Structural Basis of Trans-Inhibition in a Molybdate/Tungstate ABC Transporter

Abstract

Transport across cellular membranes is an essential process that is catalyzed by diverse membrane transport proteins. The turnover rates of certain transporters are inhibited by their substrates in a process termed trans-inhibition, whose structural basis is poorly understood. We present the crystal structure of a molybdate/tungstate ABC transporter (ModBC) from Methanosarcina acetivorans in a trans-inhibited state. The regulatory domains of the nucleotide-binding subunits are in close contact and provide two oxyanion binding pockets at the shared interface. By specifically binding to these pockets, molybdate or tungstate prevent adenosine triphosphatase activity and lock the transporter in an inward-facing conformation, with the catalytic motifs of the nucleotide-binding domains separated. This allosteric effect prevents the transporter from switching between the inward-facing and the outward-facing states, thus interfering with the alternating access and release mechanism.

The Allosteric Regulatory Mechanism of the Escherichia coli MetNI Methionine ATP Binding Cassette (ABC) Transporter

“…The molybdate/tungstate transporter ModBC shares a similar architecture with MetNI and also demonstrates transinhibitory behavior at higher concentrations of substrate (13). The maltose transporter, in contrast, is regulated by an additional protein that responds to nutrient availability.…”

Antigen processing and presentation: TAPping into ABC transporters

“…Therefore these viral inhibitors -US6, UL49.5 and ICP47 -likely all trap TAP in an inward-facing, open-NBDs conformation, blocking the initiation of a transport cycle (Figure 3). This is reminiscent of substrate-mediated trans-inhibition observed for some bacterial ABC importers, in which the transported substrate binds a cytosolic regulatory domain to lock the transporter in the inward-facing, open-NBD conformation when cytoplasmic substrate levels are high [59,60]. The viral TAP inhibitors may function analogously to the regulatory domains of these importers, and by blocking the transporter prior to ATP-driven NBD closure the inhibitors would avoid working against the energy provided by ATP hydrolysis to dissociate the NBDs.…”

Dynamics and Structural Changes Induced by ATP Binding in SAV1866, a Bacterial ABC Exporter

“…All but one correspond to bacterial transporters. Five are ABC importers (BtuCD, ModBC-A, HI1470/1, MalFG/ K, MetNI), [9][10][11][12][13][14][15] and three are drug exporters (SAV1866, MsbA, and mouse P-glycoprotein). [16][17][18][19] High-resolution structures and NMR, EPR, and electron microscopy data strongly suggest that ABC exporters undergo large movements during substrate efflux, in particular upon ATP binding and/or hydrolysis.…”