Glutamate negative charges

Figure 1.9 Examples of functionally important intrinsic metal atoms in proteins, (a) The di-iron center of the enzyme ribonucleotide reductase. Two iron atoms form a redox center that produces a free radical in a nearby tyrosine side chain. The iron atoms are bridged by a glutamic acid residue and a negatively charged oxygen atom called a p-oxo bridge. The coordination of the iron atoms is completed by histidine, aspartic acid, and glutamic acid side chains as well as water molecules, (b) The catalytically active zinc atom in the enzyme alcohol dehydrogenase. The zinc atom is coordinated to the protein by one histidine and two cysteine side chains. During catalysis zinc binds an alcohol molecule in a suitable position for hydride transfer to the coenzyme moiety, a nicotinamide, [(a) Adapted from P. Nordlund et al., Nature 345 593-598, 1990.)...

Aspartic and glutamic acids are themselves negatively charged under physiological conditions. This allows them to chelate certain metal ions, and also to markedly influence the conformation adopted by polypeptide chains in which they are found. 

Several of the 20 amino acids that constitute the building blocks of proteins exhibit charged side chains. At pH 7.0, aspartic and glutamic acids have overall negatively charged acidic... 

The predominance of aspartate and glutamate residues in the Ca -coordination spheres of proteins was quantified in Section III,D. They constitute 29% and 18%, respectively, of the Ca " -coordinating ligands from the proteins presented in Table II. An analysis of the hydrogenbonding networks around the Ca -binding sites of these proteins (Color Plate 2 and Fig. 7) indicates several reasons for the prevalence of these negatively charged amino acids. The side-chain carboxylate moiety of... 

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