Amino-acid residues glutamyl

Recent research has suggested that short synthetic peptides containing different analogs of the first 19-23 amino acid residues of influenza hemaglutinin protein (HA) terminus may be attractive because of their pH-dependent lytic properties, with little activity at pH 7 but > 100-fold increase in transfection efficiency at pH 5. The lytic characteristics are revealed as the carboxyl groups of the aspartyl and glutamyl side chains are protonated, which allows the peptides to assume a a-helical conformation that can be inserted into the membrane bilayer. 

Two amino acid residues are involved in the deamidation reaction asparagyl and glutamyl. The conversion to the corresponding carboxylic acid residues results in... 

Asparagyl residues tend to be more susceptible to deamidation than glutamyl residues. Further, the deamidation reaction is strongly sequence-specific in model peptides with the half life of the -Asn-Pro- sequence being 100-fold greater than that of -Asn-Gly-. To some extent these observations can also be used on proteins that take the structural steiic factors and nearby amino acid residues into consideration. 

Figure 6-1. A peptidoglycan structure. (R is an L-alanyl-D-glutamyl-L-lysyl-D-alanine D-amino acid residues occur here.)...

Some slight modifications of this unit also occur in nature (65) Here, only two will be mentioned, namely those in which the a-amide function of the D-glutamyl residue has been replaced by an amino acid residue, and those in which the L-lysyl residue has been replaced by an a,8-diaminopimelyl residue. Synthetic glycopeptides related to these structures have been reported. 

Oxidation of the polypeptide chain of proteins can also lead to the cleavage of peptide bonds. Two different mechanisms are proposed, a-amidation and diamide pathways (Figure 2.29). In both pathways, the polypeptide chain is shortened and the N- and C-amino acid residues of the resulting fragments are modified (aspartyl, glutamyl and prolyl residue produce specific N- and C-terminal fragments). 

Thr, Glu-Gly, Glu-Ser, Ala-Glu, Gly-Glu, Gly-Glu-Gly, Glu-Glu, and Glu-Asp were found. These polar peptides were reported to elicit a savory umami taste [7,27-29]. Frerot and coworkers [30] identified small peptides in Parmesan cheese. They observed that tripeptides such as Glu-Leu-Glu or Glu-Asp-Phe consisting of a hydrophobic amino acid residue and at least one acidic and one either acidic or hydrophilic amino acid residue impart mouthfeel and umami taste to foods and could replace MSG to some extent. Van den Oord and van Wassenaar [31], however, discuss glutamyl di- and tripeptides controversially and generally question the existence of glutamate-like-tasting peptides. 

Aside from the Maillard reaction, other covalent modifications of amino acids and proteins are possible within the caries lesion, which merit future investigation. For example, certain oral microorganisms excrete y-glutamyl transferases. These enzymes catalyse the formation of cross-links between glutamic acid and lysine residues of proteins. In addition, N-acyl amino acids are present in plaque, which adsorb to mineral surfaces. 

A series of derivatives of the ester 37, having amino acid or peptide residues linked through the carboxyl group of the lactic acid residue, has been described. Their exact structures depend on the growth conditions and the bacterial strain used. The chain attached may contain L-alanine 7,151,154,155 the dipeptide L-alanyl-D-glutamic acid 156,157 the tripeptides L-alanyl-y-D-glutamyl-L-lysine,157-160 L-al-... 

Phosphorylation occurs in the Golgi membranes of the mammary cell, catalysed by two serine-specific casein kinases. Only certain serines are phosphorylated the principal recognition site is Ser/Thr.X.Y, where Y is a glutamyl and occasionally an aspartyl residue once a serine residue has been phosphorylated, SerP can serve as a recognition site. X may be any amino acid but a basic or a very bulky residue may reduce the extent of phosphorylation. However, not all serine residues in a suitable sequence are phosphorylated, suggesting that there may be a further topological requirement, e.g. a surface location in the protein conformation. 

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