Salt bridges
|
In proteins, salt bridges 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 Cl-, and amino acid side-chains.
A salt bridge is generally considered to exist when the centers of charge are 4 Å or less apart[1]. The center of charge of the arginine sidechain is the zeta carbon[2]. The energetic significance of such complementary charge pairs is a complex function of the local environment.
Putative salt bridges can be displayed by FirstGlance in Jmol.
