the amide bond always forms between the ?-carboxyl group of one amino acid and the ?-amino group of the second amino acid. Isopeptide bonds are rarer than regular peptide bonds. Isopeptide bonds lead to branching in the primary sequence of a protein. Proteins formed from normal peptide bonds typically have a linear primary sequence.

Amide bonds, and thus isopeptide bonds, are stabilized by resonance (electron delocalization)