| Type: | Family | Name: | Avidin |
| Description: | Avidin [] is a minor constituent of egg white in several groups of oviparousvertebrates. Avidin, which was discovered in the 1920's, takes its name from the avidity with which it binds biotin. These two molecules bind so stronglythat is extremely difficult to separate them. Streptavidin is a protein produced by Streptomyces avidiniiwhich 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-covalentcomplex with one molecule of biotin.The three-dimensional structures of both streptavidin [, ] and avidin [] have been determined and revealed them to share a common fold: an eightstranded anti-parallel beta-barrel with a repeated +1 topology enclosing an internal ligand binding site.Fibropellins I and III [] are proteins that form the apical lamina of the seaurchin embryo, a component of the extracellular matrix. These two proteins have a modular structure composed of a CUB domain (see), followed by a variable number of EGF repeats and a C-terminal avidin-like domain. | Short Name: | Avidin |
