User:Rjdodger/sandbox: Difference between revisions
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==Structure== |
==Structure== |
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There are three different forms of galectin structure, dimeric, tandem or chimera. Dimeric galectins, also called prototypical galectins, are homodimers of two identical galectin subunits that have associated with one another. The galectins that fall under this category are galectin-1, -2, -5, -7, -10, -11, -13 and - |
There are three different forms of galectin structure, dimeric, tandem or chimera. Dimeric galectins, also called prototypical galectins, are homodimers of two identical galectin subunits that have associated with one another. The galectins that fall under this category are galectin-1, -2, -5, -7, -10, -11, -13, -14 and -15. Tandem galectins contained at least two distinct carbohydrate recognition domains within one polypeptide. The CRDs are linked with a small peptide domain. Tandem galectins include galectin-4, -5, -8, -9 and -12. The final galectin is galectin-3 which is the only galectin found in the chimera category in vertebrates. Galectin-3 has one CRD and a long non-lectin domain. Galectin-3 can exist in monomeric form or can associate via the non-lectin domain into multivalent complexes <ref name="Liu 2010"> |
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{{Cite journal | author=Liu F| title=Galectins: Regulators of acute and chronic inflammation | journal=[[Annals of the New York Academy of Sciences]] | volume=1183 | year=2010 | pages=158-182 | doi=10.1111/j.1749-6632.2009.05131.x |
{{Cite journal | author=Liu F| title=Galectins: Regulators of acute and chronic inflammation | journal=[[Annals of the New York Academy of Sciences]] | volume=1183 | year=2010 | pages=158-182 | doi=10.1111/j.1749-6632.2009.05131.x}} |
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</ref>. This is concentration dependent. |
</ref>. This is concentration dependent. |
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Many isoforms of galectins have been found due to different [[RNA splicing|splicing]] variants. For example, Galectin-8 has seven different [[messenger RNA|mRNAs]] encoding for both tandem and dimeric forms. Which type of galectin-8 is expressed is dependent on the tissue.<ref name=" |
Many isoforms of galectins have been found due to different [[RNA splicing|splicing]] variants. For example, Galectin-8 has seven different [[messenger RNA|mRNAs]] encoding for both tandem and dimeric forms. Which type of galectin-8 is expressed is dependent on the tissue.<ref name="Cummings book"> |
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{{cite book |last=Varki |first=A |coauthors=RD Cummings, F Liu et al. |title=Essentials of Glycobiology |edition=2nd |chapter=chapter 33: Galectins |url=http://www.ncbi.nlm.nih.gov/books/NBK1908/ |year=2009 |publisher=Cold Spring Harbour (NY) |isbn=9780879697709}} |
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</ref> |
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Galectin-9 has three different isoforms which differ in the length of the linker region.<ref name="Cummings book"> </ref> |
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===Ligand Binding=== |
===Ligand Binding=== |
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===Cellular distribution=== |
===Cellular distribution=== |
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Galectins are unique to other lectins because they do not contain any bound sugars of their own. They are soluble proteins that have no signal peptide or membrane binding domain. They are found in the cytosol, nucleus, in the extracellular matrix and extracellularly outside the cell - this is unlike other lectins which are all membrane bound. |
Galectins are unique to other lectins because they do not contain any bound sugars of their own. They are soluble proteins that have no signal peptide or membrane binding domain. They are found in the cytosol, nucleus, in the extracellular matrix and extracellularly outside the cell - this is unlike other lectins which are all membrane bound. |
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Galectin-1 is highly expresed in the thymus by immune cells including [[T helper cell|Th-1]] cells. |
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! Galectin !! Cellular distribution !! Function !! Implication in disease |
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| Galectin-1 || Secreted by immune cells either in the thymus highly expressed by [[T helper cell|Th-1]] cells or by stromal cells surrounding [[B cells]] || || Can enhance HIV infection |
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| Galectin-2 || Example || Example |
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| Galectin-3 || Example || Example |
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| Galectin-4 || Example || Example |
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| Galectin-5 || Example || Example |
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| Galectin-6 || Example || Example |
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| Galectin-7 || Example || Example |
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| Galectin-8 || Example || Example |
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| Galectin-9 || Example || Example |
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| Galectin-10 || Example || Example |
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| Galectin-11 || Example || Example |
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| Galectin-12 || Example || Example |
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| Galectin-13 || Example || Example |
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| Galectin-14 || Example || Example |
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| Galectin-15 || Example || Example |
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===Physiological roles=== |
===Physiological roles=== |
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Revision as of 16:30, 20 March 2013
GALECTINS
Galectins are soluble proteins without membrane binding domains that are found to have intra- and extracellular functions.
Structure
There are three different forms of galectin structure, dimeric, tandem or chimera. Dimeric galectins, also called prototypical galectins, are homodimers of two identical galectin subunits that have associated with one another. The galectins that fall under this category are galectin-1, -2, -5, -7, -10, -11, -13, -14 and -15. Tandem galectins contained at least two distinct carbohydrate recognition domains within one polypeptide. The CRDs are linked with a small peptide domain. Tandem galectins include galectin-4, -5, -8, -9 and -12. The final galectin is galectin-3 which is the only galectin found in the chimera category in vertebrates. Galectin-3 has one CRD and a long non-lectin domain. Galectin-3 can exist in monomeric form or can associate via the non-lectin domain into multivalent complexes [1]. This is concentration dependent. Many isoforms of galectins have been found due to different splicing variants. For example, Galectin-8 has seven different mRNAs encoding for both tandem and dimeric forms. Which type of galectin-8 is expressed is dependent on the tissue.[2] Galectin-9 has three different isoforms which differ in the length of the linker region.[2]
Ligand Binding
The strength of ligand binding is determined by a number of factors. The multivalency of both of ligand and the galectin, the length of the carbohydrate and the mode of presentation of ligand to carbohydrate recognition domain. Different galectins have slightly different binding specificities depending on the tissue in which they are expressed and the function that they possess. For example, galectin-8 has greater affinity to galactose featuring sugars expressed on intregrin of the extracellular matrix. Crystallisation experiments of galectins in complex with β-lactosamine shows that binding arises due to hydrogen bonding interactions from C4 and C6 hydroxyl group of galactose and C3 of N-acetylglucosamine (GlcNAc) to the side chains of amino acids in the protein.
Function
Cellular distribution
Galectins are unique to other lectins because they do not contain any bound sugars of their own. They are soluble proteins that have no signal peptide or membrane binding domain. They are found in the cytosol, nucleus, in the extracellular matrix and extracellularly outside the cell - this is unlike other lectins which are all membrane bound. Galectin-1 is highly expresed in the thymus by immune cells including Th-1 cells.
| Galectin | Cellular distribution | Function | Implication in disease |
|---|---|---|---|
| Galectin-1 | Secreted by immune cells either in the thymus highly expressed by Th-1 cells or by stromal cells surrounding B cells | Can enhance HIV infection | |
| Galectin-2 | Example | Example | |
| Galectin-3 | Example | Example | |
| Galectin-4 | Example | Example | |
| Galectin-5 | Example | Example | |
| Galectin-6 | Example | Example | |
| Galectin-7 | Example | Example | |
| Galectin-8 | Example | Example | |
| Galectin-9 | Example | Example | |
| Galectin-10 | Example | Example | |
| Galectin-11 | Example | Example | |
| Galectin-12 | Example | Example | |
| Galectin-13 | Example | Example | |
| Galectin-14 | Example | Example | |
| Galectin-15 | Example | Example |
Physiological roles
Apoptosis Suppression of T cell receptor activation Adhesion
Galectins and disease
Cancer
Chronic inflammation
HIV
http://www.ncbi.nlm.nih.gov/books/NBK1944/
- ^ Liu F (2010). "Galectins: Regulators of acute and chronic inflammation". Annals of the New York Academy of Sciences. 1183: 158–182. doi:10.1111/j.1749-6632.2009.05131.x.
- ^ a b
Varki, A (2009). "chapter 33: Galectins". Essentials of Glycobiology (2nd ed.). Cold Spring Harbour (NY). ISBN 9780879697709.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help)