Figure 1.

The distribution of ionizable residues (for example, the side chains of Arg, Lys, His, Asp and Glu) in proteins might reflect adaptations to cellular and intracellular pH. The search for these structural adaptations should consider the important roles of charged residues on the many different functional, structural, physical and biological factors that influenced the evolution of proteins, as indicated here.

Garcia-Moreno Journal of Biology 2009 8:98   doi:10.1186/jbiol199
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