Transthyretin slowly exchanges subunits under physiological conditions: A convenient chromatographic method to study subunit exchange in oligomeric proteins

Transthyretin (TTR) subunits were labeled with a charge-modifying tag to ev aluate the possibility of subunit exchange between tetramers under physiolo gical conditions. Starting with a mixture of two TTR homote-tramers, one ha ving all subunits tagged at the N termini and the ether composed of untagge d subunits, heterotetramer formation as a function of time and temperature was evaluated using ion exchange chromatography. The data indicate that the subunit exchange can occur under native conditions at physiological pH in vitro, albeit slowly. Wild-type TTR exchanges subunits on a timescale of da ys at 37 degreesC and on a timescale of hours at 4 degreesC. The familial a myloid polyneuropathy-associated variant V30M exchanges subunits at the sam e rate as wild-type TTR at 4 degreesC but slower and less efficiently at 37 degreesC. Small molecule tetramer stabilizers abolish TTR subunit exchange , supporting a dissociative mechanism.