Alpha+beta protein fold

Protein classes are broad categories of protein topologies. They describe groups of proteins that share similar amino acid and secondary structure proportions. Each class contains multiple, independent protein superfamilies.

Four large classes of protein that are generally agreed upon by the two main structure classification databases (SCOP and CATH).

An all-α proteins is a class of structural domains in which the secondary structure is composed entirely of α-helices, with the possible exception of a few isolated β-sheets on the periphery.

Common examples include the bromodomain, the globin fold and the homeodomain fold.

An all-β proteins is 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.

α+β proteins are a class of structural domains in which the secondary structure is composed of α-helices and β-strands that occur separately along the backbone. The β-strands are therefore mostly antiparallel.

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