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.

We present the first ex vivo images of fresh, native breast tissue obtained from mastectomy specimens using grating interferometry. This technique yields improved diagnostic capabilities when compared with conventional mammography, especially when discerning the type of malignant conversions and their breadth within normal breast tissue. These promising results advance us toward the ultimate goal, using grating interferometry in vivo on humans in a clinical setting.

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′-(β,γ-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.membrane transport | X-ray crystallography | allosteric communication A BC exporters are found in every organism (1, 2). They minimally consist of four domains and exist as homodimers or heterodimers. Two transmembrane domains (TMDs) span the membrane with a total of 12 transmembrane helices and form the substrate permeation pathway by alternating between inward-and outward-oriented states (Fig. S1A). A pair of nucleotide binding domains (NBDs) is connected to the TMDs via coupling helices and drive conformational cycling of the transporter by binding and hydrolysis of ATP, a process which is linked to NBD dimerization and dissociation (3).In their closed state, the NBDs sandwich two ATP molecules at the dimer interface by composite ATP binding sites involving conserved sequence motifs contributed by both subunits (4, 5). The A-loop and Walker A motif of one NBD and the ABC signature motif of the opposite NBD are involved in nucleotide binding. The Walker B glutamate and the switch-loop histidine constitute a catalytic dyad required for ATP hydrolysis (6, 7). In heterodimeric ABC exporters with asymmetric ATP binding sites, these catalytic residues are noncanonical at the degenerate site and ATP is therefore primarily, if not exclusively, hydrolyzed at the consensus site (8). The Q-and D...

We developed new algorithms and a software tool 'Multiple Genome Aligner' (MGA for short) that efficiently computes multiple genome alignments of large, closely related DNA sequences. For example, it can align 85% percent of the complete genomes of six human adenoviruses (average length 35305 bp.) in 159 seconds. An alignment of 74% of the complete genomes of three of strains of E. coli (lengths: 5528445; 5498450; 4639221 approximately bp.) is produced in 30 minutes.