Beta bulge loop

Beta bulge loops are commonly occurring motifs in proteins and polypeptides consisting of five to six amino acids.

Compared to other beta bulges, beta bulge loops give rise to chain reversal such that they often occur at the loop ends of beta hairpins; hairpins of this sort can be described as 3:5 (for a type 1 β bulge loop) or 4:6 (for type 2).

[6] Type I beta bulge loops have two characteristic inter-main-chain hydrogen bonds.

Type 2 beta bulge loops have two characteristic inter-main-chain hydrogen bonds.

Beta bulge loops often have an aspartate, asparagine, serine or threonine at residue i, together with a nest (protein structural motif) at residues i+2 to i+4 (type 1) or residues i+3 to i+5 (type 2), with the side chain oxygen binding to the main chain NH groups of the nest.

Type 1 beta bulge loop. Main chain atoms only of hexapeptide; no hydrogen atoms. Carbons grey, oxygens red and nitrogens blue. The two characteristic hydrogen bonds are shown as green and purple lines