4Q4H: TM287/288 in its apo state

ATP binding cassette (ABC) transporters mediate vital transport processes in every living cell. ATP hydrolysis, which fuels transport, displays positive cooperativity in numerous ABC transporters. In particular, heterodimeric ABC exporters exhibit pronounced allosteric coupling between a catalytically impaired degenerate site, where nucleotides bind tightly, and a consensus site, at which ATP is hydrolyzed in every transport cycle. Whereas the functional phenomenon of cooperativity is well described, its structural basis remains poorly understood. Here, we present the apo structure of the heterodimeric ABC exporter TM287/288 and compare it to the previously solved structure with adenosine 5'-(beta,gamma-imido)triphosphate (AMP-PNP) bound at the degenerate site. In contrast to other ABC exporter structures, the nucleotide binding domains (NBDs) of TM287/288 remain in molecular contact even in the absence of nucleotides, and the arrangement of the transmembrane domains (TMDs) is not influenced by AMP-PNP binding, a notion confirmed by double electron-electron resonance (DEER) measurements. Nucleotide binding at the degenerate site results in structural rearrangements, which are transmitted to the consensus site via two D-loops located at the NBD interface. These loops owe their name from a highly conserved aspartate and are directly connected to the catalytically important Walker B motif. The D-loop at the degenerate site ties the NBDs together even in the absence of nucleotides and substitution of its aspartate by alanine is well-tolerated. By contrast, the D-loop of the consensus site is flexible and the aspartate to alanine mutation and conformational restriction by cross-linking strongly reduces ATP hydrolysis and substrate transport.
PDB ID: 4Q4HDownload
MMDB ID: 121565
PDB Deposition Date: 2014/4/14
Updated in MMDB: 2017/12
Experimental Method:
x-ray diffraction
Resolution: 2.527  Å
Source Organism:
Similar Structures:
Biological Unit for 4Q4H: dimeric; determined by author and by software (PISA)
Molecular Components in 4Q4H
Label Count Molecule
Proteins (2 molecules)
ABC Transporter
Molecule annotation
Uncharacterized ABC Transporter Atp-binding Protein Tm_0288(Gene symbol: TM0288)
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB