Implementation of a multifunctional logic gate based on folding/unfolding transitions of a protein

Currently there is great interest in the development of (bio)chemical devices that can act as logic gates at the molecular level. In this work we show that the protein cytochrome c (cyt c) can be used to perform a variety of logic operations such as YES, NOT, AND, OR, and XOR. The protein accepts chemical input signals in the form of denaturants that can induce unfolding of the polypeptide chain. These conformational changes lead to alterations of the protein fluorescence intensity which is used as the output signal. The specific type of logic function performed by the protein depends on the types of denaturants and on the solvent conditions used in the experiment. We describe a dialysis cell that can be regarded as a simple hardware version of a protein gate. This device allows reversible switching of the input signals. The operation of this cell is based on a simplified strategy that employs just one type of chemical input signal, namely an aqueous solution of hydrochloric acid. The logic function performed by the device is determined by a “gate controller” (GC) input. © 2002 Elsevier Science B.V. All rights reserved.