Lipokaline

Lipocalins are a large, inhomogeneous family of small (molecular weight of 16-22kDa), inhomologous proteins that occur everywhere in nature, such as in animals, plants and bacteria. Lipocalins are involved in a variety of biological processes in the animal organism, such as the transport and storage of poorly soluble substances. For example, lipocalin-1 is present in human lacrimal fluid (Klaver D et al. 2020).

Lipocalins are characterized by a common tertiary structure consisting of an eight-stranded beta-sheet that forms an internal binding pocket. Despite a common tertiary structure, the amino acid sequences of the individual lipocalins are very different. The amino acid identities are often only 20%.

Lipokalins play a role in the regulation of the immune response, including the defence against pathogens in body fluids (e.g. in tear fluid). The amino acid acid densities are only 20%. Various lipokalins are excreted in the urine; they are ascribed a role in social behaviour as they transport pheromones and fragrances.

Another group of lipokalins with a high amino acididicity is an important source of allergens in fur animals and is responsible for cross-allergies between fur animals.

Most animal allergens belong to the protein family of lipokalins. Serum albumin is another family.

There is evidence that a sub-group of lipokalins has a relatively high amino acid identity of 47-67%. They can also cause cross-reactions. Many lipokalins are assigned a role in social maintenance, as they transport pheromones and fragrances.

1. Hilger C et al. (2015) Male-specific submaxillary gland protein, a lipocalin allergen of the golden hamster, differs from the lipocalin allergens of Siberian and Roborovski dwarf hamsters. Int Arch Allergy Immunol 166:30-40.
2. Jensen-Jarolim E et al. (2016) Structural similarities of human and mammalian lipocalins, and their function in innate immunity and allergy. Allergy 71:286-294.

3. Klaver D et al. (2020) Peptides from allergenic lipocalins bind to formyl peptide receptor 3 in human dendritic cells to mediate TH2 immunity. J Allergy Clin Immunol 145:654-665.

4. Rytkönen-Nissinen M et al. (2015) IgE Reactivity of the Dog Lipocalin Allergen Can f 4 and the Development of a Sandwich ELISA for Its Quantification. Allergy Asthma Immunol Res 7:384-392.
5. Roth-Walter Fet al. (2014) Bet v 1 from birch pollen is a lipocalin-like protein acting as allergen only when devoid of iron by promoting Th2 lymphocytes. J Biol Chem 289:17416-17421.