Tripeptides, structures

P denotes 4-hydroxyproline k denotes fully hydroxylated and glycosylated lysine residues (-) denotes deletions which had to be introduced to ensure optimal matching of the tripeptide structure of both chains. The non-triple-helical sequences are underlined. Three different types of non-triple-helical interruptions have been observed (1) longer nonhelical sequences, expected to create flexible sites sensitive to proteases (2) an extra amino acid in one of the two chains expected to create a bend (3) neutral substitutions expected to disturb only slightly the structure of the triple helix. 

There have been quite extensive SAR studies of the structural requirements for agonists and antagonists activity at formyl receptors, mainly within the tripeptide structure, but no non-peptides have been demonstrated to bind selectively. Analogues known to have high chemotactic activity include N-formyl-Met-Ile-Phe-Leu, N-Acetyl-Met-Leu-Phe, IV-formyl-Met-Leu-lle-Phe and simlar analogues. In contrast, some appear to be inhibitors or antagonists see FORMYL RECEPTOR ANTAGONISTS. 

There are several levels of pepfide sfrucfure The primary structure is the ammo acid sequence plus any disulfide links With the 20 ammo acids of Table 27 1 as building blocks 20 dipeptides 20 tripeptides 20" tetrapeptides and so on are possible Given a peptide of unknown structure how do we determine its ammo acid sequence" ... 

The sequence of amino acids in a peptide can be written using the three-letter code shown in Figure 45.3 or a one-letter code, both in common use. For example, the tripeptide, ala.ala.phe, could be abbreviated further to AAF Although peptides and proteins have chain-like structures, they seldom produce a simple linear system rather, the chains fold and wrap around each other to give complex shapes. The chemical nature of the various amino acid side groups dictates the way in which the chains fold to arrive at a thermodynamically most-favored state. 

Propose two structures for a tripeptide that gives Leu.. Ala, and Phe on hydrolysis but does not react with phenyl isothiocyanate. 

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). 

Fig. 2.26 The crystal structure of / -tripeptide 113 with 1-aminomethylcyclohexanecarboxylic acid residues reveals a 10-membered H-bonded turn segment involving NH of residue 2 and C=0 of residue 3 [145]. The turn segment shows structural similarity to the central 10-membered turn of the 12/10/12-helix (see Section 2.2.3.2 and Fig. 2.19). The intramolecular H-bond is characterized by a N -O distance of 3.10 A and a (N-H -O) angle of 169.4°...

In a study of the three-dimensional structure of thaumatin, it was reported that, not only do antibodies raised against thaumatin cross-react with monellin,but antibodies raised against monellin also cross-react with thaumatin, suggesting that there is some structural similarity between portions of the two sweet-protein molecules. Earlier studies " had shown that there is a limited homology in the amino acid sequence in the two proteins. Five tripeptides in monellin have their counterparts in thaumatin. 

The building blocks for the biosynthesis of benzylpenicillin are three amino acids, a-aminoadipic acid, cysteine and valine, and PAA. The amino acids condense to a tripeptide, ring closure of which gives the penicillin ring structure with an cu-aminoadipyl side-chain, isopenicillin N. The side-chain is then displayed by a phenylacetyl group from PAA to give benzylpenicillin. 

Akamatsu, M. Yoshida, Y. Nakamura, H. Asao, M. Iwamura, H. Fujita, T., Hydrophobicity of di- and tripeptides having unionizable side chains and correlation with substituent and structural parameters, Quant. Struc. -Act. Relat. 8, 195-203 (1989). 

Akamatsu, M. Katayama, T. Kishimoto, D. Kurokawa, Y. Shibata, H., Quantitative analysis of the structure-hydophibicity relationships for n-acetyl di- and tripeptide amides, J. Pharm. Sci. 83, 1026-1033 (1994). 

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