ATP binding and hydrolysis disrupts the high-affinity interaction between the heme ABC transporter HmuUV and its cognate substrate binding protein [Membrane Biology]

Using the energy of ATP hydrolysis ABC transporters catalyze the trans-membrane transport of molecules. In bacteria they partner with a high affinity substrate binding protein (SBP) to import essential micronutrients. ATP binding by Type-I ABC transporters (importers of amino acids, sugars, peptides, small ions) stabilizes the interaction between the transporter and the SBP, thus allowing transfer of the substrate from the latter to the former. In Type-II ABC transporters (importers of trace elements, e.g., vitamin B12, heme, iron-siderophores) the role of ATP remains debatable. Here we studied the interaction between the Yersinia pestis ABC heme importer (HmuUV) and its partner substrate binding protein (HmuT). Using real-time surface plasmon resonance experiments, and interaction studies in membrane vesicles, we find that in the absence of ATP the transporter and the SBP tightly bind. Substrate in excess inhibits this interaction, and ATP binding by the transporter completely abolishes it. To release the stable docked SBP from the transporter hydrolysis of ATP is required. Based on these results we propose a mechanism for heme acquisition by HmuUV-T where the substrate-loaded SBP docks to the nucleotide-free outward-facing conformation of the transporter. ATP binding leads to formation of an occluded state with the substrate trapped in the trans-membrane translocation cavity. Subsequent ATP hydrolysis leads to substrate delivery to the cytoplasm, release of the SBP, and resetting of the system. We propose that other Type-II ABC transporters likely share the fundamentals of this mechanism.

from # All Medicine by Alexandros G. Sfakianakis via Alexandros G.Sfakianakis on Inoreader http://ift.tt/2vmGh1p
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