PROSITE documentation PDOC00499

Avidin-like domain signature and profile

Avidin [1] is a minor constituent of egg white in several groups of oviparous vertebrates. Avidin, which was discovered in the 1920's, takes its name from the avidity with which it binds biotin. These two molecules bind so strongly that is highly difficult to separate them. Streptavidin is a protein produced by Streptomyces avidinii which also binds biotin and whose sequence is evolutionary related to that of avidin.

Avidin and streptavidin both form homotetrameric complexes of noncovalently associated chains. Each chain forms a very strong and specific non-covalent complex with one molecule of biotin.

Fibropellins I and III [2] are proteins that form the apical lamina of the sea urchin embryo, a component of the extracellular matrix. These two proteins have a modular structure composed of a CUB domain (see <PDOC00908>), followed by a variable number of EGF repeats (see <PDOC00021>) and a C-terminal avidin-like domain. The fibropellin avidin-like domain forms a homotetramer incapable of binding biotin [3].

The three-dimensional structures of both streptavidin [4,5] and avidin [6] have been determined and revealed them to share a common fold: an eight stranded anti-parallel β-barrel with a repeated +1 topology enclosing an internal ligand binding site (see <PDB:1AVD>).

As a signature sequence for the avidin-like domain we selected a conserved motif located in its C-terminal section. We also developed a profile that covers the entire avidin-like domain.