Crystal structure of a heterodimeric ABC transporter in its inward-facing conformation

Abstract

ATP-binding cassette (ABC) transporters shuttle a wide variety of molecules across cell membranes by alternating between inward- and outward-facing conformations, harnessing the energy of ATP binding and hydrolysis at their nucleotide binding domains (NBDs). Here we present the 2.9-Å crystal structure of the heterodimeric ABC transporter TM287-TM288 (TM287/288) from Thermotoga maritima in its inward-facing state. In contrast to previous studies, we found that the NBDs only partially separate, remaining in contact through an interface involving conserved motifs that connect the two ATP hydrolysis sites. We observed AMP-PNP binding to the degenerate catalytic site, which deviates from the consensus sequence in the same positions as the eukaryotic homologs CFTR and TAP1-TAP2 (TAP1/2). The TM287/288 structure provides unprecedented insights into the mechanism of heterodimeric ABC exporters and will enable future studies on this large transporter superfamily.

Structural basis for antibacterial peptide self‐immunity by the bacterial ABC transporter McjD

“…The NBDs have moved in a “scissors‐like” motion similar to the transition between inward and outward‐open MsbA. A small degree of disengagement between the NBDs has also been reported for the heterodimeric ABC exporter TM287/288 (Hohl et al , 2012; Hohl et al , 2014), ABCG5/8 (Lee et al , 2016) and LptB 2 FG (Luo et al , 2017). …”

Structural and mechanistic insights into prokaryotic energy-coupling factor transporters

“…In contrast to the ATPases, the structures of the integral membrane subunits are not universally conserved among ABC transporters. Four different structural classes have been discovered, which probably have different mechanisms of substrate translocation (see the figure): type I importers (which are exemplified by the maltose transporter MalEFGK 2 from Escherichia coli [57][58][59][60][61] ; Protein Data Bank (PDB) accession 2R6G); type II importers (exemplified by vitamin B 12 transporter BtuC 2 D 2 F from E. coli [62][63][64] ; PDB accession 4FI3); exporters (such as multidrug and peptide transporters [65][66][67] , exemplified by the drug exporter TM287/288) from Thermotoga maritima; PDB accession 3QF4); and ECF transporters (such as ECF-FolT from Lactobacillus brevis for folate transport 21 ; PDB accession 4HUQ). Type I and II importers and energy-coupling factor (ECF) transporters are only found in prokaryotes, whereas exporters are found in all kingdoms of life 28 .…”

“…The proton-coupled lactose transporter LacY is a prominent example of a protein that uses this transport mechanism 71 . Exporters of the ATP-binding cassette (ABC) transporter family might also use a similar mechanism 66,67 . b | Gated-pore mechanism.…”

Conformational dynamics of the ABC transporter McjD seen by single‐molecule FRET

“…All ABC transporters share a common architecture consisting of a transmembrane domain (TMD) for substrate recognition and transport, and a nucleotide‐binding domain (NBD) that converts the chemical energy of ATP into conformational changes for transport (Beis, 2015). The structures of several homodimeric (Dawson & Locher, 2006; Ward et al , 2007; Perez et al , 2015) and heterodimeric ABC transporters (Hohl et al , 2012; Noll et al , 2017) revealed distinct conformations and suggest, in combination with biophysical studies (e.g., EPR and NMR; Dong et al , 2005; Zou et al , 2009; Bountra et al , 2017; Timachi et al , 2017; Barth et al , 2018), that they undergo large conformational changes during transport. Their complex architecture is, however, a fundamental hurdle to fully understand the coupling between conformational changes, substrate binding, ATP binding and hydrolysis, and transport.…”