Comparison of hydrophobic and strongly hydrophilic cleavable crosslinking reagents in intermolecular bond formation in aggregates of proteins or protein-RNA.

Most of the bifunctional reagents in protein chemistry possess a strongly hydrophobic backbone, derived from aliphatic or aromatic hydrocarbons. Even bifunctionals of more than 30 A in length of this sort form intramolecular bridges preferentially. In recent years, the intermolecular crosslinking of physiological protein aggregates has gained in importance. As shown in the crosslinking of hemoglobin with two sets of hydrophobic and strongly hydrophilic reagents, derived from azo dyes and tartaric acid, respectively, in this case it is not primarily the length of the bifunctional, but the hydrophilic structure that will enhance intermolecular crosslinking. Artificial dimers of native structure may be obtained. For the crosslinking of RNA to protein, we have synthesized a new reagent, 3-(2-bromo-3-oxobutane-1-sulphonyl)-propionic acid p-nitrophenyl ester. In a two step reaction, it is attached to adenine and cytosine moieties at pH 6 first, and to lysine side chains at pH 7,5. The reagent has been applied to the poly-A sequence of globin messenger RNA nucleoprotein.