InterPro

Calycins form a large protein superfamily that share similar beta-barrel structures. Calycins can be divided into families that include lipocalins, fatty acid binding proteins, triabin, and thrombin inhibitor [PMID: 11058743]. Of these families, the lipocalin family (IPR002345) is the largest and functionally the most diverse. Lipocalins are extracellular proteins that share several common recognition properties such as ligand binding, receptor binding and the formation of complexes with other macromolecules. Lipocalins include the retinol binding protein, lipocalin allergen, aphrodisin (a sex hormone), alpha-2U-globulin, prostaglandin D synthase, beta-lactoglobulin, bilin-binding protein, and the nitrophorins [PMID: 12432930, PMID: 11058763, PMID: 11058769, PMID: 11058756]. Bacterial hypothetical proteins YodA from Escherichia coli and YwiB from Bacillus subtilis share a similar calycin beta-barrel structure. Part of the YodA hypothetical protein has a calycin-like structure [PMID: 12909634].