Bovine serum albumin explained

albumin
Organism:	Bos taurus (domestic cow)
Taxid:	9913
Symbol:	ALB
Entrezgene:	280717
Homologene:	105925
Refseqmrna:	NM_180992
Refseqprotein:	NP_851335
Uniprot:	P02769
Chromosome:	6
Entrezchromosome:	NC_007304
Genloc Start:	91543999
Genloc End:	91567876

Bovine serum albumin (BSA or "Fraction V") is a serum albumin protein derived from cows. It is often used as a protein concentration standard in lab experiments.

The nickname "Fraction V" refers to albumin being the fifth fraction of the original Edwin Cohn purification methodology that made use of differential solubility characteristics of plasma proteins. By manipulating solvent concentrations, pH, salt levels, and temperature, Cohn was able to pull out successive "fractions" of blood plasma. The process was first commercialized with human albumin for medical use and later adopted for production of BSA.

Properties

The full-length BSA precursor polypeptide is 607 amino acids (AAs) in length. An N-terminal 18-residue signal peptide is cut off from the precursor protein upon secretion, hence the initial protein product contains 589 amino acid residues. An additional six amino acids are cleaved to yield the mature BSA protein that contains 583 amino acids.^[1]

BSA has three homologous but structurally different domains. The domains, named I, II, and III, are broken down into two sub-domains, A and B.^[1]

Peptide	Position	Length (AAs)	MW Da
Full length precursor	1 – 607	607	69,324
	1 –  18	18	2,107
Propeptide	19 –  24	6	478
Mature protein	25 – 607	583	66,463

Physical properties of BSA:

• Number of amino acid residues: 583
• Molecular weight: 66,463 Da (= 66.5 kDa)
• isoelectric point in water at 25 °C: 4.7^[2]
• Extinction coefficient of 43,824 M⁻¹cm⁻¹ at 279 nm^[3]
• Dimensions: 140 × 40 × 40 Å (prolate ellipsoid where a = b < c)^[4]
• pH of 1% Solution: 5.2-7 ^{[5] [6]}
• Optical Rotation: [α]₂₅₉: -61°; [α]₂₆₄: -63°
• Stokes Radius (r_s): 3.48 nm^[7]
• Sedimentation constant, S_20,W × 10¹³: 4.5 (monomer), 6.7 (dimer)
• Diffusion constant, D_20,W × 10⁻⁷ cm²/s: 5.9
• Partial specific volume, V₂₀: 0.733
• Intrinsic viscosity, η: 0.0413
• Frictional ratio, f/f0: 1.30
• Refractive index increment (578 nm) × 10⁻³: 1.90
• Optical absorbance, A^279 nm_1 g/L: 0.667
• ε₂₈₀ = 43.824 mM⁻¹ cm^{−1 [8]}
• Mean residue rotation, [m']₂₃₃: 8443
• Mean residue ellipticity: 21.1 [θ]_209 nm; 20.1 [θ]_222 nm
• Estimated a-helix, %: 54
• Estimated b-form, %: 18

Function

BSA, like other serum albumins, is critical in providing oncotic pressure within capillaries, transporting fatty acids, bilirubin, minerals and hormones, and functioning as both an anticoagulant and an antioxidant.^[9] There are approximately 6 different long chain fatty acid binding sites on the protein, the three strongest of which are located one per each domain. BSA can also bind other substances such as salicylate, sulfonamides, bilirubin, and other drugs, which bind to “site 1” in subdomain IIA, while tryptophan, thyroxine, octanoate and other drugs that are aromatic in nature bind to “site 2” in subdomain IIIA.^[10]

Applications

BSA is often used a model for other serum albumin proteins, especially human serum albumin, to which it is 76% structurally homologous.^[11]

BSA has numerous biochemical applications including ELISAs (Enzyme-Linked Immunosorbent Assay), immunoblots, and immunohistochemistry. Because BSA is a small, stable, moderately non-reactive protein, it is often used as a blocker in immunohistochemistry.^[12] During immunohistochemistry, which is the process that uses antibodies to identify antigens in cells, tissue sections are often incubated with BSA blockers to bind nonspecific binding sites.^{[13] [14]} This binding of BSA to nonspecific binding sites increases the chance that the antibodies will bind only to the antigens of interest.^[15] The BSA blocker improves sensitivity by decreasing background noise as the sites are covered with the moderately non-reactive protein.^{[16] [17]} During this process, minimization of nonspecific binding of antibodies is essential in order to acquire the highest signal to noise ratio. BSA is also used as a nutrient in cell and microbial culture. In restriction digests, BSA is used to stabilize some enzymes during the digestion of DNA and to prevent adhesion of the enzyme to reaction tubes, pipette tips, and other vessels.^[18] This protein does not affect other enzymes that do not need it for stabilization. BSA is also commonly used to determine the quantity of other proteins, by comparing an unknown quantity of protein to known amounts of BSA (see Bradford protein assay). BSA is used because of its ability to increase signal in assays, its lack of effect in many biochemical reactions, and its low cost, since large quantities of it can be readily purified from bovine blood, a byproduct of the cattle industry. Another use for BSA is that it can be used to temporarily isolate substances that are blocking the activity of the enzyme that is needed, thus impeding polymerase chain reaction (PCR).^[19] BSA has been widely used as a template to synthesize nanostructures ^[20] and determining the toxic or beneficial effects of metal ions and their complexes.^[21]

BSA is also the main constituent of fetal bovine serum, a common cell culture medium.

See also

• Acceptable daily intake
• Protein allergy
• Human serum albumin
• Serum albumin

Further reading

• Hirayama K, Akashi S, Furuya M, Fukuhara K . Rapid confirmation and revision of the primary structure of bovine serum albumin by ESIMS and Frit-FAB LC/MS . Biochemical and Biophysical Research Communications . 173 . 2 . 639–646 . December 1990 . 2260975 . 10.1016/S0006-291X(05)80083-X .
• Zhang M, Desai T, Ferrari M . Proteins and cells on PEG immobilized silicon surfaces . Biomaterials . 19 . 10 . 953–960 . May 1998 . 9690837 . 10.1016/S0142-9612(98)00026-X .
• Web site: Bovine Serum Albumin (7 % Solution) . Wise SA, Watters RL . 2010-06-30 . pdf . Certificate of Analysis . United States National Institute of Standards & Technology . 2011-12-22 .

Notes and References

1. Majorek KA, Porebski PJ, Dayal A, Zimmerman MD, Jablonska K, Stewart AJ, Chruszcz M, Minor W . 6 . Structural and immunologic characterization of bovine, horse, and rabbit serum albumins . Molecular Immunology . 52 . 3–4 . 174–182 . October 2012 . 22677715 . 3401331 . 10.1016/j.molimm.2012.05.011 .
2. Ge S, Kojio K, Takahara A, Kajiyama T . Bovine serum albumin adsorption onto immobilized organotrichlorosilane surface: influence of the phase separation on protein adsorption patterns . Journal of Biomaterials Science. Polymer Edition . 9 . 2 . 131–150 . 1998 . 9493841 . 10.1163/156856298x00479 .
3. Book: Putman FW . Peters T . The Plasma Proteins . 1975 . Academic Press . 133–181.
4. Wright AK, Thompson MR . Hydrodynamic structure of bovine serum albumin determined by transient electric birefringence . Biophysical Journal . 15 . 2 Pt 1 . 137–141 . February 1975 . 1167468 . 1334600 . 10.1016/S0006-3495(75)85797-3 . 1975BpJ....15..137W .
5. Book: Putnam FW . The Plasma Proteins: Structure, Function and Genetic Control . 2nd . 1 . 1975 . Academic Press . New York . 141, 147 . B007ESU1JQ .
6. Web site: Albumin from bovine serum. Sigma-Aldrich. 5 July 2013. 8 October 2013. https://web.archive.org/web/20131008011800/http://www.sigmaaldrich.com/etc/medialib/docs/Sigma/Product_Information_Sheet/b4287pis.Par.0001.File.tmp/b4287pis.pdf. dead.
7. Axelsson I . Characterization of proteins and other macromolecules by agarose gel chromatography . Journal of Chromatography A . May 1978 . 152 . 1 . 21–32 . 10.1016/S0021-9673(00)85330-3 .
8. Web site: TECH TIP #6 Extinction Coefficients . Thermo Fisher Scientific . 29 April 2021.
9. Chen CB, Hammo B, Barry J, Radhakrishnan K . Overview of Albumin Physiology and its Role in Pediatric Diseases . Current Gastroenterology Reports . 23 . 8 . 11 . July 2021 . 34213692 . 10.1007/s11894-021-00813-6 .
10. Book: Peters T . All about albumin : biochemistry, genetics, and medical applications . 1996 . Academic Press . 978-0-12-552110-9 . San Diego . 162129148.
11. Topală T, Bodoki A, Oprean L, Oprean R . Bovine Serum Albumin Interactions with Metal Complexes . Clujul Medical . 87 . 4 . 215–219 . 2014-11-12 . 26528027 . 4620676 . 10.15386/cjmed-357 .
12. Web site: Serum Albumins and Allergies. October 2013. Structural Biology Knowledgebase. National Institute of General Medical Sciences of the National Institutes of Health. 2017-03-29. 2021-10-23. https://web.archive.org/web/20211023192302/http://sbkb.org/fs/serum-albumins-and-allergies. dead.
13. Web site: What Is Immunohistochemistry (IHC) . Immunohistochemistry. Sino Biological Inc..
14. Farwell AP, Dubord-Tomasetti SA . Thyroid hormone regulates the expression of laminin in the developing rat cerebellum . Endocrinology . 140 . 9 . 4221–4227 . September 1999 . 10465295 . 10.1210/endo.140.9.7007 . free .
15. Web site: Tips for Reducing ELISA Background . Biocompare. Compare Networks. October 8, 2012.
16. Web site: How Blocking Works in Immunocytochemical Analysis with Serum or BSA. Ouellet M . December 24, 2006. MadSci Network: Biochemistry. MadSci Network.
17. Web site: Blocker™ BSA (10X) in PBS. Thermo Fisher Scientific. Thermo Fisher Scientific Inc.. https://web.archive.org/web/20170330084559/https://www.thermofisher.com/order/catalog/product/37525. 2017-03-30. dead.
18. Web site: BSA FAQ . Invitrogen. 19 January 2012. https://web.archive.org/web/20111228204619/http://www.neb.com/nebecomm/products/faqproductB9001.asp#572. 2011-12-28. dead.
19. Kreader CA . Relief of amplification inhibition in PCR with bovine serum albumin or T4 gene 32 protein . Applied and Environmental Microbiology . 62 . 3 . 1102–1106 . March 1996 . 8975603 . 167874 . 10.1128/aem.62.3.1102-1106.1996 . 1996ApEnM..62.1102K .
20. Rahmani T, Hajian A, Afkhami A, Bagheri H . A novel and high performance enzyme-less sensing layer for electrochemical detection of methyl parathion based on BSA templated Au–Ag bimetallic nanoclusters. . New Journal of Chemistry . 2018 . 42 . 9 . 7213–22 . 10.1039/C8NJ00425K .
21. Zavalishin MN, Pimenov OA, Belov KV, Khodov IA, Gamov GA . November 2023 . Chemical equilibria in aqueous solutions of H[AuCl4] and bovine or human serum albumin . Journal of Molecular Liquids . en . 389 . 122914 . 10.1016/j.molliq.2023.122914.