1x8u
From Proteopedia
Crystal structure of Siderocalin (NGAL, Lipocalin 2) complexed with Carboxymycobactin T
Structural highlights
FunctionNGAL_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] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedSiderocalin, a member of the lipocalin family of binding proteins, is found in neutrophil granules, uterine secretions, and at markedly elevated levels in serum and synovium during bacterial infection; it is also secreted from epithelial cells in response to inflammation or tumorigenesis. Identification of high-affinity ligands, bacterial catecholate-type siderophores (such as enterochelin), suggested a possible function for siderocalin: an antibacterial agent, complementing the general antimicrobial innate immune system iron-depletion strategy, sequestering iron as ferric siderophore complexes. Supporting this hypothesis, siderocalin is a potent bacteriostatic agent in vitro under iron-limiting conditions and, when knocked out, renders mice remarkably susceptible to bacterial infection. Here we show that siderocalin also binds soluble siderophores of mycobacteria, including M. tuberculosis: carboxymycobactins. Siderocalin employs a degenerate recognition mechanism to cross react with these dissimilar types of siderophores, broadening the potential utility of this innate immune defense. Siderocalin (Lcn 2) also binds carboxymycobactins, potentially defending against mycobacterial infections through iron sequestration.,Holmes MA, Paulsene W, Jide X, Ratledge C, Strong RK Structure. 2005 Jan;13(1):29-41. PMID:15642259[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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