About this Research Topic
Lipocalins form an ancestral protein family that are found in all but one kingdoms of life. Stemming from a short array of family members, Lipocalins rapidly evolved through duplication and divergence in the vertebrate genome, giving rise to nineteen different proteins in humans. In spite of a high sequence diversity of homologous Lipocalins, their tertiary structure displays a resilient fold of eight beta-barrels delimiting a binding pocket, where they can accommodate different hydrophobic ligands.
Lipocalin proteins are differentially expressed by tissues originated from the three germ layers, and in most cases are secreted to the extracellular milieu. The binding pocket is a salient feature and transport roles have been assigned to many Lipocalins. However, several family members have been proposed to perform moonlighting functions or rather general ones, such as immune regulation, storage and transport of metabolic products and cell homeostasis.
A close-to-linear accrual of publications mark the knowledge accumulation on Lipocalins since the family foundation in 1985, but an inflection point appears in the literature after 2006, when the last comprehensive review of this protein family was collected. Since then, an explosion of association studies of Lipocalin expression with many human diseases has taken place, ranging from metabolic and endocrine syndromes to cancer, cardiovascular and neurodegenerative/psychiatric conditions. Regardless of this wealth of correlational data, with their understandable practical use as disease biomarkers, we note very few publications on Lipocalin biological function.
In this Research Topic we plan to systematically review in a cooperative manner the literature on vertebrate Lipocalins with a critical assessment of its validity (i.e., discarding confusing data coming from technical or methodologically questionable results). We will strictly focus on their biological function(s) at every organizational level (molecular, cellular, tissues or organ systems), either derived from data of healthy experimental models or from rigorous studies seeking causality in the natural experiments involving pathologies.
The final aim is to distill a list of feasible (either proven or proposed) functions for each family member, which will help the interested reader both, to recognize putatively shared biochemical Lipocalin function(s) as well as variations of those core physiological protein properties. By fulfilling this objective we feel confident that future research on Lipocalins will experience a new inflection point with fast and significant advance in the knowledge of this essential protein family.
Topic Editor Prof. Åkerström is a co-founder of Preelumina Diagnostics AB (Lund, Sweden) and A1M Pharma AB (Lund, Sweden - today Guard Therapeutics International) and holds patents on the medical use of the Lipocalin alpha-1-microglobulin. The other Topic Editors declare no competing interests with regard to the Research Topic subject.
Keywords: Lipocalin, Calycin, Lipid binding protein, Lipid transport
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