4gh7
Crystal structure of Anticalin N7A in complex with oncofetal fibronectin fragment Fn7B8
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] Publication Abstract from PubMedThe oncofetal isoform of the extracellular matrix protein fibronectin (Fn), which carries the extra-domain B (ED-B) and is exclusively expressed in neovasculature, has gained interest for tumor diagnosis and therapy using engineered antibody fragments. We have employed the human lipocalin 2 (Lcn2) as a small and robust non-immunoglobulin scaffold to select ED-B-specific Anticalins from a new advanced random library using bacterial phage display and ELISA screening against appropriately engineered Fn fragments. As a result, we have isolated and biochemically characterized four different Anticalins that all show low nanomolar affinities for ED-B, right in the range between the monomeric and dimeric forms of the single-chain variable antibody fragment L19 that has been widely applied in this area before. All Anticalins can be readily expressed in Escherichia coli as soluble and strictly monomeric proteins, and they show specific staining of ED-B-positive tumor cells in immunofluorescence microscopy while BIAcore affinity analyses indicate recognition of distinct ED-B epitopes. The crystal structure for one Anticalin, N7A, in complex with the Fn7B8 fragment, was solved at 2.6A resolution and reveals binding to the gfcc' sheet and cc' loop on ED-B. This is the second example of a protein-specific Lcn2-based Anticalin, which illustrates the remarkable plasticity of the calyx-like ligand pocket of lipocalins with their four structurally hypervariable loops supported by a highly conserved beta-barrel. The ED-B-specific Anticalins resulting from this study should provide useful reagents in research and biomedical drug development, both for in vivo imaging and for directed cancer therapy. Combinatorial Design of an Anticalin Directed against the Extra-Domain B for the Specific Targeting of Oncofetal Fibronectin.,Gebauer M, Schiefner A, Matschiner G, Skerra A J Mol Biol. 2012 Dec 10. pii: S0022-2836(12)00918-7. doi:, 10.1016/j.jmb.2012.12.004. PMID:23238252[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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