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Sci Rep. 2016 Sep 15;6:33191. doi: 10.1038/srep33191.

Extension of the classical classification of β-turns.

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INSERM, U 1134, DSIMB, F-75739 Paris, France.
Univ Paris Diderot, Sorbonne Paris Cité, UMR_S 1134, F-75739 Paris, France.
Institut National de la Transfusion Sanguine (INTS), F-75739 Paris, France.
Laboratoire d'Excellence GR-Ex, F-75739 Paris, France.


The functional properties of a protein primarily depend on its three-dimensional (3D) structure. These properties have classically been assigned, visualized and analysed on the basis of protein secondary structures. The β-turn is the third most important secondary structure after helices and β-strands. β-turns have been classified according to the values of the dihedral angles φ and ψ of the central residue. Conventionally, eight different types of β-turns have been defined, whereas those that cannot be defined are classified as type IV β-turns. This classification remains the most widely used. Nonetheless, the miscellaneous type IV β-turns represent 1/3(rd) of β-turn residues. An unsupervised specific clustering approach was designed to search for recurrent new turns in the type IV category. The classical rules of β-turn type assignment were central to the approach. The four most frequently occurring clusters defined the new β-turn types. Unexpectedly, these types, designated IV1, IV2, IV3 and IV4, represent half of the type IV β-turns and occur more frequently than many of the previously established types. These types show convincing particularities, in terms of both structures and sequences that allow for the classical β-turn classification to be extended for the first time in 25 years.

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