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β-Lactoglobulin

Introduction

β-Lactoglobulin (β-LG)is the major whey protein of ruminant species. Its amino-acid sequence and 3-dimensional structure show that it is a lipocalin, a widely diverse family, most of which bind small hydrophobic ligands and thus may act as specific transporters, as does serum retinol binding protein ^[1].

Dimeric Lactoglobulin molecules exist in the open conformation at basic pH, whereas they exist in the closed conformation at acidic pH, after undergoing Tanford transition around neutral pH. ^{[2] [3] [4]}

Bovine b-lactoglobulin (β-Lg) is a much studied and commercially important whey protein with an as yet undetermined function, although it is of obvious nutritional value. b-Lg binds a variety of ligands and by comparison of the general structures of these molecules together with several competition studies, it appears that there are at least 3 independent binding sites. In the absence of direct crystallographic evidence, a preliminary modelling study reveals that there is an internal cavity which can readily accommodate retinol in a manner similar to the related lipocalin, retinol-binding protein. On the outer surface, a solvent-accessible hydrophobic cleft runs between the 3-turn a-helix that is packed against the outer surface of the b-barrel. This cleft can accommodate fatty acids like palmitate and stearate. ^[5]

β-Lactoglobulin is a small protein, soluble in dilute salt solution as befits a globulin, with 162 amino acid residues (Mr ∼18,400) that fold up into an 8-stranded, antiparallel β-barrel with a 3-turn α-helix on the outer surface and a ninth β-strand flanking the first strand (see Figure 1). It is this strand that forms a significant part of the dimer interface in the bovine and bovine proteins but, while still present in porcine β-LG, is not involved in the formation of the dimer that forms at low pH.

Function:Primary component of whey, it binds retinol and is probably involved in the transport of that molecule.^[6].

Relevant background

class of protein :Belongs to the calycin superfamily. Lipocalin family. overall function of Lipocalin family: The lipocalins are a family of proteins which transport small hydrophobic molecules such as steroids, bilins, retinoids, and lipids. Lipocalins have been associated with many biological processes, among them immune response, pheromone transport, biological prostaglandin synthesis, retinoid binding, and cancer cell interactions.

wikipedia

short description of protein fold: They share limited regions of sequence homology and a common tertiary structure architecture.[2][3][4][5][6] This is an eight stranded antiparallel beta-barrel with a repeated + 1 topology enclosing an internal ligand binding site.[5][4].^[7] Therefore To know more abouts and the related deseases you can follow the link that leads you to the Portal to Swiss-Prot diseases and variants organisms:These proteins are found in gram negative bacteria, vertebrate cells, and invertebrate cells, and in plants.

Lipocalin Proteins

The merlin-1 protein belongs to the band 4.1 superfamily of membrane-cytoskeletal linkers ^[8]. Within this superfamily merlin-1 is closer to ezrin,radixin and moesin (the ERM proteins). ERM proteins link adehrens junctions to the actin cytoskeleton,and are able to remodel adherens junctions during epithelial morphogenesis. They also maintain the organization of apical surfaces on the plasma membrane ^[9].

Structure of β-LG

Overview of Crystalline Structure

βLG consists of 162 amino acid residues (18 kDa), containing two disulfide bonds (Cys 66–Cys 160 and Cys 106–Cys 119) and a free thiol (Cys 121). Structures of βLG have been reported by several groups with X-ray crystallography [19–21] and solution NMR [29,40,41] (Fig. 1A). It is a predominantly β-sheet protein. The β-barrel, or so called calyx, is conical and is made of two β-sheets: the B–D strands and N-terminal half of the A strand (denoted AN) form one sheet, and the E–H strands and C-terminal half of the A strand (denoted AC) form the other (Fig. 1B). On the outer surface of the β-barrel, between the G and H strands, is the 3-turn α-helix. The loops that connect the β-strands at the closed end of the calyx, BC, DE, and FG,are generally quite short, whereas those at the open end, AB, CD, EF, and GH, are significantly longer and more flexible [19]. In the calyx,there is a large central cavity which is surrounded by hydrophobic residues and is accessible to solvent. This cavity provides the principal ligand-binding site. βLG contains two tryptophan residues, Trp 19 on the A strand and Trp 61 on the C strand. The former is buried in the hydrophobic core whereas the latter is exposed to the solvent in the native structure, making them useful probes for monitoring site-specific conformational changes. In addition, studies on the monomer–dimer equilibrium [30,32,42,43] and the reactivity of the thiol group of Cys121 deeply buried between the α-helix and H strand [44–48] revealed other important properties of βLG.

overall description of the structure of the protein: a. oligomeric state b. description of secondary structure c. description of active residues of the protein and where they are on the protein d. description of any ligands in the structure e. methods used to solve the structure : X-ray crystallography, NMR, EM

Molecular mechanism of the Tanford transition

Equilibrium transition Although βLG exists in a native state over a wide range of pH values, it shows slight conformational changes during a change of pH [54]. Among the pH-dependent conformational changes of βLG, the Tanford transition is the most important because it is thought to be related to the function of βLG. Tanford et al. [55] observed a change in optical rotatory dispersion at pH 7.0 representing a certain conformational change. Subsequently, they found that this conformational change is accompanied by a deprotonation of a carboxyl group with an anomalous pKa of 7.5 [20,55].

Subunit structure

Under physiological conditions beta-lactoglobulin exists as an equilibrium mixture of monomeric and dimeric forms. Subcellular location: Secreted. Tissue specificity: Synthesized in mammary gland and secreted in milk. Post-translational modification : Alternate disulfide bonds occur in equal amounts in all variants examined. Allergenic properties:Causes an allergic reaction in human. Is one of the causes of cow's milk allergy. Miscellaneous The B variant sequence is shown.

secondary structure elements

protein fold and how thats important for the function ligands if theres ligands the active site if relevant features of protein that are important for function zoom in on the active site, label the important active site residues, and hughlight those residues in a different color (make it look pretty)

Mechanism of action

how the protein function

include chemical structure of any relevant ligands, inhibitors, or important states in the reaction pathway.

Implications or possible application

describe any uses or application that have been made of the protein

References

at least 5

example on how to put content in proteopedia:

Protein unfolding

C-terminal domain^[10].

A pathway of sequential unfolding (and folding) of the native 3D structure S0. SU is the coil. The U–ν links in the intermediate Sν keep their native positions and conformations (they are shown as a solid line against the background of a dotted cloud denoting the globule), whereas the other ν links (shown in dashed line) are unfolded.

Contoh 2

The FERM-tail complex represents an inactive form of the protein in which membrane protein and active binding sites are masked.[11]

and α-helical domains^[12].Conformational changes activate the proteins because they modify the intramolecular contacts, allowing them to bind to their partners. The FERM domain has a fundamental role because it allows ERM proteins to interact with integral proteins of the plasma membrane^[13].

Specificity of contoh domain

Template:STRUCTURE 2q2m As showed in the default scene, the structure 2Q2M has in total 1 Chain. These are represented by 1 sequence-unique entity. The chains A,B and C possess 9 Alpha Helices and 15  Beta Strands  and the chain D has only 9 Alpha Helicesand 14  Beta Strands . You can visualize their .

Structural differences

More precisly,binding of the tail provokes dimerization and unfurling of the F2 motif of the FERM domain.The “closed” complex of merlin-1 is in fact an “open” dimer ^[10]. For more details about the probable quaternary states, see the PDBe page about the structure of 3u8z.

Applications

External Resources

• See: Oncogenes & Tumor Suppressor Genes for Additional examples of oncogenes and tumor suppressor genes.
  
• See: Cancer for Additional Proteins involved in the disease.
  

• Hennigan RF, Moon CA, Parysek LM, Monk KR, Morfini G, Berth S, Brady S, Ratner N. The NF2 tumor suppressor regulates microtubule-based vesicle trafficking via a novel Rac, MLK and p38(SAPK) pathway. Oncogene. 2012 Apr 23. doi: 10.1038/onc.2012.135. PMID:22525268 doi:10.1038/onc.2012.135
• Sun CX, Robb VA, Gutmann DH. Protein 4.1 tumor suppressors: getting a FERM grip on growth regulation. J Cell Sci. 2002 Nov 1;115(Pt 21):3991-4000. PMID:12356905
• Johnson KC, Kissil JL, Fry JL, Jacks T. Cellular transformation by a FERM domain mutant of the Nf2 tumor suppressor gene. Oncogene. 2002 Sep 5;21(39):5990-7. PMID:12203111 doi:10.1038/sj.onc.1205693
• Li Q, Nance MR, Kulikauskas R, Nyberg K, Fehon R, Karplus PA, Bretscher A, Tesmer JJ. Self-masking in an intact ERM-merlin protein: an active role for the central alpha-helical domain. J Mol Biol. 2007 Feb 2;365(5):1446-59. Epub 2006 Oct 26. PMID:17134719 doi:10.1016/j.jmb.2006.10.075
• Surace EI, Haipek CA, Gutmann DH. Effect of merlin phosphorylation on neurofibromatosis 2 (NF2) gene function. Oncogene. 2004 Jan 15;23(2):580-7. PMID:14724586 doi:10.1038/sj.onc.1207142
• Mani T, Hennigan RF, Foster LA, Conrady DG, Herr AB, Ip W. FERM domain phosphoinositide binding targets merlin to the membrane and is essential for its growth-suppressive function. Mol Cell Biol. 2011 May;31(10):1983-96. doi: 10.1128/MCB.00609-10. Epub 2011 Mar , 14. PMID:21402777 doi:10.1128/MCB.00609-10
• Pearson MA, Reczek D, Bretscher A, Karplus PA. Structure of the ERM protein moesin reveals the FERM domain fold masked by an extended actin binding tail domain. Cell. 2000 Apr 28;101(3):259-70. PMID:10847681

References

1. ↑ Kontopidis G, Holt C, Sawyer L. Invited review: beta-lactoglobulin: binding properties, structure, and function. J Dairy Sci. 2004 Apr;87(4):785-96. PMID:15259212 doi:http://dx.doi.org/10.3168/jds.S0022-0302(04)73222-1
2. ↑ Vijayalakshmi L, Krishna R, Sankaranarayanan R, Vijayan M. An asymmetric dimer of beta-lactoglobulin in a low humidity crystal form-Structural changes that accompany partial dehydration and protein action. Proteins. 2007 Oct 11;71(1):241-249. PMID:17932936 doi:10.1002/prot.21695
3. ↑ Sakurai K, Goto Y. Dynamics and mechanism of the Tanford transition of bovine beta-lactoglobulin studied using heteronuclear NMR spectroscopy. J Mol Biol. 2006 Feb 17;356(2):483-96. Epub 2005 Dec 1. PMID:16368109 doi:http://dx.doi.org/10.1016/j.jmb.2005.11.038
4. ↑ Qin BY, Bewley MC, Creamer LK, Baker HM, Baker EN, Jameson GB. Structural basis of the Tanford transition of bovine beta-lactoglobulin. Biochemistry. 1998 Oct 6;37(40):14014-23. PMID:9760236 doi:10.1021/bi981016t
5. ↑ http://www.sciencedirect.com/science/article/pii/S0958694698000211
6. ↑ Kontopidis G, Holt C, Sawyer L. Invited review: beta-lactoglobulin: binding properties, structure, and function. J Dairy Sci. 2004 Apr;87(4):785-96. PMID:15259212 doi:http://dx.doi.org/10.3168/jds.S0022-0302(04)73222-1
7. ↑ Martuza RL, Eldridge R. Neurofibromatosis 2 (bilateral acoustic neurofibromatosis). N Engl J Med. 1988 Mar 17;318(11):684-8. PMID:3125435 doi:http://dx.doi.org/10.1056/NEJM198803173181106
8. ↑ Trofatter JA, MacCollin MM, Rutter JL, Murrell JR, Duyao MP, Parry DM, Eldridge R, Kley N, Menon AG, Pulaski K, et al.. A novel moesin-, ezrin-, radixin-like gene is a candidate for the neurofibromatosis 2 tumor suppressor. Cell. 1993 Nov 19;75(4):826. PMID:8242753
9. ↑ Brault E, Gautreau A, Lamarine M, Callebaut I, Thomas G, Goutebroze L. Normal membrane localization and actin association of the NF2 tumor suppressor protein are dependent on folding of its N-terminal domain. J Cell Sci. 2001 May;114(Pt 10):1901-12. PMID:11329377
10. ↑ ^{10.0 10.1 10.2} Fehon RG, McClatchey AI, Bretscher A. Organizing the cell cortex: the role of ERM proteins. Nat Rev Mol Cell Biol. 2010 Apr;11(4):276-87. doi: 10.1038/nrm2866. PMID:20308985 doi:10.1038/nrm2866
11. ↑ doi: https://dx.doi.org/10.1074/jbc.274.1.170
12. ↑ Yogesha SD, Sharff AJ, Giovannini M, Bricogne G, Izard T. Unfurling of the band 4.1, ezrin, radixin, moesin (FERM) domain of the merlin tumor suppressor. Protein Sci. 2011 Oct 19. doi: 10.1002/pro.751. PMID:22012890 doi:10.1002/pro.751
13. ↑ Bretscher A, Edwards K, Fehon RG. ERM proteins and merlin: integrators at the cell cortex. Nat Rev Mol Cell Biol. 2002 Aug;3(8):586-99. PMID:12154370 doi:10.1038/nrm882

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