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Chapter 17 : Periplasmic ABC Transporters
Category: Bacterial Pathogenesis; Microbial Genetics and Molecular Biology
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Primary active transporters, such as ATP-binding cassette (ABC) transporters, directly utilize the free energy released upon the hydrolysis of ATP to pump substrates against a concentration gradient. The fundamental biological role of the ABC is to couple the energy of ATP hydrolysis to an impressively large variety of essential biological phenomena comprising not only transmembrane transport but also several non-transport-related processes such as translation elongation, translation regulation, ribosome biogenesis, and DNA repair. The nature of the substrates handled by ABC transporters is extraordinarily wide, including mono-and oligosaccharides, organic and inorganic ions, amino acids and short peptides, iron-siderophores, metals, polyamine cations, opines, and vitamins. The major finding is that the ABC proteins or domains fall into three main subdivisions or classes: class 1 comprises systems with fused ABC and IM domains, class 2 comprises systems with two duplicated fused ABC domains and no transmembrane domains, and class 3 contains systems with IM and ABC domains carried by independent polypeptide chains. It can be speculated that at least some membrane proteins C (BMPCs) might be involved in the uptake of an as-yet unidentified monosaccharide. Genes encoding the ATPase of ABC systems constitute about 2% of total genes in most Bacteria and Archaea. A closer look at the distribution of ABC systems among the sequenced genomes reveals several interesting features. Efforts are required to experimentally analyze in detail the functions of ABC transporters.