1. Department of Biological Sciences,
2. Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA
3. Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA

Correspondence to: Jue Chen¹ Correspondence and requests for materials should be addressed to J.C. (Email: chenjue@purdue.edu).

Abstract

The maltose uptake system of Escherichia coli is a well-characterized member of the ATP-binding cassette transporter superfamily. Here we present the 2.8-Å crystal structure of the intact maltose transporter in complex with the maltose-binding protein, maltose and ATP. This structure, stabilized by a mutation that prevents ATP hydrolysis, captures the ATP-binding cassette dimer in a closed, ATP-bound conformation. Maltose is occluded within a solvent-filled cavity at the interface of the two transmembrane subunits, about halfway into the lipid bilayer. The binding protein docks onto the entrance of the cavity in an open conformation and serves as a cap to ensure unidirectional translocation of the sugar molecule. These results provide direct evidence for a concerted mechanism of transport in which solute is transferred from the binding protein to the transmembrane subunits when the cassette dimer closes to hydrolyse ATP.

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