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Lipocalin-1

Structure
Proteins are classified into the lipocalin family by their 8 antiparallel beta-sheets that form a barrel structure which acts as the binding site for ligands.

Function
Lipocalin-1 (Lnc1) is capable of binding a wide variety of lipophilic molecules along with zinc and chloride ions. Because of this feature, Lcn1’s main function is thought to be the removal of potentially harmful lipids and lipophilic molecules from the body by binding them and then being imported via lipocalin-1-interacting membrane receptor (LIMR) so the bound molecule can be broken down. This process may impact several other processes including pheromone signaling, immunodulation, inflammation, detoxification, tissue development, apoptosis and more.

Lcn1 shares three sequence motifs with cystatins which enables Lcn1 to also act in a similar manner to the cystatins as a cysteine proteinase inhibitor.

Lcn1 also plays a role in stabilizing the lipid layer of the tear film, though the details of this are not yet well understood.

History
Lipocalin-1 was initially thought to be produced by exocrine glands only but has also been found in corticotrophs of the pituitary gland.

Alternate Names: Human Tear Prealbumin, Tear Lipocalin, von Ebner’s Gland Protein

Clinical
When a cell is under stress, due to inflammation, infection, or otherwise, it will produce elevated levels of lipocalin-1 (Lnc1). This makes it a potential noninvasive biomarker for various diseases. This potential has been shown in a study of IVF blastocysts, where elevated levels of Lcn1 indicated aneuploidy in the blastocyst.

Lipocalin-1 Resources:

https://journals.sagepub.com/doi/full/10.1177/002215540205000314

https://www.jbc.org/content/278/18/16209.short

Hof, W. ’., Blankenvoorde, M. F. J., Veerman, E. C. I., & Amerongen, A. V. N. (1997). The Salivary Lipocalin Von Ebner’s Gland Protein Is a Cysteine Proteinase Inhibitor. Journal of Biological Chemistry, 272(3), 1837–1841. https://doi.org/10.1074/jbc.272.3.1837

Saaren-Seppa¨la¨, H., Jauhiainen, M., Tervo, T. M. T., Redl, B., Kinnunen, P. K. J., & Holopainen, J. M. (2005). Interaction of Purified Tear Lipocalin with Lipid Membranes. Investigative Opthalmology & Visual Science, 46(10), 3649. https://doi.org/10.1167/iovs.05-0176

Nagyová, B., & Tiffany, J. M. (1999). Components responsible for the surface tension of human tears. Current Eye Research, 19(1), 4–11. https://doi.org/10.1076/ceyr.19.1.4.5341

McReynolds, S., Vanderlinden, L., Stevens, J., Hansen, K., Schoolcraft, W. B., & Katz-Jaffe, M. G. (2011). Lipocalin-1: a potential marker for noninvasive aneuploidy screening. Fertility and Sterility, 95(8), 2631–2633. https://doi.org/10.1016/j.fertnstert.2011.01.141

Wojnar, P., Lechner, M., & Redl, B. (2003). Antisense Down-regulation of Lipocalin-interacting Membrane Receptor Expression Inhibits Cellular Internalization of Lipocalin-1 in Human NT2 Cells. Journal of Biological Chemistry, 278(18), 16209–16215. https://doi.org/10.1074/jbc.m210922200

Wojnar, P., Dirnhofer, S., Ladurner, P., Berger, P., & Redl, B. (2002). Human Lipocalin-1, a Physiological Scavenger of Lipophilic Compounds, Is Produced by Corticotrophs of the Pituitary Gland. Journal of Histochemistry & Cytochemistry, 50(3), 433–435. https://doi.org/10.1177/002215540205000314

Wojnar, P., Hof, W. v., Merschak, P., Lechner, M., & Redl, B. (2001). The N-Terminal Part of Recombinant Human Tear Lipocalin/von Ebners Gland Protein Confers Cysteine Proteinase Inhibition Depending on the Presence of the Entire Cystatin-Like Sequence Motifs, Biological Chemistry, 382(10), 1515-1520. doi: https://doi.org/10.1515/BC.2001.186

https://www.semanticscholar.org/paper/Interaction-of-uteroglobin-with-lipocalin-1-cancer-Zhang-Kim/db6c584fc43a51be678d2caa3f652c6c22a5fdb2

https://www.jbc.org/content/276/23/20206.short