Queratán sulfato: Diferenzas entre revisións

--> Keratan sulfates are large, highly hydrated molecules which in joints can act as a cushion to absorb [[shock (mechanics)|mechanical shock]].

 

Like other [[glycosaminoglycan]]s keratan sulfate is a linear [[polymer]] that consists of a repeating [[disaccharide]] unit. Keratan sulfate occurs as a [[proteoglycan]] (PG) in which KS chains are attached to [[cell-surface]] or [[extracellular matrix]] proteins, termed core proteins. KS core proteins include [[Lumican]], [[Keratocan]], [[Mimecan]], [[Fibromodulin]], [[PRELP]], [[Osteoadherin]] and [[Aggrecan]].

 

The monosaccharide [[mannose]] is found within the linkage region of keratan sulfate type I (KSI). Disaccharides within the repeating region of KSII may be [[fucose|fucosylated]] and [[N-Acetylneuraminic acid]] caps the end of all keratan sulfate type II (KSII) chains and up to 70% of KSI type chains.<ref name=funderburgh>{{cite journal | author = Funderburgh JL. | title = Keratan sulfate: structure, biosynthesis, and function | journal = Glycobiology | year=2000 | volume=10 | issue =10 | pages=951–958 | pmid = 11030741 | doi = 10.1093/glycob/10.10.951}}</ref>

 

The designations KSI and KSII were originally assigned on the basis of the tissue type from which the keratan sulfate was isolated. KSI was isolated from [[corneal]] tissue and KSII from [[skeletal]] tissue.<ref>{{cite journal | author = Meyer K, Linker A. ''et al.'' | title = The mucopolysaccharides of bovine cornea | journal = J. Biol. Chem. | date=1 December 1953| volume=205 | issue=2 | pages=611–616 | url= http://www.jbc.org/cgi/reprint/205/2/611 | pmid = 13129238 }}</ref><ref>{{cite journal | author = Meyer K, Hoffman P. and Linker A. | title = Mucopolysaccharides of Costal Cartilage | journal = Science | year=1958 | volume=128 | issue=3329 | pages=896 | url= http://www.sciencemag.org/cgi/reprint/128/3329/896| pmid = 13592269 | doi = 10.1126/science.128.3329.896}}</ref> Minor monosaccharide compositional differences exist between KS extracted from both sources and even KS extracted from the same source. However, major differences occur in the way each KS type is joined to its core protein.<ref>{{cite journal | author = Seno N, Meyer K. ''et al.'' | title = Variations in Keratosulfates | journal = J. Biol. Chem. | date=1 March 1965| volume=240 | pages=1005–1019 | url= http://www.jbc.org/cgi/reprint/240/3/1005 | pmid = 14284693 | issue = 3 }}</ref> The designations KSI and KSII are now based upon these protein linkage differences. KSI is [[Glycans#N-Linked glycans|N-linked]] to specific [[asparagine]] [[amino acid]]s via [[N-Acetylglucosamine|''N''-acetylglucosamine]] and KSII is [[Glycans#O-Linked glycans|O-linked]] to specific [[Serine]] or [[Threonine]] amino acids via [[N-acetyl galactosamine]].<ref>{{cite journal | author = Nieduszynski IA, Huckerby TN. ''et al.'' | title = There are two major types of skeletal keratan sulphates | journal = Biochem. J. | year=1990 | volume=271 | issue=1 | pages=243–245 | pmid = 2222415 | pmc = 1149539}}</ref> The tissue based classification of KS no longer exists as KS types have been shown to be non tissue specific.<ref name=funderburgh/> A third type of KS (KSIII) has also been isolated from [[brain]] tissue that is O-linked to specific serine or threonine amino acids via [[mannose]].<ref>{{cite journal | author = Krusius T, Finne J. ''et al.'' | title = Identification of an O-glycosidic mannose-linked sialylated tetrasaccharide and keratan sulfate oligosaccharides in the chondroitin sulfate proteoglycan of brain | journal = J. Biol. Chem. | date=25 June 1986| volume=261 | issue=18 | pages=8237–8242 | url= http://www.jbc.org/cgi/reprint/261/18/8237 | pmid = 2941416 }}</ref>

 

===KSII===

===KSIII===

 

==Notas==