Lipocalins
Lipocalins are proteins that bind certain molecules and transport them into the cell . They occur in practically all living things and are involved in a number of important physiological processes. Their structure resembles a funnel or chalice . In this funnel, water-insoluble substances can be taken up, which are transported into the cells after closing with a lid-like molecular structure and docking with receptor proteins . The lipocalins include, for example, the retinol-binding proteins (RBP) that transport vitamin A. Other lipocalins, on the other hand, transport odor and taste factors or bind color pigments.
The lipocalins, which belong to the calycine family , consist of around 180 amino acids and are therefore relatively small. Their biochemical and structural properties as well as their function are well characterized and are characterized by the binding of small hydrophobic molecules, the attachment to specific receptors on the cell surface and the formation of complexes with soluble macromolecules . The name, made up of the word components "lίpos" (Greek for fat) and "kάlyks" / "calix" (Greek / Latin for cup), describes the task and structure of the lipocalins.
The artificial anticalins are derived from the lipocalins and recognize a specific target molecule like an antibody . They are possibly of interest in medicine for therapeutic purposes, since they are in principle suitable for similar applications as therapeutic antibodies .
Lipocalins typically have two orthogonally arranged beta sheets that form a coffee filter-like structure. This structure is also called the beta sandwich in bioinformatics . Non-covalently hydrophobic molecules such as lipids , steroids , fragrances , bile acids or retinoic acid derivatives are bound in the filter bag. So far, only the prostaglandin D synthase , which belongs to the lipocalins, is known to also have enzymatic activity.