What Causes Beta Turns

Turns generally occur when the protein chain needs to change direction in order to connect two other elements of secondary structure. The most common is the beta turn, in which the change of direction is executed in the space of four residues.

Where do beta turns occur?

Beta turns are especially common at the loop ends of beta hairpins; they have a different distribution of types from the others; type I’ is commonest, followed by types II’, I and II.

Where might bends or β turns occur?

(a) Bends or turns are most likely to occur at residues 7 and 19 because Pro residues are often (but not always) found at bends in globular folded proteins. A bend may also occur at the Thr residue (residue 4) and, assuming that this is a portion of a larger polypep- tide, at the Ile residue (residue 1).