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Conformational plasticity of the type I maltose ABC importer

Publication date2013-03-18
First online date2013-03-18
Abstract

ATP-binding cassette (ABC) transporters couple the translocation of solutes across membranes to ATP hydrolysis. Crystal structures of the Escherichia coli maltose importer (MalFGK 2 ) in complex with its substrate binding protein (MalE) provided unprecedented insights in the mechanism of substrate translocation, leaving the MalE–transporter interactions still poorly understood. Using pulsed EPR and cross-linking methods we investigated the effects of maltose and MalE on complex formation and correlated motions of the MalK 2 nucleotide-binding domains (NBDs). We found that both substrate-free (open) and liganded (closed) MalE interact with the transporter with similar affinity in all nucleotide states. In the apo-state, binding of open MalE occurs via the N -lobe, leaving the C-lobe disordered, but upon maltose binding, closed MalE associates tighter to the transporter. In both cases the NBDs remain open. In the presence of ATP, the transporter binds both substrate-free and liganded MalE, both inducing the outward-facing conformation trapped in the crystal with open MalE at the periplasmic side and NBDs tightly closed. In contrast to ATP, ADP–Mg 2+ alone is sufficient to induce a semiopen conformation in the NBDs. In this nucleotide-driven state, the transporter binds both open and closed MalE with slightly different periplasmic configurations. We also found that dissociation of MalE is not a required step for substrate translocation since a supercomplex with MalE cross-linked to MalG retains the ability to hydrolyze ATP and to transport maltose. These features of MalE–MalFGK 2 interactions highlight the conformational plasticity of the maltose importer, providing insights into the ATPase stimulation by unliganded MalE.

eng
Affiliation Not a UNIGE publication
Citation (ISO format)
BÖHM, Simon et al. Conformational plasticity of the type I maltose ABC importer. In: Proceedings of the National Academy of Sciences of the United States of America, 2013, vol. 110, n° 14, p. 5492–5497. doi: 10.1073/pnas.1217745110
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ISSN of the journal0027-8424
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