Biotechnological applications of thermophilic ATP synthase: membrane electronics and genetics

Abstract

Thermophilic membrane proteins are stable and can be incorporated into artificial membranes to carry out special functions. ATP synthase is a central enzyme for energy transformation in biomembranes. Thermophilic ATP synthase was incorporated into a planar lipid bilayer, and its proton current was directly measured. The H +/ATP stoichiometry of thermophilic ATP synthase, which has been the subject of controversy, was shown to be three. Thermophilic ATP synthase consists of a catalytic portion and a proton channel portion. Since its catalytic portion would not bind to the membrane without the proton channel portion, it was covalently connected to a polyvinylbutylal resin membrane on a transistor to detect its signal. In order to improve the physical and catalytic properties of the protein so that it would be more suitable for artificial membranes, an operon for thermophilic ATP synthase was sequenced and mutated. The sitedirected mutagenesis of the a and β subunits revealed that the four ionizable residues corresponding to Lys 21 and Asp 119 in the Mg-ATP binding segments of adenylate kinase are essential for the normal catalytic activity of this enzyme.