STRUCTURAL CLASSIFICATION OF PROTEINS (SCOP)

The complexities of tertiary structure of proteins is decreased by considering substructures. Taking this idea forward researchers have organised complete content of the databases according to hierarchical levels of structure. SCOP, CATH & FSSP are the databases that were developed keeping this in view.

SCOP: Structural Classification Of Proteins

SCOP is a hierarchical classificatiov of proteins. I was first published in 1995 and is usually yearly updated by Alexei G. Murzin and his colleagues upon whose expertise the classification rests.

SCOP is mostly manually curated unlike CATH and FSSP, which make use of automated methods.

Hierarchical Structure:

SCOP has the following Hierarchical levels:

• Class
• Fold
• Superfamily
• Family

The top two levels of organization, Class and Fold are purely structural. Below the fold level, categorization is based on eolutionary relationships.

Class
Class is the top most level in the hierarchical classification. All the protein structures are divided into 4 classes. They are:

1. All α
   
2. All β
3. α/β (α and β segments are either interspersed or present alternatively)
   
4. α + β (α and β segments are sggregated)

Fold
With in every class there are ten to hundreds of folds. Similar arrangement of regular secondary structures is observed.

Family
Proteins with significant primary sequence similarity and demonstrable structural similarity are grouped into one family. Protens within a family have significant structural realtionships.
Proteins within a single family may found in all the 3 domains of life, suggesting a very ancient origin; and some times found only within a group of organisms, suggesting a recent origin.

Superfamily
Protein families that share a little similarity in primary sequence and make use of same major structural motif and have functional similarities are grouped as superfamilies.

SCOP is a power tool to sequence analysis in tracing many evolutionary relationships.