The Structural Classification of Proteins (SCOP) database is a largely manual classification of protein structural domains based on similarities of their structures and amino acid sequences. A motivation for this classification is to determine the evolutionary relationship between proteins. Proteins with the same shapes but having little sequence or functional similarity are placed in different superfamilies, and are assumed to have only a very distant common ancestor. Proteins having the same shape and some similarity of sequence and/or function are placed in "families", and are assumed to have a closer common ancestor. Similar to CATH and Pfam databases, SCOP provides a classification of individual structural domains of proteins, rather than a classification of the entire proteins which may include a significant number of different domains. The SCOP database is freely accessible on the internet. SCOP was created in 1994 in the Centre for Protein Engineering and the Laboratory of Molecular Biology. It was maintained by Alexey G. Murzin and his colleagues in the Centre for Protein Engineering until its closure in 2010 and subsequently at the Laboratory of Molecular Biology in Cambridge, England. The work on SCOP 1.75 has been discontinued in 2014. Since then SCOPe team from UC Berkeley has been responsible for updating the database in a compatible manner, with a combination of automated and manual methods. , the latest release is SCOPe 2.07 (March 2018). The new Structural Classification of Proteins version 2 (SCOP2) database was released at the beginning of 2020. The new update featured an improved database schema, a new API and modernised web interface. This was the most significant update by the Cambridge group since SCOP 1.75 and builds on the advances in schema from the SCOP 2 prototype. Hierarchical organisation The source of protein structures is the Protein Data Bank. The unit of classification of structure in SCOP is the protein domain. What the SCOP authors mean by "domain" is suggested by their statement that small proteins and most medium-sized ones have just one domain, and by the observation that human hemoglobin, which has an α2β2 structure, is assigned two SCOP domains, one for the α and one for the β subunit. The shapes of domains are called "folds" in SCOP. Domains belonging to the same fold have the same major secondary structures in the same arrangement with the same topological connections. 1195 folds are given in SCOP version 1.75. Short descriptions of