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Retinol-binding protein in a calculated membrane-bound state of the protein 1kt6
Symbol Lipocalin
Pfam PF00061
InterPro IPR000566
SCOP 1hms
OPM family 52
OPM protein 1kt6
Available PDB structures:

1qy0A:34-173 1qy1A:34-173 1yp6A:34-173 1znkA:34-173 1zneA:34-173 2a2uD:35-174 1bj7 :29-168 1e5pD:23-163 1e06B:13-153 1gt4A:14-153 1cj5A:32-173 2akqB:32-173 2blg :32-173 1b0o :32-173 1exsA:34-171 1lf7A:48-186 1iw2A:48-186 1jzuA:31-171 1dfvA:48-193 1x89C:48-193 1x71A:48-193 1x8uB:48-193 1epaA:34-174 1epbA:34-174 1fen :21-171 1erb :21-171 1kt5A:21-171 1hbp :21-171 1fel :21-171 1fem :21-171 1kt3A:21-171 1kt4A:21-171 1hbq :21-171 1kt6A:21-171 1kt7A:21-171 1aqb :39-159 1brp :39-189 1jyjA:39-189 1brq :39-189 1jydA:39-189 1rbp :39-189 1iiuA:42-188 1lkeA:38-182 1z24A:24-172 1gkaB:27-168 1s44B:32-171 1obqB:32-171 1i4uB:32-171 1obuA:32-171 1s2pA:32-171 1h91B:32-171 1opbA:6-133 1eiiA:6-133 1b4m :6-133 1opaA:6-133 1kqwA:6-134 1kqxA:6-134 1lpjA:6-134 1crb :6-134 1mx8A:6-134 1gglA:6-133 1xcaB:5-137 3cbsA:5-137 1blr :5-137 2cbsA:5-137 1bm5 :5-137 1cbs :5-137 1cbq :5-137 2cbrA:5-136 1cbiA:5-136 1cbrA:5-136 1ftpA:6-133 1g5wA:6-132 2hmb :6-131 1hmr :6-131 1hms :6-131 1bwyA:6-132 1fdqA:6-131 1fe3A:6-131 1b56 :8-134 1jjjA:8-134 1mf9A:5-132 1o8vA:5-132 1vyfA:5-132 1vygA:5-132 1sa8A:36-131 1ifb :4-131 1ael :4-131 1dc9A:4-131 2ifb :4-131 1icm :4-131 3ifbA:4-131 1kzwA:4-131 1kzxA:4-131 1mdc :4-131 1tvqA:4-125 1mvgA:4-125 1tw4A:4-125 1zryA:4-125 1p6pA:4-125 2f73E:4-127

Lipocalin-like domain
Symbol Lipocalin_2
Pfam PF08212
InterPro IPR013208
OPM family 52
OPM protein 1qwd
Available PDB structures:

1qwdA:34-174 2apd :37-182

The lipocalins are a family of proteins which transport small hydrophobic molecules such as steroids, bilins, retinoids, and lipids. They share limited regions of sequence homology and a common tertiary structure architecture[1][2][3][4][5]. This is an eight stranded antiparallel beta-barrel with a repeated + 1 topology enclosing a internal ligand binding site[4][3].

These proteins are found in gram negative bacteria, vertebrate cells, and invertebrate cells, and in plants. Lipocalins have been associated with many biological processes, among them immune response, pheromone transport, biological prostaglandin synthesis, retinoid binding, and cancer cell interactions.



Immune Response

Lipocalin proteins are involved in inflammation and detoxification processes caused by immune system activation in mammals. They are known respiratory allergens of mice, cats, dogs, horses, and other animals. Examples of lipocalin proteins involved in immune system responses include alpha-1-microglobulin, alpha-1-acid glycoprotein, and c8gamma. Structural information for many immune system influencing lipocalin proteins is available, while their exact role in biological systems is still somewhat unclear. Human allergenic reactions to lipocalins have not been extensively investigated.

Pheromone Transport

The lipocalin family has been connected with the transport of mammalian pheromones due to easily observable protein-pheromone interactions. Lipocalins are comparatively small in size, and are thus less complicated to study as opposed to large, bulky proteins. They can also bind to various ligands for different biological purposes. Lipocalins have been detected as carrier proteins of important pheromones in the nasal mucus of rodents, as well as mouse and rat urine.

Prostaglandin Synthesis

Main article: Prostaglandin

This family of proteins plays a part in the biological system of terminal prostaglandin synthesis.

Retinoid Binding

Retinol, (vitamin A), is an important micronutrient that affects eyesight, cell differentiation, immune system function, bone growth, and tumor suppression. Retinol absorption and metabolism depends on lipocalins that act as binding proteins. Retinyl esters (present in meats) and beta-carotene (present in plants) are the two main sources of retinoids in the diet. After intake, they are converted to retinol, successively metabolized, and finally bound to retinol binding proteins (lipocalins) in the blood plasma.

Cancer Cell Interactions

Because lipocalins are extracellular proteins, their intracellular effects are not obvious, and demand further study. However, lipophilic ligands, present as substituents to the lipocalins, have the ability to enter the cell, where they can act as tumor protease inhibitors. This research suggests another possible route of protein-tumor investigations.


Some of the proteins in this family are allergens. Allergies are hypersensitivity reactions of the immune system to specific substances called allergens (such as pollen, stings, drugs, or food) that, in most people, result in no symptoms. A nomenclature system has been established for antigens (allergens) that cause IgE-mediated atopic allergies in humans [6]. This nomenclature system is defined by a designation that is composed of the first three letters of the genus; a space; the first letter of the species name; a space and an arabic number. In the event that two species names have identical designations, they are discriminated from one another by adding one or more letters (as necessary) to each species designation.

The allergens in this family include allergens with the following designations: Bla g 4, Bos d 2, Bos d 5, Can f 1, Can f 2, Equ c 1 and Equ c 2.


Although lipocalins are a broad family of greatly varied proteins, their three-dimensional structure is a unifying characteristic. Lipocalins have an eight-stranded, antiparallel, symmetrical β-barrel fold, which is in essence a beta sheet which has been rolled into a cylindrical shape. Inside this barrel is located a ligand binding site, which plays an important role in the lipocalin classification as a transport protein. Lipocalins have desirable properties in terms of crystallization ability, molecular size, and commercial availability. Structure determination involves such processes as crystallization and multi-dimensional Nuclear Magnetic Resonance spectroscopy (NMR). Specifically, this NMR technique is known as NOESY (Nuclear Overhauser Effect Spectroscopy), and is used to determine structures of otherwise complex macromolecules such as proteins. If lipocalins are genetically engineered in the attempt to modify their binding properties, they are called Anticalins.

Proteins included in the family

The name 'lipocalin' has been proposed[1] for this protein family, but cytosolic fatty acid binding proteins are also included. The sequences of most members of the family, the core or kernal lipocalins, are characterised by three short conserved stretches of residues, while others, the outlier lipocalin group, share only one or two of these[7][4]. Proteins known to belong to this family include alpha-1-microglobulin (protein HC); alpha-1-acid glycoprotein (orosomucoid)[8]; aphrodisin; apolipoprotein D; beta-lactoglobulin; complement component C8 gamma chain[9]; crustacyanin[10]; epididymal-retinoic acid binding protein (E-RABP)[11]; insectacyanin; odorant-binding protein (OBP); human pregnancy-associated endometrial alpha-2 globulin; probasin (PB), a prostatic protein; prostaglandin D synthase (EC[12]; purpurin; Von Ebner's gland protein (VEGP)[13]; and lizard epididymal secretory protein IV (LESP IV)[14].

Human proteins that contain lipocalin domain



  1. ^ a b Pervaiz S, Brew K (1987). "Homology and structure-function correlations between alpha 1-acid glycoprotein and serum retinol-binding protein and its relatives". FASEB J. 1 (3): 209-214. PMID 3622999.
  2. ^ Nagata A, Igarashi M, Toh H, Urade Y, Hayaishi O (1992). "Structural organization of the gene for prostaglandin D synthase in the rat brain". Proc. Natl. Acad. Sci. U.S.A. 89 (12): 5376-5380. PMID 1608945.
  3. ^ a b Cowan SW, Jones TA, Newcomer ME (1990). "Crystallographic refinement of human serum retinol binding protein at 2A resolution". Proteins 8 (1): 44-61. PMID 2217163.
  4. ^ a b c Flower DR, Attwood TK, North AC (1993). "Structure and sequence relationships in the lipocalins and related proteins". Protein Sci. 2 (5): 753-761. PMID 7684291.
  5. ^ Godovac-Zimmermann J (1988). "The structural motif of beta-lactoglobulin and retinol-binding protein: a basic framework for binding and transport of small hydrophobic molecules?". Trends Biochem. Sci. 13 (2): 64-66. PMID 3238752.
  6. ^ [WHO/IUIS Allergen Nomenclature Subcommittee King T.P., Hoffmann D., Loewenstein H., Marsh D.G., Platts-Mills T.A.E., Thomas W. Bull. World Health Organ. 72:797-806(1994)]
  7. ^ Flower DR, Attwood TK, North AC (1991). "Mouse oncogene protein 24p3 is a member of the lipocalin protein family". Biochem. Biophys. Res. Commun. 180 (1): 69-74. PMID 1834059.
  8. ^ Wilting J, Kremer JM, Janssen LH (1988). "Drug binding to human alpha-1-acid glycoprotein in health and disease". Pharmacol. Rev. 40 (1): 1-47. PMID 3064105.
  9. ^ Peitsch MC, Tschopp J, Jenne DE, Haefliger JA (1991). "Structural and functional characterization of complement C8 gamma, a member of the lipocalin protein family". Mol. Immunol. 28 (1): 123-131. PMID 1707134.
  10. ^ Keen JN, Caceres I, Eliopoulos EE, Zagalsky PF, Findlay JB (1991). "Complete sequence and model for the A2 subunit of the carotenoid pigment complex, crustacyanin". Eur. J. Biochem. 197 (2): 407-417. PMID 2026162.
  11. ^ Newcomer ME (1993). "Structure of the epididymal retinoic acid binding protein at 2.1 A resolution". Structure 1 (1): 7-18. PMID 8069623.
  12. ^ Boguski MS, Peitsch MC (1991). "The first lipocalin with enzymatic activity". Trends Biochem. Sci. 16 (10): 363-363. PMID 1723819.
  13. ^ Kock K, Ahlers C, Schmale H (1994). "Structural organization of the genes for rat von Ebner's gland proteins 1 and 2 reveals their close relationship to lipocalins". Eur. J. Biochem. 221 (3): 905-916. PMID 7514123.
  14. ^ Morel L, Depeiges A, Dufaure JP (1993). "LESP, an androgen-regulated lizard epididymal secretory protein family identified as a new member of the lipocalin superfamily". J. Biol. Chem. 268 (14): 10274-10281. PMID 8486691.

Further reading

  • The Lipocalins: A Review. The Edward Jenner Institute for Vaccine Research.
  • Virtanen, Tuomas et al. "Important Animal Allergens Are Lipocalin Proteins: Why Are They Allergenic?" Department of Clinical Microbiology; University of Kuopio. International Archives of Allergy and Immunology, 1999.
  • Bratt, T. "Lipocalins and Cancer". M&E Biotech. PubMed; 10/18/2000.
  • Charron, Jean-Benoit Frenette et al. "Identification, Expression, and Evolutionary Analyses of Plant Lipocalins" Département des Sciences Biologiques, Université du Québec à Montréal. 10/04/2005.
  • Novotny, M.V. et al. "Pheromones, binding proteins and receptor responses in rodents" Institute for Pheromone Research, University of Indiana, Bloomington. Biochemical Society Transactions, 2003.
  • Diwan, J. "Review: Protein Structure". Rensselaer Polytechnic Institute. 2003.

See also

Retinol binding protein

This article includes text from the public domain Pfam and InterPro IPR000566

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lipocalin". A list of authors is available in Wikipedia.
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