What is the meaning of the different classification levels?
The CAMPS database provides a hierarchical clustering of α-helical membrane proteins. The SC-clusters (where SC
stands for structurally correlated) constitute the first layer of the whole classification. Members of a SC-cluster are similar
in sequence and have similar transmembrane helix numbers and loop length patterns. They are likely to share the same fold.
The FH-clusters (functionally homogeneous) are subclusters of the SC-clusters containing membrane proteins with the same
or similar domain architecture. MD-clusters (modeling distance) are also subclusters of SC-clusters and their
members share a sequence identity of at least 30%. FH-clusters and MD-clusters together form the second layer of the classification.
Thus, the SC-,FH, and MD-clusters approach different levels: fold, function and modeling distance.