This is the highest level of classification and is derived from the gross secondary structure content. There are 4 classes defined in the CATH classification.

  1. Mainly Alpha
  2. Mainly Beta
  3. Alpha Beta
  4. Few Secondary Structures.

The classification of protein domains into these 4 classes has been achieved for 90% of structures automatically, using an automated class assignment protocol. This classification protocol includes a number of criteria:

  • Percentage composition of secondary structures
  • Percentage of secondary structures contacts
  • Secondary structure alternation
  • Percentage of parallel strands

This is discussed in detail in the paper referenced below.


Analysis of domain structural class using an automated class assignment protocol.
Michie AD, Orengo CA, Thornton JM
J Mol Biol262p168-85(1996 Sep 20)