发信人: royluo ( 罗马情结), 信区: Biology
标 题: Re: O-link glycosylation
发信站: The unknown SPACE (Fri Jul 25 00:26:46 2003), 站内信件


My lab happens to study one important type of O-glycosylation.
O-glycosylations are carbohydrates linked through hydroxyl groups of
serine or threonine of the protein. There are different types of
O-glycosylations. They have different functions.
(1)O-GalNAc(mucin type)
Originally, O-glycosylation only refers to this type. This type
of glycosylation has usually extended chains(but less branched than
N-glycans). The first carbohydrate moiety linking to the protein is
N-acetylgalactosamine (GalNAc). Protein bearing this type O-glycans
are secreted or cell surface proteins(also called mucin). Mucins
remain at the surface of epithelial cells. Because mucins tend to get
entangled with each other through disulfide bonds and trap a lot of
water ions through O-glycans. So it actually provides protection to
the epithelial cells.O-GalNAc type also has a role in ABO blood type
antigen formation.
There is no good way to precisely predict the sites with O-
GalNAc. But there is a website that may be helpful for predictions
http://www.cbs.dtu.dk/services/NetOGlyc/

(2)O-GlcNAc
This type is very interesting. It dynamically modifies many
cytoplasmic and nucleus protein, contrary to the previous belief
that glycosylation only occurs to secreted or membrane protein.
In this type of glycosylated protein, a single N-acetylglucosamine
(GlcNAc) is added to the hydroxyl group of serine or threonine.
Examples are like p53 , c-myc, RNA polymerase II.
It is believed that this type of glycosylation competes with
phosphorylation and therefore regulates many nucleus protein
function. The following website can be used to predict the site.
http://www.cbs.dtu.dk/services/YinOYang/
BTW: this type of modification is notoriously difficult to
study because of instability.

(3)O-Fucose and O-glucose
I am working on this type, :-)
These two types of modifications were originally found on EGF
repeats on many cell surface protein, like Notch. We don't know
too much about the function of O-glucose. But for O-fucose, we
already know it is essential for Notch signalling. K/O mice displays
Notch K/O phenotype. Another big deal is fringe, an GlcNAc transferase
adding a GlcNAc to the fucose moiety. Fringe is known to play a
role in formation of somite. You can search a lot of nature, science,
cell paper about this protein.
According to experiences, a consensus sequence is suggested to
predict O-fucose modification. But it is not perfect yet.

Not all of the above types have very mature assay methods.
Assays for N-glycan are absolutely much more developed.
The commercially available O-glycosidase is only for
O-GalNAc. It can be used as a marker to confirm your
target protein actually passing through Golgi. Sialic
acid modification only happens in trans Golgi apparatus,
so Sialic acid glycosidase can also be used as a marker
for trans-Golgi.


Finally, for more interest, please go to Pubmed's bookshelf.
"Essentials of glycobiology" is collected. This is an amazing
textbook for glycobiology.
http://www.ncbi.nlm.nih.gov:80/books/bv.fcgi?call=bv.View..ShowTOC&rid
=glyco.TOC&depth=2

【 在 vanLoon (房龙) 的大作中提到: 】
: 请问这种类型的protein主要是用于什么的?glycosylation位置在什么地方?
: secreted? 另外,用kit分析成分跟N-link的技术相比成熟吗?俺看到用了
: O-endoglycosidase和sialic glycosidase的.
: 多谢了.


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