Genetically engineered avidins and streptavidins.

Chicken avidin and bacterial streptavidin, (strept)avidin, are proteins widely utilized in a number of applications in life science, ranging from purification and labeling techniques to diagnostics, and from targeted drug delivery to nanotechnology. (Strept)avidin-biotin technology relies on the extremely tight and specific affinity between (strept)avidin and biotin (dissociation constant, K(d) approximately 10(-14)-10(-16) M). (Strept)avidins are also exceptionally stable proteins. To study their ligand binding and stability characteristics, the two proteins have been extensively modified both chemically and genetically. There are excellent accounts of this technology and chemically modified (strept)avidins, but no comprehensive reviews exist concerning genetically engineered (strept)avidins. To fill this gap, we here go through the genetically engineered (strept)avidins, summarizing how these constructs were designed and how they have improved our understanding of the structural and functional characteristics of these proteins, and the benefits they have provided for (strept)avidin-biotin technology.