Serum albumin

This article is about the family of mammalian albumin proteins. For the human variant, see human serum albumin. For the cow variant, see bovine serum albumin. For the chicken variant, see conalbumin.
Albumin

PDB rendering based on 1e7h.
Available structures
PDB Ortholog search: PDBe, RCSB
Identifiers
Symbols ALB ; ANALBA; FDAH; PRO0883; PRO0903; PRO1341
External IDs OMIM: 103600 MGI: 87991 HomoloGene: 405 ChEMBL: 3253 GeneCards: ALB Gene
RNA expression pattern
More reference expression data
Orthologs
Species Human Mouse
Entrez 213 11657
Ensembl ENSG00000163631 ENSMUSG00000029368
UniProt P02768 P07724
RefSeq (mRNA) NM_000477 NM_009654
RefSeq (protein) NP_000468 NP_033784
Location (UCSC) Chr 4:
73.4 – 73.42 Mb		 Chr 5:
90.46 – 90.48 Mb
PubMed search

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.[1][2][3] Other mammalian forms, such as bovine serum albumin, are chemically similar.

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. Albumin in the urine usually denotes the presence of kidney disease. Occasionally albumin appears in the urine of normal persons following long standing (postural albuminuria).

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, and thus need less albumin to maintain proper fluid distribution.

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.[3]

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

Main article: Albumin

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.[4]

Serum albumin family

Structure of human serum albumin.[5]
Identifiers
Symbol Serum_albumin
Pfam PF00273
Pfam clan CL0282
InterPro IPR014760
SMART SM00103
PROSITE PS51438
SCOP 1ao6
SUPERFAMILY 1ao6

Types

Serum albumin is widely distributed in mammals.

See also

References

  1. ↑ 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.
  2. ↑ Harper ME, Dugaiczyk A (July 1983). "Linkage of the evolutionarily-related serum albumin and alpha-fetoprotein genes within q11-22 of human chromosome 4". Am. J. Hum. Genet. 35 (4): 565–72. PMC 1685723. PMID 6192711.
  3. 1 2 "Entrez Gene: albumin".
  4. ↑ 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 Struct. Biol. 3: 6. doi:10.1186/1472-6807-3-6. PMC 166163. PMID 12846933.
  5. ↑ Sugio S, Kashima A, Mochizuki S, Noda M, Kobayashi K (June 1999). "Crystal structure of human serum albumin at 2.5 A resolution". Protein Eng. 12 (6): 439–46. doi:10.1093/protein/12.6.439. PMID 10388840.

External links

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