Binding site conformation dictates the color of the dye stains-all. A study of the binding of this dye to the eye lens proteins crystallins

Abstract

The interaction of the cationic carbocyanine dye Stains-all (1-ethyl-2-[3-(1-ethyl-naphthol[1,2-d]thiazolin-2-ylidene)-2- methylpropenyl]naphthol[1,2-d]thiazolium bromide) with the eye lens proteins crystallins has been studied. α- and γ-crystallins do not bind the dye, while β- and δ-crystallins do, consistent with the fact that the latter two proteins bind the calcium ion. β-Crystallin resembles parvalbumin in that it induces only the J-band of the bound dye. δ-crystallin, on the other hand, induces only the γ-band. Analysis of the metachromasia induced in the dye by these and other proteins suggests that Stains-all is responsive to the conformational status of the region to which it binds in a protein. The J-band of the dye is activated when it binds to a globular domain, and the γ-band is activated when it binds to a helical stretch of the protein.