Question

which test should be carried out to confirm the presence of glycoprotein present in a given solution​

Answer 1

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Figure 3. Structures of O-linked sugar chains found in hCG. Neu5Ac, N-acetylneuraminic acid; GalNAc, N-acetylgalactosamine. Other abbreviations are the same as in Fig. 2.

Detection of various N-linked sugar chains in hCG could be considered as a typical case of microheterogeneity, which is widely observed in the sugar chains of glycoproteins. However, comparative study of the N-linked sugar chains of hCGα and hCGβ revealed that sialylated N5 is distributed mainly in hCGβ and that sialylated N8 is distributed mainly in hCGα, whereas sialylated N6 is detected as a major sugar chain of both subunits. The specific distribution of different N-linked sugar chains at the four N-glycosylation sites of hCG molecule cannot be explained by our current knowledge of the biosynthetic mechanism of the N-linked sugar chains. An unknown control mechanism involving the steric effects of the polypeptide moiety may play a role in the formation of N-linked sugar chains of hCG. This assumption was supported by the study of the N-linked sugar chains of the free α-subunit.

A small amount of α-subunit occurs in free form in the urine of pregnant women. Interestingly, this free α-subunit cannot bind to hCGβ, in contrast to hCGα dissociated from hCG heterodimer. Because the free α-subunit has the same amino acid sequence as does hCGα, it was assumed that the free α-subunit contains different sugar chains from hCGα. Structural studies of the sugar chains of the free α-subunit revealed that it contains sialylated N5 as its major sugar chains. This evidence indicated that bulky sialylated N5 on the free α-subunit may sterically inhibit its association with hCGβ. Maturation of the N-linked sugar chains of the free α-subunit to larger complex-type sugar chains might be induced because the subunit did not bind to β-subunit. Therefore, uneven distribution of the N-linked sugar chains at the four N-glycosylation sites of hCG may be produced only when the two subunits are associated before the N-linked sugar chains start maturation at the Golgi apparatus.

Later on, the structures of the N-linked sugar chains of LH and TSH of various mammals, including human (hLH and hTSH), were elucidated (as shown in Fig. 4), as were those of human FSH (hFSH) (as shown in Fig. 5). In contrast to hCG, the three pituitary glycoprotein hormones contain triantennary and tetraantennary complex-type sugar chains, and their sialic acids are linked at the C-3 and C-6 positions of galactose residues. Occurrence of bisected sugar chains was also found. The most interesting evidence is that a part of the N-linked sugar chains of hLH and hTSH contain the SO44GalNAcβ14GlcNAc group as their outer chains.



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Figure 4. Structures of N-linked sugar chains found in LH and TSH. R represents the Neu5Acα23 or 6Galβ1 group, and R′ represents the SO44GalNAcβ1group. Abbreviations of the sugar units are the same

Answer 2

Answer:

Methods used for detection of glycoproteins in biological samples include chromatography [1], radioactive isotope labeling [2,3], fluorescence assay [1,4], and the ELISA method [5].

Explanation:

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