6gqz
From Proteopedia
Petrobactin-binding engineered lipocalin without ligand
Structural highlights
Function[NGAL_HUMAN] Iron-trafficking protein involved in multiple processes such as apoptosis, innate immunity and renal development. Binds iron through association with 2,5-dihydroxybenzoic acid (2,5-DHBA), a siderophore that shares structural similarities with bacterial enterobactin, and delivers or removes iron from the cell, depending on the context. Iron-bound form (holo-24p3) is internalized following binding to the SLC22A17 (24p3R) receptor, leading to release of iron and subsequent increase of intracellular iron concentration. In contrast, association of the iron-free form (apo-24p3) with the SLC22A17 (24p3R) receptor is followed by association with an intracellular siderophore, iron chelation and iron transfer to the extracellular medium, thereby reducing intracellular iron concentration. Involved in apoptosis due to interleukin-3 (IL3) deprivation: iron-loaded form increases intracellular iron concentration without promoting apoptosis, while iron-free form decreases intracellular iron levels, inducing expression of the proapoptotic protein BCL2L11/BIM, resulting in apoptosis. Involved in innate immunity, possibly by sequestrating iron, leading to limit bacterial growth.[1] Publication Abstract from PubMedBacillus anthracis constitutes a dangerous biohazard which, apart from specific toxins, owes its pronounced virulence to a two-pronged import mechanism for FeIII ions, which are scarce in body fluids. This pathogenic bacterium secretes a pair of siderophores, bacillibactin (BB) and petrobactin (PB), of which only BB is bound and neutralized by the human siderocalin, an abundant lipocalin protein in human plasma. We describe the reshaping of siderocalin by combinatorial and rational protein engineering to specifically bind PB*FeIII instead of BB*FeIII, and with even higher affinity (KD approximately 20 pM). X-ray crystallographic analysis of the resulting "petrocalin" in complex with PB*GaIII reveals a positively charged ligand pocket dominated by two Lys and two Arg side chains, of which Arg100 also forms two hydrogen bonds to the central carboxyl and hydroxyl groups of PB. Furthermore, the extended butterfly-like conformation of the PB metal-chelate complex, first elucidated in this study, provides a rationale for the missing recognition by the natural siderocalin. Finally, microbiological studies demonstrate that a combination of petrocalin and siderocalin effectively suppresses the growth of a BB+/PB+ strain of Bacillus cereus under iron-limiting culture conditions. Thus, our engineered lipocalin may offer novel treatment options for devastating infections caused by B. anthracis. Reprogramming human siderocalin to neutralize petrobactin, the essential iron scavenger of Anthrax bacillus.,Dauner M, Eichinger A, Lucking G, Scherer S, Skerra A Angew Chem Int Ed Engl. 2018 Jul 31. doi: 10.1002/anie.201807442. PMID:30063283[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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Categories: Eichinger, A | Skerra, A | Anticalin | Beta-barrel | Lcn2 | Lipocalin | Ngal | Petrobactin | Protein engineering | Transport protein
