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any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes; "a diet high in protein"

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/01/19 11:01:41」(JST)

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A protein isoform is any of several different forms of the same protein. Different forms of a protein may be produced from very closely related gene duplicates—as 'same protein' or 'a protein' makes no sense for highly diverged paralogs that arose from a single ancestral gene that duplicated billions of years ago and subsequently diverged greatly in sequence, structure and functionality—or may arise from the same gene by alternative splicing. In older literature one can also encounter the use of the term isoform to describe alleles of the same gene, but currently the terms refers mostly to paralogous and alternatively spliced transcripts, not alleles.

The discovery of isoforms could explain the small number of protein coding regions genes revealed by the human genome project: different proteins encoded by the same gene could increase the diversity of the proteome. Isoforms at the DNA level are readily characterized by cDNA transcript studies. Many human genes possess confirmed alternative splicing isoforms. It has been estimated that ~100,000 ESTs can be identified in humans.^[1] Isoforms at the protein level can manifest in deletion of whole domains or shorter loops, usually located on the surface of the protein.^[2]

Glycoforms

A glycoform is an isoform of a protein that differs only with respect to the number or type of attached glycan. Glycoproteins often consist of a number of different glycoforms, with alterations in the attached saccharide or oligosaccharide. These modifications may result from differences in biosynthesis during the process of glycosylation, or due to the action of glycosidases or glycosyltransferases. Glycoforms may be detected through detailed chemical analysis of separated glycoforms, but more conveniently detected through differential reaction with lectins, as in lectin affinity chromatography and lectin affinity electrophoresis. Typical examples of glycoproteins consisting of glycoforms are the blood proteins as orosomucoid, antitrypsin, and haptoglobin. An unusual glycoform variation is seen in neuronal cell adhesion molecule, NCAM involving polysialic acids, PSA.***

Examples

G-actin, despite its conserved nature, has varying number of isoforms, at least six in mammals.
Creatine kinase, the presence of which in the blood can be used as an aid in the diagnosis of myocardial infarction, exists in 3 isoforms.
Hyaluronan synthase, the enzyme responsible for the production of hyaluronan, has three isoforms in mammalian cells.
UDP-glucuronosyltransferase, an enzyme superfamily responsible for the detoxification pathway of many drugs, environmental pollutants, and toxic endogenous compounds has 16 known isoforms encoded in the human genome.^[3]
G6PDA, Normal ratio of active isoforms in cells of any tissue is 1:1 shared with G6PDG. This is precisely the normal isoform ratio in Hyperplasia. Only one of these isoforms is found during neoplasia.^[4]

References

^ Brett, D; Pospisil, H; Valcárcel, J; Reich, J; Bork, P (2002). "Alternative splicing and genome complexity". Nature Genetics 30 (1): 29–30. doi:10.1038/ng803. PMID 11743582.
^ Kozlowski, L.; Orlowski, J.; Bujnicki, J. M. (2012). "Structure Prediction for Alternatively Spliced Proteins". Alternative pre-mRNA Splicing. p. 582. doi:10.1002/9783527636778.ch54. ISBN 9783527636778.
^ Barre L, Fournel-Gigleux S, Finel M, Netter P, Magdalou J, Ouzzine M (March 2007). "Substrate specificity of the human UDP-glucuronosyltransferase UGT2B4 and UGT2B7. Identification of a critical aromatic amino acid residue at position 33". FEBS J. 274 (5): 1256–64. doi:10.1111/j.1742-4658.2007.05670.x. PMID 17263731.
^ Pathoma, Fundamentals of Pathology

External links

MeSH entry protein isoforms
Definitions Isoform

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English Journal

Authentication of processed meat products by peptidomic analysis using rapid ambient mass spectrometry.

Montowska M1, Alexander MR2, Tucker GA3, Barrett DA4.
Food chemistry.Food Chem.2015 Nov 15;187:297-304. doi: 10.1016/j.foodchem.2015.04.078. Epub 2015 Apr 24.
We present the application of a novel ambient LESA-MS method for the authentication of processed meat products. A set of 25 species and protein-specific heat stable peptide markers has been detected in processed samples manufactured from beef, pork, horse, chicken and turkey meat. We demonstrate tha
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Functions of plastid protein import and the ubiquitin-proteasome system in plastid development.

Ling Q1, Jarvis P2.
Biochimica et biophysica acta.Biochim Biophys Acta.2015 Sep;1847(9):939-48. doi: 10.1016/j.bbabio.2015.02.017. Epub 2015 Mar 8.
Plastids, such as chloroplasts, are widely distributed endosymbiotic organelles in plants and algae. Apart from their well-known functions in photosynthesis, they have roles in processes as diverse as signal sensing, fruit ripening, and seed development. As most plastid proteins are produced in the
PMID 25762164

Large-scale genetic analysis of chloroplast biogenesis in maize.

Belcher S1, Williams-Carrier R1, Stiffler N1, Barkan A2.
Biochimica et biophysica acta.Biochim Biophys Acta.2015 Sep;1847(9):1004-16. doi: 10.1016/j.bbabio.2015.02.014. Epub 2015 Feb 26.
BACKGROUND: Chloroplast biogenesis involves a collaboration between several thousand nuclear genes and ~100 genes in the chloroplast. Many of the nuclear genes are of cyanobacterial ancestry and continue to perform their ancestral function. However, many others evolved subsequently and comprise a di
PMID 25725436

Japanese Journal

Comparison of the Anti-Prion Mechanism of Four Different Anti-Prion Compounds, Anti-PrP Monoclonal Antibody 44B1, Pentosan Polysulfate, Chlorpromazine, and U18666A, in Prion-Infected Mouse Neuroblastoma Cells

Yamasaki Takeshi,Suzuki Akio,Hasebe Rie,Horiuchi Motohiro
PLoS ONE 9(9), e106516, 2014-09-02
… Molecules that inhibit the formation of an abnormal　isoform of prion protein (PrPSc) in prion-infected　cells are candidate therapeutic agents for prion　diseases. …
NAID 120005476205

Distribution of a Neural Cell-Specific Isoform of Microtubule-Associated Protein 4 in Growth Cones

Matsushima Kazuyuki,松島一幸,Nakagawa Hiroyuki,中川裕之,Kotani Susumu,小谷享
Science Journal of Kanagawa University 25, 1-5, 2014-06-30
… At least five isoforms of microtubule-associated protein 4 (MAP4) are derivedfrom a single gene by alternative mRNA splicing. … We previously reported the predominant localization of a neural cell-specific isoform of MAP4 (MAP4-SP) over the ubiquitously expressed isoform (MAP4-LP) in neuronal growth cones. … The differential localization of the isoform should underlie its unique function in neural cells.Full-length Paper …
NAID 120005521007

Phase separation of myelin sheath in Triton X-114 solution : predominant localization of the 21.5-kDa isoform of myelin basic protein in the lipid raft-associated domain