Abstract
Bacterial ATP binding cassette (ABC) transporters mediate the influx of numerous substrates. The cluster A-I ABC transporters are responsible for the specific uptake of the essential metals zinc, manganese or iron, making them necessary for survival in metal-limited environments, which for pathogens include the animal host. In Paracoccus denitrificans, there are two zinc ABC transporter systems: ZnuABC and AztABCD with apparently redundant functions under zinc-limited conditions. The unusual presence of two zinc ABC transporter systems in the same organism allowed for the investigation of specificity in the interaction between the solute binding protein (SBP) and its cognate permease. We also assessed the role of flexible loop features in the SBP in permease binding and zinc transport. The results indicate that the SBP–permease interaction is highly specific and does not require the flexible loop features of the SBP. We also present an expanded table of the properties of characterized cluster A-I SBPs and a multiple sequence alignment highlighting the conserved features. Through this analysis, an apparently new family of binding proteins associated with ABC transporters was identified. The presence of homologues in several human pathogens raises the possibility of using it as a target for the development of new antimicrobial therapies.
Highlights
The ATP binding cassette (ABC) transporters are a superfamily of membrane transport proteins with representatives across all kingdoms of life [1]
Prokaryotic ABC transporters are expressed from operons encoding all the necessary components, including a single solute binding protein (SBP) that interacts with its cognate permease
Through the construction of hybrid transporter systems, it was recently shown that the SBP for one ABC transporter could facilitate transport through a related transporter, thereby altering its substrate specificity [8]
Summary
The ATP binding cassette (ABC) transporters are a superfamily of membrane transport proteins with representatives across all kingdoms of life [1] These systems are minimally composed of a membrane spanning permease formed by two transmembrane domains or subunits and an intracellular ATPase formed by two nucleotide binding domains or subunits. Through the construction of hybrid transporter systems, it was recently shown that the SBP for one ABC transporter could facilitate transport through a related transporter, thereby altering its substrate specificity [8] To our knowledge, this is the only example of SBPs that can interact with multiple permeases, suggesting that, in most cases, the permease-SBP interaction is highly specific
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