins was grouped by computer into the 400 possible tripeptide combinations of the 20 amino acids in which the second position was ignored. The total number of Asn—B—(Ser/Thr) sequences actually present in these proteins was 61, whereas the total number theoretically expected, on the basis of a random distribution within the sequence, would have been 102. The observed data were thus lower than expected by 4 standard deviations. On the other hand, such chemically similar tripeptides as Gin—B—(Ser/Thr), Asp—B—(Ser/Thr), and (Ser/Thr)—B—Asn occurred the number of times expected for random distribution. It was suggested that this low frequency of incidence of the Asn—B—(Ser/Thr) sequence results from a restriction of its occurrence in proteins by a process of natural selection. Any protein that acquired this tripeptide as a result of a mutation would be soon rejected, because carbohydrate would be bound to the asparagine residue and its presence would interfere with the normal metabolic function of the protein. 

The C-exposed library L35c was screened for its binding affinity for the guanidinium-based, fluorescent tweezer receptor 9.135 (225), whose structure is reported in Fig. 9.50. The dansylated chains should have assured the fluorescent detection of beads containing ligand tripeptidic sequences, and a series of control experiments ruled out the possibility of significant, nonspecific interaction of the beads with the receptor or with the biological assay constituents. The assay conditions were carefully optimized, and around 7000 beads (seven library equivalents, complete representation of the library individuals) were incubated with 9.135. 

A number of recent approaches to the discovery of orally active thrombin inhibitors have their origins in the tripeptide sequence D - Phe - Pro - Arg. 

Knichal, 1962). Both approaches indicate that there is no general preference for any particular dipeptide sequence or sequences. It also seems likely that there will be no forbidden tripeptide sequences since of the 8000 possible combinations of three amino acids as many as 1032 had already... 

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