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.
- Mainly Alpha
- Mainly Beta
- Alpha Beta
- 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.
Michie AD, Orengo CA, Thornton JM
J Mol Biol262p168-85(1996 Sep 20)