Serum albumin

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Serum albumin family
PDB 1o9x EBI.jpg
Structure of human serum albumin. [1]
Identifiers
SymbolSerum_albumin
Pfam PF00273
Pfam clan CL0282
InterPro IPR014760
SMART SM00103
PROSITE PS51438
SCOP2 1ao6 / SCOPe / SUPFAM
Available protein structures:
Pfam   structures / ECOD  
PDB RCSB PDB; PDBe; PDBj
PDBsum structure summary
PDB 1ao6 ​, 1bj5 ​, 1bke ​, 1bm0 ​, 1e78 ​, 1e7a ​, 1e7b ​, 1e7c ​, 1e7e ​, 1e7f ​, 1e7g ​, 1e7h ​, 1e7i ​, 1gni ​, 1gnj ​, 1h9z ​, 1ha2 ​, 1hk1 ​, 1hk2 ​, 1hk3 ​, 1hk4 ​, 1hk5 ​, 1j78 ​, 1j7e ​, 1kw2 ​, 1kxp ​, 1lot ​, 1ma9 ​, 1n5u ​, 1o9x ​, 1tf0 ​, 1uor ​, 1ysx ​, 2bx8 ​, 2bxa ​, 2bxb ​, 2bxc ​, 2bxd ​, 2bxe ​, 2bxf ​, 2bxg ​, 2bxh ​, 2bxi ​, 2bxk ​, 2bxl ​, 2bxm ​, 2bxn ​, 2bxo ​, 2bxp ​, 2bxq ​, 2i2z ​, 2i30 ​, 2vdb ​, 2vue ​, 2vuf ​, 3b9l ​, 3b9m ​

Serum albumin, often referred to simply as blood albumin, is an albumin (a type of globular protein) found in vertebrate blood. Human serum albumin is encoded by the ALB gene. [2] [3] [4] Other mammalian forms, such as bovine serum albumin, are chemically similar.

Contents

Serum albumin is produced by the liver, occurs dissolved in blood plasma and is the most abundant blood protein in mammals. Albumin is essential for maintaining the oncotic pressure needed for proper distribution of body fluids between blood vessels and body tissues; without albumin, the high pressure in the blood vessels would force more fluids out into the tissues. It also acts as a plasma carrier by non-specifically binding several hydrophobic steroid hormones and as a transport protein for hemin and fatty acids. Too much or too little circulating serum albumin may be harmful.

Function

Albumin functions primarily as a carrier protein for steroids, fatty acids, and thyroid hormones in the blood and plays a major role in stabilizing extracellular fluid volume by contributing to oncotic pressure (known also as colloid osmotic pressure) of plasma.

Because smaller animals (for example rats) function at a lower blood pressure, they need less oncotic pressure to balance this[ citation needed ], and thus need less albumin to maintain proper fluid distribution.

As an anionic protein, albumin binds readily to calcium in blood serum and contributes greatly to plasma calcium levels. As such, in clinical applications it is necessary to adjust serum total calcium concentration upward or downward if hypoalbuminemia or hyperalbuminemia is present, respectively (measured serum total calcium decreases by 0.8 mg/dL per unit decrease in albumin concentration below 4 g/dL). [5] [6]

Synthesis

Albumin is synthesized in the liver as preproalbumin which has an N-terminal peptide that is removed before the nascent protein is released from the rough endoplasmic reticulum. The product, proalbumin, is in turn cleaved in the Golgi vesicles to produce the secreted albumin. [4]

Properties

Albumin is a globular, water-soluble, un-glycosylated serum protein of approximate molecular weight of 65,000 daltons.

Albumin (when ionized in water at pH 7.4, as found in the body) is negatively charged. The glomerular basement membrane is also negatively charged in the body; some studies suggest that this prevents the filtration of albumin in the urine. According to this theory, that charge plays a major role in the selective exclusion of albumin from the glomerular filtrate. A defect in this property results in nephrotic syndrome leading to albumin loss in the urine. Nephrotic syndrome patients are sometimes given albumin to replace the lost albumin.

Structure

The general structure of albumin is characterized by several long α helices allowing it to maintain a relatively static shape, which is essential for regulating blood pressure.

Serum albumin contains eleven distinct binding domains for hydrophobic compounds. One hemin and six long-chain fatty acids can bind to serum albumin at the same time. [7]

Types

Serum albumin is widely distributed in mammals.

See also

References

  1. ↑ Sugio S, Kashima A, Mochizuki S, Noda M, Kobayashi K (June 1999). "Crystal structure of human serum albumin at 2.5 A resolution". Protein Engineering. 12 (6): 439–46. doi:10.1093/protein/12.6.439. PMID   10388840.
  2. ↑ Hawkins JW, Dugaiczyk A (1982). "The human serum albumin gene: structure of a unique locus". Gene. 19 (1): 55–8. doi:10.1016/0378-1119(82)90188-3. PMID   6292049.
  3. ↑ Harper ME, Dugaiczyk A (July 1983). "Linkage of the evolutionarily-related serum albumin and alpha-fetoprotein genes within q11-22 of human chromosome 4". American Journal of Human Genetics. 35 (4): 565–72. PMC   1685723 . PMID   6192711.
  4. 1 2 "Entrez Gene: albumin". U.S. National Library of Medicine.
  5. ↑ Goyal A, Anastasopoulou C, Ngu M, Singh S (8 May 2022). "Hypocalcemia". StatPearls. StatPearls Publishing LLC. PMID   28613662.
  6. ↑ Holliman K (March 2012). "Diagnosing a disorder with few symptoms". ACP Internist. American College of Physicians. Retrieved 13 June 2022.
  7. ↑ Zunszain PA, Ghuman J, Komatsu T, Tsuchida E, Curry S (July 2003). "Crystal structural analysis of human serum albumin complexed with hemin and fatty acid". BMC Structural Biology. 3: 6. doi: 10.1186/1472-6807-3-6 . PMC   166163 . PMID   12846933.


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