Glycoproteins can be divided into three main groups, based on the nature of the linkage between the polypeptide and oligosaccharide chains (Figure 1); there are other minor classes of glycoprotein:

 1. Those containing an O-glycosidic linkage (O-linked), involving the hydroxyl side chain of serine or threonine (and sometimes also tyrosine) and a sugar such as N-acetylgalactosamine (GalNAc-Ser[Thr]).

2. Those containing an N-glycosidic linkage (N-linked), , involving the amide nitrogen of asparagine and N-acetyl glucosamine (GlcNAc-Asn).

3. Those linked to the carboxyl-terminal amino acid of a protein via a phosphorylethanolamine moiety joined to an oligosaccharide (glycan), which in turn is linked via glucosamine to phosphatidylinositol (PI). These are glycosylphosphatidylinositol-anchored (GPI-anchored) glycoproteins. Among other functions, they are involved in directing glycoproteins to the apical or basolateral areas of the plasma membrane of polarized epithelial cells.

Fig1. The three main types of glycoprotein: (A) anO-linkage (N-acetylgalactosamine to serine), (B) an N-linkage (N-acetylglucosamine to asparagine), and (C) a glycosylphosphatidylinositol (GPI) linkage. The GPI structure shown is that linking acetylcholinesterase to the plasma membrane of the human red blood cell. The site of action of PI-phospholipase C (PI-PLC), which releases the enzyme from membrane binding is indicated. This particular GPI contains an extra fatty acid attached to inositol and also an extra phosphoryl ethanolamine moiety attached to the central of the mannose residue. Variations found among different GPI structures include the identity of the carboxyl-terminal amino acid, the molecules attached to the mannose residues, and the precise nature of the lipid moiety.

The number of oligosaccharide chains attached to one protein can vary from 1 to 30 or more, with the sugar chains ranging from one or two residues in length to much larger structures. The glycan chain may be linear or branched. Many proteins contain more than one type of sugar chain; for instance, glycophorin, an important red cell membrane glycoprotein, contains both O- and N-linked oligosaccharides.

اخر الاخبار

اخبار العتبة العباسية المقدسة

المجمع العلمي يواصل إقامة مسابقة الثقلين القرآنية لطلبة مدارس كربلاء

عضو مجلس إدارة العتبة العباسية المقدسة يطلع على آليات تطوير البرامج التعليمية في مجموعة العميد

مجموعة مناحل الكفيل تختتم مشاركتها في معرض السليمانية الدولي للزراعة والصناعات الغذائية

لتوثيق التراث العلمي.. وفد قسم شؤون المعارف يلتقي عددًا من أعلام مدينة النجف

المزيد

الآخبار الصحية

ثورة طبية.. الذكاء الاصطناعي يكشف سرطان الكلى في وقت قياسي

لتعزيز الطاقة والتغلب على التعب.. عليك بـ7 طرق بسيطة

لتحسين الهضم والتحكم في الشهية.. ما أفضل وقت لتناول التمر؟

خبراء يكشفون تأثير الاستحمام في الظلام على جودة النوم !

المزيد

الآخبار التكنلوجية

إزالة ثاني أكسيد الكربون من الغلاف الجوي.. ما دور المحيطات والبحار؟

نظائر الهيليوم مقياس لاكتشاف رواسب الذهب.. كيف ذلك؟

الصين تطلق أول ناقلة نفط خام ذكية في العالم تعمل بالميثانول

الزمن على المريخ أسرع من الأرض.. دراسة علمية تكشف الفوارق

المزيد

مواضيع ذات صلة

The Biosynthesis of N-Linked Glycoproteins Involves Dolichol-P-P-Oligosaccharide

Glycoproteins Contain Several Types of O-Glycosidic Linkages

Biochemical Markers of Bone Remodeling in Postmenopausal Osteoporosis

Biochemical Markers of Bone Remodeling in Different Clinical Conditions Affecting Bone Tissue Metabolism

Free Radicals & Antioxidant Nutrients

Vitamin B12 is Found only in Foods of Animal Origin

Vitamin B6 is important in Amino Acid & Glycogen Metabolism & in Steroid Hormone Action

Niacin is not Strictly A Vitamin

Bone Tissue Biochemistry

Vitamin K is required for synthesis of blood-clotting proteins

Vitamin E does not have a precisely defined metabolic function

Vitamin D is really a hormone