蛋白質(zhì)四種糖基化：O位糖基化、N位糖基化、C位甘露糖化

    在真核動(dòng)物細(xì)胞中有 20 多種蛋白質(zhì)翻譯后修飾過(guò)程, 常見(jiàn)的有泛素化、磷酸化、糖基化、酯基化、甲基化和乙?；?。mRNA 被翻譯成蛋白質(zhì)后, 對(duì)蛋白質(zhì)上個(gè)別氨基酸殘基進(jìn)行共價(jià)修飾的過(guò)程,即蛋白質(zhì)翻譯后修飾過(guò)程。尤為重要，它使蛋白質(zhì)的結(jié)構(gòu)更為復(fù)雜，功能更為完善，調(diào)節(jié)更為精細(xì)，作用更為專一。

(There are more than 20 post-translation modifications of protein in Eukaryotic cells,the most common areUbiquitination, Phosphorylation, glycosylation,esterification, methylation and acetylation, etc. Post-translational protein modificationthe,which entails the covalent addition of sugar moieties to specific amino acids after mRNA be translated to protein.it play important roles in organisms, which make structures of proteins more complicated ,functions more consummate,the regulation more fine and role more specific.)

 

 

一、糖基化定義

糖基化是在酶的控制下，蛋白質(zhì)或脂質(zhì)附加上糖類的過(guò)程，發(fā)生于內(nèi)質(zhì)網(wǎng)。在糖基轉(zhuǎn)移酶作用下將糖轉(zhuǎn)移至蛋白質(zhì)，和蛋白質(zhì)上的氨基酸殘基形成糖苷鍵。蛋白質(zhì)經(jīng)過(guò)糖基化作用，形成糖蛋白。糖基化是對(duì)蛋白的重要的修飾作用，有調(diào)節(jié)蛋白質(zhì)功能作用。

一、Definition of glycosylation

(Glycosylation,under the control of enzymes,the attachment of sugar moieties to proteins and lipids in the endoplasmic reticulum. Glycan portion is transfered to the protein by Glycosyltransferases,and form glycoside bonds with amino acid residues in proteins. Protein become glycoproteins by Glycosylation. Protein glycosylation has multiple functions in the cell.)

 

二、 分類

蛋白質(zhì)糖基化可以按照氨基酸和糖的連接方式分為四類：O位糖基化、N位糖基化、C位甘露糖化以及 GPI(glycophosphatidlyinositol)錨定連接

二、Types of glycosylation

(Glycopeptide bonds can be categorized into specific groups based on the nature of the sugar–peptide bond and the oligosaccharide attached, including O-, N- and C-linked glycosylation, glypiation and phosphoglycosylation. )

 

1.  N-糖基化(N-linked glycosylation) 是通過(guò)糖鏈的的還原端N-乙酰胺基葡萄糖（Glc-Nac)和肽鏈中某些Asn側(cè)鏈酰胺基上的N原子相連，能接有糖鏈的Asn

必須處于Asn-X-Ser/Thr（X!=P)殘基構(gòu)成的基序中。糖為N-乙酰葡糖胺。

(1.N-linked glycosylation, is the attachment of the Glycan reducing end like N-acetylglucosamine (Glc-Nac) to to a nitrogen atom (the amide nitrogen of an asparagine (Asn) residue of a protein). N-linked glycans are almost always attached to the nitrogen atom of an asparagine (Asn) side chain that is present as a part of Asn–X–Ser/Thr(X!=P) consensus sequence, where X is any amino acid except proline (Pro).

 

2.  O-糖基化結(jié)構(gòu)比N-糖基化簡(jiǎn)單，一般糖鏈比較短，但是種類比N-糖基化多。肽鏈中可以糖基化的主要是Ser和Thr，此外還有酪氨酸、羥賴氨酸和羥脯氨酸，鏈接的位點(diǎn)是這些殘基側(cè)鏈上的羥基氧原子。連接的糖為半乳糖或N-乙酰半乳糖胺（Gal&GalNAc）{也可以葡萄糖/葡萄糖胺（Glc/GlcNAc）,甘露糖/甘露糖胺（Man/ManNAc）等，。

 

三、 糖基化位點(diǎn)

糖蛋白的基本結(jié)構(gòu)蛋白鏈與糖鏈通過(guò)共價(jià)鍵相連蛋白鏈上連接糖鏈的位點(diǎn)稱為糖基化位點(diǎn)。由于糖鏈的生物合成沒(méi)有模板可以遵循，因此在同一個(gè)糖基化位點(diǎn)上會(huì)連有不同的糖鏈，造成所謂的微觀不均一性。

 

 

四、 糖基化作用

1.  糖基化影響治療用蛋白的療效

  對(duì)于治療用蛋白，糖基化還可影響蛋白藥物在體內(nèi)的半衰期和靶向性

2.  糖基化與蛋白質(zhì)的可溶性

  研究表明，蛋白質(zhì)表面的糖鏈可增加蛋白質(zhì)的分子溶解性

3.  糖基化與蛋白質(zhì)的免疫原性

  一方面，蛋白質(zhì)表面的糖鏈可誘發(fā)特定的免疫反應(yīng)，另一方面，糖鏈又可遮蓋蛋白質(zhì)表面的某些表位而降低其免疫原性

4.  糖基化增加蛋白質(zhì)的穩(wěn)定性

  糖基化可增加蛋白質(zhì)對(duì)于各種變性條件（如變性劑、熱等）的穩(wěn)定性，防止蛋白的相互聚集。同時(shí)，蛋白表面的糖鏈還可覆蓋蛋白質(zhì)分子的某些蛋白酶降解位點(diǎn)，從而增加蛋白質(zhì)對(duì)于蛋白酶的抗性

5.  糖基化影響蛋白質(zhì)分子的生物活性

  改變蛋白質(zhì)的糖基化還可以使蛋白分子產(chǎn)生新的生物學(xué)活性

 

五、 蛋白質(zhì) O-GlcNAc 糖基化（（N-乙酰半胱氨酸（NAC））(GlcNAc N-乙酰葡糖胺/乙酰氨基葡糖）

1.  定義：?jiǎn)蝹€(gè) N-乙酰葡糖胺(N-acetylglucosamine, GlcNAc)在蛋白質(zhì)的絲氨酸或蘇氨酸殘基的羥基氧原子上進(jìn)行連接稱之為蛋白質(zhì) O-GlcNAc 糖基化。

 

O-GlcNA 糖基化是 O-GlcNAc單糖修飾，不存在糖鏈的延伸；像蛋白質(zhì)的磷酸化一樣，O-GlcNAc 糖基化也是一種動(dòng)態(tài)的蛋白質(zhì)修飾過(guò)程。

 

2.意義：O-GlcNAc 修飾異常可導(dǎo)致糖尿病、心血管疾病、腫瘤、阿爾茨海默病等多種疾病的發(fā)生。

 

 

六．提供常見(jiàn)單糖、雙糖、多糖產(chǎn)品服務(wù)

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