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Institute
Members of the ATP‐binding cassette (ABC) transporter superfamily translocate a broad spectrum of chemically diverse substrates. While their eponymous ATP‐binding cassette in the nucleotide‐binding domains (NBDs) is highly conserved, their transmembrane domains (TMDs) forming the translocation pathway exhibit distinct folds and topologies, suggesting that during evolution the ancient motor domains were combined with different transmembrane mechanical systems to orchestrate a variety of cellular processes. In recent years, it has become increasingly evident that the distinct TMD folds are best suited to categorize the multitude of ABC transporters. We therefore propose a new ABC transporter classification that is based on structural homology in the TMDs:
The purification and functional reconstitution of a five-component oligopeptide ATP-binding cassette transporter with a remarkably wide substrate specificity are described. High-affinity peptide uptake was dependent on liganded substrate-binding protein OppA, which interacts with the translocator OppBCDF with higher affinity than unliganded OppA. Transport screening with combinatorial peptide libraries revealed that (i) the Opp transporter is not selective with respect to amino acid side chains of the transported peptides; (ii) any peptide that can bind to OppA is transported via Opp, including very long peptides up to 35 residues long; and (iii) the binding specificity of OppA largely determines the overall transport selectivity.