Characterization of Transport through the Periplasmic Histidine Permease Using Proteoliposomes Reconstituted by Dialysis

Abstract

The superfamily of traffic ATPases (ABC transporters) includes bacterial periplasmic transport systems (permeases) and various eukaryotic transporters. The histidine permease of Salmonella typhimurium and Escherichia coli is composed of a membrane-bound complex containing four subunits and of a soluble receptor, the substrate-binding protein (HisJ), and is energized by ATP. The permease was previously reconstituted into proteoliposomes by a detergent dilution method (1Bishop L. Agbayani R.J. Ambudkar S.V. Maloney P.C. Ames G.F.-L. Proc. Natl. Acad. Sci. U. S. A. 1989; 86: 6953-6957Google Scholar). Here we extensively characterize the properties of this permease after reconstitution into proteoliposomes by dialysis and encapsulation of ATP or other reagents by freeze-thawing. We show that histidine transport depends entirely on both ATP and liganded HisJ, with apparent Km values of 8 mM and 8 μM, respectively, and is affected by pH, temperature, and salt concentration. Transport is irreversible and accumulation reaches a plateau at which point transport ceases. The permease is inhibited by ADP and by high concentrations of internal histidine. The inhibition by histidine implies that the membrane-bound complex HisQ/M/P carries a substrate-binding site. The reconstituted permease activity corresponds to about 40-70% turnover rate of the in vivo rate of transport. The superfamily of traffic ATPases (ABC transporters) includes bacterial periplasmic transport systems (permeases) and various eukaryotic transporters. The histidine permease of Salmonella typhimurium and Escherichia coli is composed of a membrane-bound complex containing four subunits and of a soluble receptor, the substrate-binding protein (HisJ), and is energized by ATP. The permease was previously reconstituted into proteoliposomes by a detergent dilution method (1Bishop L. Agbayani R.J. Ambudkar S.V. Maloney P.C. Ames G.F.-L. Proc. Natl. Acad. Sci. U. S. A. 1989; 86: 6953-6957Google Scholar). Here we extensively characterize the properties of this permease after reconstitution into proteoliposomes by dialysis and encapsulation of ATP or other reagents by freeze-thawing. We show that histidine transport depends entirely on both ATP and liganded HisJ, with apparent Km values of 8 mM and 8 μM, respectively, and is affected by pH, temperature, and salt concentration. Transport is irreversible and accumulation reaches a plateau at which point transport ceases. The permease is inhibited by ADP and by high concentrations of internal histidine. The inhibition by histidine implies that the membrane-bound complex HisQ/M/P carries a substrate-binding site. The reconstituted permease activity corresponds to about 40-70% turnover rate of the in vivo rate of transport.