Alanine hexapeptide

Figure 6 The topological disconnectivity graph of alanine hexapeptide. (Adapted from Ref. 67.)...

Tropoelastin is the soluble precursor of elastin and consists of alternating hydrophobic and hydrophilic peptide domains. The most common amino acids in the hydrophobic domains are Gly, Val, Ala, and Pro, which are often present in repeats of tetra-, penta-, and hexapeptides, such as Gly-Gly-Val-Pro, Gly-Val-Gly-Val-Pro, Gly-Val-Pro-Gly-Val, and Gly-Val-Gly-Val-Ala-Pro, respectively [3, 4]. The hydrophilic domains are mainly composed of lysines interspersed by alanines. 

You have a peptide that is a potent inhibitor of nerve conduction and you wish to obtain its primary sequence. Amino acid analysis reveals the composition to be Ala(5) Lys Phe. Reaction of the intact peptide with FDNB releases free DNP-alanine on acid hydrolysis. e-DNP-lysine (but not a-DNP-lysine) is also found. Tryptic digestion gives a tripeptide (composition Lys, Ala (2)) and a tetrapeptide (composition Ala(3), Phe). Chymotryptic digestion of the intact peptide releases a hexapeptide and free alanine. Derive the peptide sequence. 

Somatostatin is a tetradecapeptide and so is composed of 14 amino acids. The fact that Edman degradation gave the PTH derivative of alanine identifies this as the N-terminal amino acid. A major piece of information is the amino acid sequence of a hexapeptide obtained by partial hydrolysis ... 

Deacylation of deferriferrichrysin occurs in 20 min. in IN HCi at 100°. Trihydrochloride so obtained may be reacylated and, after removal of O-acetyl in methanolic ammonia and re-insertion of iron, ferrichrysin is obtained. The trihydrochloride hexapeptide may be reduced with platinum oxide and H2. Treatment of the latter compound with 2,4-dinitrofluorobenzene followed by hydrolysis gives N8-DNP ornithine. Hydrolysis of ferrichrysin in 57% HI gives serine, glycine, alanine, ornithine and ammonia in the molar ratios 0.24 1.00 1.50 2.91 0.09. Hydrolysis of deferriferrichrysin in 6N HCI, reduction of the hydrolysate with H2 and platinum oxide and addition of excess fluorodinitrobenzene yields crystalline derivatives of glycine, L-serine and L-ornithine. 

We have been more concerned with the nature of the water around proteins and peptides. To this end we have investigated the structure and energetics of the solvent, both ordered and disordered around the enzyme lysozyme, in the triclinic crystal[l7d]. In addition to lysozyme, we have characterized the water structure and fluctuations in the crystal of a cyclic hexapeptide, (L-Ala-L-Pro-D-Phe)9[20]. and studied the effect of solvent on the conformation of the dipeptide of alanine[2l] and on the equilibria between extended and helical alanine polypeptides such as those discussed in the previous section[22]. The latter systems simulate aqueous solution conditions rather than crystalline environment. 

Fig. 4.6 Neurokinin receptor agonist. Substance P is a potent NK receptor agonist. After extensive biological studies, the undecapeptide could be truncated to an active hexapeptide with an improved affinity constant of 11.7 nM. To identify the crucial binding position of the hexapeptide, an alanine scan has been performed. The greatest...

According to the Pep2Lead strategy therefore, the key interaction points within this hexapeptide are investigated, in this case by performing an alanine scan. This technique showed that the replacement of a tryptophan in position 4 impairs inhibition... 

By hydrolysis of RA-VII (153), one D-alanine, two molecules of L-alanine, V-methyl-4-methoxy-L-phenylalanine, and V-methyltyrosine dimer having ether linkage were obtained. RA-VII was assumed to be cyclic hexapeptides consisting of three alanines and three molecules of tyrosine derivatives. From these findings, the structure of RA-VII was assumed to be a bicyclic hexapeptide having ether linkage. However, it was difficult to decide the sequence of amino acids and the configuration... 

It is seen that there is a preponderance of aliphatic chains present long chains contributed by the two leucine fragments, short chains contributed by alanine fragments. The only polar groups are the peptide bonds themselves and the two aromatic rings from the phenylalanine fragments that could produce induced dipoles. It follows that the overall character of the hexapeptide is likely to be dispersive and thus, the peptide would probably be defined as hydrophobic or lyophobic in nature. 

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