Lipocalin-2/NGAL Protein, Human

Lipocalin-2/NGAL, an iron-trafficking protein, plays a pivotal role in diverse cellular processes, including apoptosis, innate immunity, and renal development. Through its interaction with the siderophore 2,3-dihydroxybenzoic acid (2,3-DHBA), bearing structural resemblance to bacterial enterobactin, Lipocalin-2/NGAL serves as a versatile mediator for the transport of iron into or out of cells, contingent on specific cellular requirements. The iron-bound form (holo-24p3) undergoes internalization upon binding to the SLC22A17 (24p3R) receptor, leading to the liberation of iron and a subsequent rise in intracellular iron concentration. Conversely, the association of the iron-free form (apo-24p3) with the SLC22A17 (24p3R) receptor initiates a cascade involving an intracellular siderophore, resulting in iron chelation and subsequent extracellular iron transfer, ultimately reducing intracellular iron levels. In the context of apoptosis induced by interleukin-3 (IL3) deprivation, the iron-loaded form augments intracellular iron concentration without triggering apoptosis, while the iron-free form diminishes intracellular iron levels, inducing the expression of the proapoptotic protein BCL2L11/BIM, thereby promoting apoptosis. Lipocalin-2/NGAL's involvement in innate immunity manifests as it restricts bacterial proliferation by sequestering iron bound to microbial siderophores, such as enterobactin. Furthermore, Lipocalin-2/NGAL exhibits the ability to bind siderophores from M.tuberculosis. Its structural arrangements include a monomeric state and a homodimer linked by disulfide bonds, as well as a heterodimeric form in association with MMP9.