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Publication Abstract from PubMed

The sodium-dependent citrate transporter of Klebsiella pneumoniae (KpCitS) belongs to the 2-hydroxycarboxylate transporter (2-HCT) family and allows the cell to use citrate as sole carbon and energy source in anaerobic conditions. Here we present crystal structures of KpCitS in citrate-bound outward-facing, citrate-bound asymmetric, and citrate-free inward-facing state. The structures reveal that the KpCitS dimerization domain remains stationary throughout the transport cycle due to a hydrogen bond network as well as extensive hydrophobic interactions. In contrast, its transport domain undergoes a ~35 degrees rigid-body rotation and a ~17 A translocation perpendicular to the membrane to expose the substrate-binding site alternately to either side of the membrane. Furthermore, homology models of two other 2-HCT proteins based on the KpCitS structure offer structural insights into their differences in substrate specificity at a molecular level. On the basis of our results and previous biochemical data, we propose that the activity of the 2-HCT CitS involves an elevator-like movement in which the transport domain itself traverses the lipid bilayer, carrying the substrate into the cell in a sodium-dependent manner.

Structural insights into the elevator-like mechanism of the sodium/citrate symporter CitS.,Kim JW, Kim S, Kim S, Lee H, Lee JO, Jin MS Sci Rep. 2017 May 31;7(1):2548. doi: 10.1038/s41598-017-02794-x. PMID:28566738^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.