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Proteins may be classified as to their three-dimensional structure (also known a protein fold). The two most widely used classification schemes are: [2] CATH database [3] Structural Classification of Proteins database (SCOP) [4] Both classification schemes are based on a hierarchy of fold types.
All-β proteins are a class of structural domains in which the secondary structure is composed entirely of β-sheets, with the possible exception of a few isolated α-helices on the periphery. Common examples include the SH3 domain , the beta-propeller domain , the immunoglobulin fold and B3 DNA binding domain .
The words protein, polypeptide, and peptide are a little ambiguous and can overlap in meaning. Protein is generally used to refer to the complete biological molecule in a stable conformation, whereas peptide is generally reserved for a short amino acid oligomers often lacking a stable 3D structure. But the boundary between the two is not well ...
The study of proteins, generally under the heading of proteomics, is a vast and complex subject, and much effort has been made to classify and categorize, according to the many specific fields of investigation under which they come.
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.
The CATH Protein Structure Classification database is a free, publicly available online resource that provides information on the evolutionary relationships of protein domains. It was created in the mid-1990s by Professor Christine Orengo and colleagues including Janet Thornton and David Jones , [ 2 ] and continues to be developed by the Orengo ...
Protein structures range in size from tens to several thousand amino acids. [2] By physical size, proteins are classified as nanoparticles, between 1–100 nm. Very large protein complexes can be formed from protein subunits. For example, many thousands of actin molecules assemble into a microfilament.
These proteins may have different transmembrane topology. [4] [5] These proteins have one of two structural architectures: Helix bundle proteins, which are present in all types of biological membranes; Beta barrel proteins, which are found only in outer membranes of Gram-negative bacteria, and outer membranes of mitochondria and chloroplasts. [6]