page_title: Siderocalin
section_title: Mycobacterial virulence
hierarchical_section_title: Siderocalin / Clinical significance / Mycobacterial virulence
caption_attribution_description: Structure of Catecholate-Iron-Complex
context_page_description: Siderocalin, lipocalin-2, NGAL, 24p3 is a mammalian lipocalin-type protein that can prevent iron acquisition by pathogenic bacteria by binding siderophores, which are iron-binding chelators made by microorganisms.
  Iron serves as a key nutrient in host-pathogen interactions, and pathogens can acquire iron from the host organism via synthesis and release siderophores such as enterobactin.
  Siderocalin is a part of the mammalian defence mechanism and acts as an antibacterial agent.
  Crystallographic studies of Scn demonstrated that it includes a calyx, a ligand-binding domain that is lined with polar cationic groups.
  Central to the siderophore/siderocalin recognition mechanism are hybrid electrostatic/cation-pi interactions.
  To evade the host defences, pathogens evolved to produce structurally varied siderophores that would not be recognized by siderocalin, allowing the bacteria to acquire iron.
context_section_description: Siderophores are iron chelators, allowing organisms to acquire iron from their environment.  In the case of pathogens, iron can be acquired from the host organism.    
  Siderophores and ferric iron can associate to form stable complexes.  Siderophores bind iron using a variety of ligands, most commonly as α-hydroxycarboxylates (e.g. citrate), catecholates, and hydroxamates. 
  As a defence mechanism, siderocalin can substitute ferric bis-catechol complexes (formed under physiological conditions) with a third catechol, in order to achieve a hexacoordinate ferric complex, resulting in higher affinity binding.
caption: Catecholate-iron binding.  A typical complex would exhibit three such interactions.
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