### DipCheck online

DipCheck is a validation tool for the evaluation of protein backbone geometry, developed by Joana Pereira and Victor Lamzin at the EMBL Hamburg.

The tool uses a Euclidian 3D space (DipSpace) of the orthogonal descriptors of the geometry of a 5-atom dipeptide unit: CA_{i-1}-O_{i-1}-CA_{i}-O_{i}-CA_{i+1}. The DipSpace database contains 1,024,000 data points derived from well-refined structures deposited in the PDB.

DipCheck classifies the geometry of a given **CA (CA _{i}) atom **in four categories:

Favoured region | 98.00% of the set, DipScore above 0.243 |

Allowed region | 99.80% of the set, DipScore between 0.243 and 0.033 |

Generously allowed region | 99.95% of the set, DipScore between 0.033 and 0.010 |

Disallowed region | the remaining 0.05%, DipScore below 0.010 |

DipCheck also classifies the overall **geometry of a protein model**, according to its DipScore distribution, in four categories:

Favoured model | 98.00% of a random set of protein models, Chi-score above -2.16 |

Allowed model | 99.80% of a random set of protein models, Chi-score between -2.97 and -2.16 |

Generously allowed model | 99.95% of a random set of protein models, Chi-score between -3.38 and -2.97 |

Outlier model | the remaining 0.05%, Chi-score below -3.38 |