Salt bridges
In proteins, salt bridges[1] occur between amino acid side-chains with opposite positive or negative full-electron charges, namely, (at neutral pH) Glu- or Asp- vs. Arg+ or Lys+. They may also occur between ionized organic ligands, such as acetylcholine+ (or example at right: 1cbr), or inorganic ions, such as K+ or SO4=, and amino acid side-chains. A salt bridge is generally considered to exist when the centers of charge are 4 Å or less apart[2]. The center of charge of the arginine sidechain is the zeta carbon[3]. The energetic significance of such complementary charge pairs is a complex function of the local environment. Proteins from thermophiles have more salt bridges than do proteins from mesophiles[4][5]. These additional salt bridges contribute to stability, resisting denaturation by high temperature[6]. ExamplesUltraviolet-B receptorUVR8 is an ultraviolet-B receptor in plants such as Arabidopsis. It is a homodimer that, upon irradiation, dissociates into a monomer involved in transcriptional activation of UV protective proteins[7]. Unexpectedly, high ionic strength was found to dissociate the dimer. The homodimer 4dnw contains many salt bridges and cation-pi interactions at the interface. More.
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Visualization
Putative salt bridges can be displayed by 1cbr.
