Glutamic acid residues, reactivity

All the evidence presented in this section concerns aspartic acid residues, and one may wonder whether glutamic acid residues display similar reactivity. The answer is clearly that they do not, in particular for entropy reasons. In fact, replacement of a reactive aspartic acid residue by a glutamic acid residue can greatly increase the chemical stability of a peptide. This is exemplified by human epidermal growth factor (hEGF), an important promoter of... 

One approach to the rearrangement problem for carbenes has been partially solved with the use of ethyl 2-diazomalonyl esters which are not as susceptible to rearrangements as diazoacetates (Hexter and Westheimer 1971). Vaughan and Westheimer (1969) have prepared the nitrophenyl ester of ethyl 2-diazomalonate and used it to acylate the reactive serine of trypsin. Photolysis at 253 nm has yielded a glutamic acid residue which presumably arises from the insertion of the... 

Sulphur mustard alkylates the cysteine-34 residue in human serum albumin (Noort et al., 1999, 2004b), which is known to react with a number of electrophiles. This residue is much more accessible than the cysteines in haemoglobin, and its reactivity is promoted by its relatively low pKa, resulting from intramolecular stabilization of the thiolate anion. Aspartic and glutamic acid residues on albumin also react with... 

Trypsin inhibitors in cucumber were first found in a study by Walker-Simmons et /. " after wounding of leaves and treatment with proteinase inhibitor-inducing factor (PIIF). The amino acid sequence of two inhibitors isolated from Cucurhita maxima (winter squash) were determined by Wilusz et at The peptides named ITD I and ITD 111 each comprised a 29-residue sequence with six cysteine residues. The only difference between the two peptides is in position 9, which is lysine in ITD I and glutamic acid in ITD III. The reactive site is located at the peptide bond between Arg5 and Ile6. Owing to their discovery and distribution in Cucurbitaceae the inhibitor family has been named squash inhibitors. Since the initial discoveries many other members of the squash family have been found. 

The functionalization of folded motifs is based on an understanding of secondary and tertiary structures (Fig. 2) and must take into account the relative positions of the residues, their rotamer populations and possible interactions with residues that do not form part of the site. For example, glutamic acid in position i has a strong propensity for salt-bridge formation, and thus reduced reactivity, if there is a Lys residue available i-4 in the sequence, but the probabihty is much less if the base is i-3 [60]. Fortunately, there is a wealth of structural information on the structural properties of the common amino acids from studies of natural proteins that provides considerable support for the design of new proteins. The naturally occurring amino acids have so far been used to construct reactive sites for catalysis [11-13], metal- and heme-binding sites [14,15,19,21,22] and for the site-selective functionalization of folded proteins [24,25]. 

In summary, protein molecules may contain up to nine amino acids that are readily derivatizable at their side chains aspartic acid, glutamic acid, lysine, arginine, cysteine, histidine, tyrosine, methionine, and tryptophan. These nine residues contain eight principal functional groups with sufficient reactivity for modification reactions primary amines, carboxylates, sulfhydryls (or disulfides), thioethers, imidazolyls, gua-nidinyl groups, and phenolic and indolyl rings. All of these side chain functional groups in addition to the N-terminal a-amino and the C-terminal a-carboxylate form the full complement of polypeptide reactivity within proteins (Fig. 12). 

Native CPMV particles display reactive lysines [82], carboxylates derived from aspartic and glutamic acid [83], and tyrosines [84] on their exterior solvent-exposed surface (Figure 9.4). They further display reactive interior cysteines residues [79],... 

The striking successes achieved by Shaw (1970a) and his coworkers with haloketone derivatives of N-tosyl-phenylalanine and a-N-tosyl-lysine as affinity labels for chymotrypsin and trypsin, respectively, have stimulated their use in a large number of affinity labels. Haloketones are potentially reactive with all the nucleophilic amino acid residues in proteins. Examples of residues modified by haloketones include methionine (Sigman et al. 1970), glutamate (Visser et al. 1971), cysteine (Porter et al. 1971), histidine (Schoellman and Shaw 1963) and serine (Schroeder and Shaw 1971). 

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