β-Lactoglobulin is the major whey protein of cow and sheep's milk ~3 g/l, and is also present in many other mammalian species; a notable exception being humans Its structure, properties and biological role have been reviewed many times
Structure and role
Unlike the other main whey protein, α-lactalbumin, no clear function has been identified for β-lactoglobulin β-lactoglobulin is a lipocalin protein, and can bind many hydrophobic molecules, suggesting a role in their transport β-lactoglobulin has also been shown to be able to bind iron via siderophores and thus might have a role in combating pathogens A homologue of β-lactoglobulin is lacking in human breast milk
Several genetic variants have been identified, the main ones in the cow being labelled A and B Because of its abundance and ease of purification, it has been subjected to a wide range of biophysical studies Its structure has been determined several times by X-ray crystallography and NMR β-lactoglobulin is of direct interest to the food industry since its properties can variously be advantageous or disadvantageous in dairy products and processing
Bovine β-lactoglobulin is a relatively small protein of 162 residues, with an 184 kDa In physiological conditions it is predominantly dimeric, but dissociates to a monomer below about pH 3, preserving its native state as determined by using NMR Conversely, β-lactoglobulin also occurs in tetrameric, octameric and other multimeric aggregation forms under a variety of natural conditions
β-Lactoglobulin solutions form gels in various conditions, when the native structure is sufficiently destabilised to allow aggregation Under prolonged heating at low pH and low ionic strength, a transparent `fine-stranded' gel is formed, in which the protein molecules assemble into long stiff fibres
β-Lactoglobulin is the main component of milk skin, coagulating and denaturing when the milk boils Once denatured, the β-Lactoglobulin forms a thin gelatinous film on the surface of the milk
Folding intermediates for this protein can be studied using light spectroscopy and denaturant Such experiments show an unusual but important intermediate composed purely of alpha helices, despite the fact that the native structure is beta sheet Evolution has probably selected for the helical intermediate to avoid aggregation during the folding process
As milk is a known allergen, manufacturers need to prove the presence or absence of β-lactoglobulin to ensure their labelling satisfies the requirements of the EC Directive Food testing laboratories can use enzyme linked immunosorbent assay methods to identify and quantify β-lactoglobulin in food products
Laboratory polymerization of β-lactoglobulin by microbial transglutaminase reduces its allergenicity in children and adults with an IgE-mediated cow’s milk allergy
- ^ Hambling, S G, A S McAlpine, and L Sawyer 1992 Advanced Dairy Chemistry: 1 Proteins, chapter: Beta-lactoglobulin Elsevier Applied Science, 141–190
- ^ Sawyer, L, and G Kontopidis 2000 The core lipocalin, bovine beta-lactoglobulin Biochim Biophys Acta 1482:136–48
- ^ Kontopidis, G, C Holt, and L Sawyer 2004 Invited review: beta-lactoglobulin: binding properties, structure, and function J Dairy Sci 87:785–96
- ^ Roth-Walter, Franziska; Pacios, Luis F; Gomez-Casado, Cristina; Hofstetter, Gerlinde; Roth, Georg A; Singer, Josef; Diaz-Perales, Araceli; Jensen-Jarolim, Erika 2014-01-01 "The major cow milk allergen Bos d 5 manipulates T-helper cells depending on its load with siderophore-bound iron" PLOS ONE 9 8: e104803 doi:101371/journalpone0104803 ISSN 1932-6203 PMC 4130594 PMID 25117976
- ^ Fiocchi, Alessandro; Brozek, Jan; Schünemann, Holger; Bahna, Sami L; von Berg, Andrea; Beyer, Kirsten; Bozzola, Martin; Bradsher, Julia; Compalati, Enrico 2010-04-01 "World Allergy Organization WAO Diagnosis and Rationale for Action against Cow's Milk Allergy DRACMA Guidelines" The World Allergy Organization Journal 3 4: 57–161 doi:101097/WOX0b013e3181defeb9 ISSN 1939-4551 PMC 3488907 PMID 23268426
- ^ http://wwwpdborg entry 3BLG
- ^ Jost, R 1993 Functional characteristics of dairy proteins Trends in Food Science & Technology 4:283–288
- ^ Uhrinova, S, M H Smith, G B Jameson, D Uhrin, L Sawyer, and P N Barlow 2000 Structural changes accompanying pH-induced dissociation of the beta-lactoglobulin dimer Biochemistry 39:3565–74
- ^ Timasheff, SN, and Townend, R 1964 Structure of the β-Lactoglobulin Tetramer Nature 203:517-519
- ^ Gottschalk, M, Nilsson, H, Roos, H, and Halle, B 2003 Protein self-association in solution: The bovine β -lactoglobulin dimer and octamer Protein Sci 12:2404–2411
- ^ Rizzuti, B, Zappone, B, De Santo, MP, Guzzi, R 2010 Native β-Lactoglobulin Self-Assembles into a Hexagonal Columnar Phase on a Solid Surface, Langmuir 26:1090–1095
- ^ Bromley, E H C, M R H Krebs, and A M Donald 2005 Aggregation across the length scales in beta-lactoglobulin Faraday Discussions 128:13–27
- ^ Kuwajima K, Yamaya H & Sugai S 1996 The Burst-phase Intermediate in the Refolding of beta-Lactoglobulin Studied by Stopped-flow Circular Dichroism and Absorption Spectroscopy Journal of Molecular Biology, 264:806-822
- ^ listed in Annex IIIa of Directive 2000/13/EC
- ^ Olivier CE, Lima RP, Pinto DG, Santos RA, Silva GK, Lorena SL, Villas-Boas MB, Netto FM, Zollner Rde L: In search of a tolerance-induction strategy for cow's milk allergies: significant reduction of beta-lactoglobulin allergenicity via transglutaminase/cysteine polymerization Clinics Sao Paulo 2012, 6710:1171-1179PDF
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