Description
Albumin is a known carrier of fatty acids (FA). Thus control over specific FA′s for cell culture is important, as different cell lines can differ in their sensitivity to particular fatty acids. Fatty acid-free human serum albumin (HSA) is therefore useful for cell culture studies where specific fatty acid content must be strictly controlled, so that researchers can use particular fatty acids specific to their cell lines. Fatty acid-free albumin also allows for optimal and maximum binding sites for using specific fatty acids in cell culture. The use of FA-free HSA also addresses concerns about endogenous FA′s potentially in non-FA-free HSA.
Chemical Properties
solid
Uses
Albumin from human serum has been used in the preparation of glycated human serum albumin (gHSA) in a glucose solution. It has also been used in the study to estimate the impact of surface nanotopography and chemical composition on blood compatibility.
Uses
This recombinant variant is recommended for use in absorption, distribution, metabolism, and excretion (ADME) pharmacological research; cell culture; drug delivery research; and cryopreservation of cells.
Uses
Used for detection in immunological analyses. Can be used as an immunological challenge to activate basophils via the IgE receptor.
Application
Albumin from human serum has been used in the preparation of glycated human serum albumin (gHSA) in a glucose solution.
It has also been used in the study to estimate the impact of surface
nanotopography and chemical composition on blood compatibility.
Albumin was used to test its effect on the in vitro bactericidal activity of cefditoren against penicillin-resistant Streptococcus pneumonia.
It has been clinically used in serious and often life-threatening
conditions, such as shock and blood loss due to trauma, burns, and
surgery. It was used also to test the effect of non-enzymatic glycation on the unfolding of human serum albumin.
Definition
Human serum albumin is a class of simple proteins found in living human tissue.
General Description
Prepared under non-denaturing conditions by a modification of the Cohn procedure.
Biochem/physiol Actions
Serum albumin functions as a carrier protein for steroids, fatty acids, and thyroid hormones, and is vital in regulating the colloidal osmotic pressures of blood. Albumin is also seen to bind to exogenous substances, particularly drugs (e.g., ibuprofen, warfarin), and strongly influence their pharmacokinetics. Oxidative stress leading to changes in the redox state of albumin has widely varied effects on its physiological function.
Synthesis
The synthesis of human serum albumin (HSA) comprises both in vivo and in vitro pathways. In vivo, HSA is synthesized exclusively by the liver: its mRNA encodes a 609-amino-acid precursor, pre-pro-albumin, which enters the endoplasmic reticulum, where the N-terminal 18-amino-acid signal peptide is rapidly cleaved, followed by removal of the N-terminal basic 6-amino-acid pro-peptide just before secretion, yielding the mature non-glycosylated monomer of 585 amino acids with a molecular mass of about 66.5 kDa; a healthy adult liver synthesizes approximately 13.8 g of albumin per day, accounting for about 25% of total hepatic protein synthesis[1].
In vitro, recombinant HSA was produced in E. coli by cloning the full coding sequence of mature HSA from a human liver cDNA library into expression plasmids such as pXL276 and its derivatives (with the PL promoter replacing the trp promoter); the recombinant protein was mainly produced as insoluble aggregates, which were resolubilized, refolded by 100-fold slow dilution into refolding buffer, and purified by anion-exchange FPLC with an average final yield of about 40% at laboratory scale[2]. To obtain an authentic N-terminus, a fusion strategy was adopted in which the first six residues of phage λcII protein were fused to mature HSA to boost expression; after refolding, the fusion protein was cleaved in vitro with catalytic amounts of trypsin (<1/1000 w/w), releasing a mature recombinant HSA whose unique N-terminal sequence matched native HSA, and the product was indistinguishable from native HSA by amino acid composition, UV absorption spectroscopy, electrophoretic and chromatographic analyses.
Purification Methods
Albumin is purified by dissolving it in conductivity water and passage at 2-4o through two ion-exchange columns, each containing a 2:1 mixture of anionic and cationic resins (Amberlite IR-120, H-form, Amberlite IRA-400, OH -form). This treatment removes ions and lipid impurities. Care is taken to exclude CO2, and the solution is stored at -15o. [M.ller et al. Trans Faraday Soc 57 312 1961.] More complete lipid removal is achieved by lyophilising the de-ionised solution, covering the dried albumin (human serum) with a mixture of 5% glacial acetic acid (v/v) in iso-octane (previously dried with Na2SO4) and allowing it to stand at 0o (without agitation) for upwards of 6hours before decanting and discarding the extraction mixture, washing with iso-octane, re-extracting, and finally washing twice with iso-octane. The purified albumin is dried under vacuum for several hours, then dialyzed against water for 12-24hours at room temperature, lyophilised, and stored at -10oC [Goodman Science 125 1296 1957]. It has been recrystallised in high (35%) and in low (22%) EtOH solutions from Cohn's Fraction V. The high EtOH recrystallisation is as follows: To 1kg of Fraction V albumin paste at -5o is added 300mL of 0.4 M pH (pH 5.5) acetate buffer in 35% EtOH pre-cooled to -10o and 430 mL of 0.1 M NaOAc in 25% EtOH also at -10o. Best results are obtained by adding all of the buffer and about half of the NaOAc and stirring slowly for 1hour. The rest of the NaOAc is added when all the lumps have disintegrated. The mixture is set aside at -5o for several days to crystallise. 35% EtOH (1 L) is then added to dilute the crystalline suspension and lower the ionic strength prior to centrifugation at -5o (yield 80%). The crystals are further dissolved in 1.5 volumes of 15% EtOH/0.02M NaCl at -5o and clarified by filtration through washed, calcined diatomaceous earth. This solution may be recrystallised by re-adjusting to the conditions in the first crystallisation, or it may be recrystallised at 22% EtOH with the aid of a very small amount of decanol (enough to give a final concentration of 0.02%). Note that crystallisation from lower EtOH concentration gave better purification (i.e. by removing globulins and carbohydrates) and producing a more stable product. The low EtOH recrystallisation is as follows: To 1kg of Fraction V at -10o to -15o is added 500mL of 15% EtOH at -5o, stirred slowly until a uniform suspension is formed. To the 15% EtOH (500mL) is added sufficient 0.2M NaHCO3 solution (125-150mL) at 0o to bring the pH (1:10 dilution) to 5.3. Some temperature rise occurs, and care must be taken to keep the temperature < -5o. If the albumin is incompletely dissolved a small amount of H2O is added (100mL at a time at 0o, allowing 15minutes between additions). Undissolved albumin can be easily distinguished from small amounts of undissolved globulins, or as the last albumin dissolves, the appearance of the solution changes from milky white to hazy grey-green in colour. Keep the solution at -5o for 12hours and filter by suspending in 15g of washed fine calcined diatomaceous earth, and filtering using a Büchner funnel precoated with coarser diatomaceous earth. The filtrate may require two or more similar filtrations to give a clear solution. To crystallise the filtrate, add through a capillary pipette, and with careful stirring, 1/100volume of a solution containing10% decanol and 60% EtOH (at -10o), and seed with the needle-type albumin crystals. After 2-3days, crystallisation is complete. The crystals are centrifuged off. These are suspended with gentle mechanical stirring in one-third their weight of 0.005 M NaCl pre-cooled to 0o. With careful stirring, H2O (at 0o) is added slowly in an amount equal to 1.7 times the weight of the crystals. At this stage there is about 7% EtOH, and the temperature cannot be made lower than -2.5o to -1o. Clarify, and collect as above. [Cohn et al. J Am Chem Soc 69 1753 1947.] Human serum albumin has been purified similarly with 25% EtOH and 0.2% decanol. The isoelectric points of bovine and human serum albumins are 5.1 and 4.9, respectively.
References
[1]
Kragh-Hansen, U. (2016). Human Serum Albumin: A Multifunctional Protein. Albumin in Medicine, 1–24.
https://doi.org/10.1007/978-981-10-2116-9_1 [2]
Latta, M., Knapp, M., Sarmientos, P., Bréfort, G., Becquart, J., Guerrier, L., Jung, G., Mayaux, J.-F. (1987). Synthesis and Purification of Mature Human Serum Albumin from E. Coli. Nature Biotechnology, 5(12), 1309–1314.
https://doi.org/10.1038/nbt1287-1309
