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Shown following is the first 30 amino acid region of this putative amino acid sequence for p77:

1YFNPT     6DSWPT    11LAPAN    16YSFLF    21FLARY    26WYINL30

Based on the partial amino acid sequence provided for p77,

a. which amino acids in the sequence provide may be glycosylated and how can you identify these potential sites?

b. and with which type of glycosylation might they be modified?

c. and explain how these modifications are made,

d. and explain where these modifications are made in the cell,

e. and finally, explain what effects glycosylation might have on the protein.

Explanation / Answer

Glycosylation is a process by which a carbohydrate molecule is added to the hydroxyl group or any other functional group of the protein.

a and b. Two types of glycosylation happens, N-linked which will happen on Aspargine and ariginine residues of the protein. In the protein sequence amino acids numbers 3 (N), 15 (N), 24 (R) and 29 (N) will be N-linked glycosylated.

O-linked will happen on serine, theronine and tyrosine residues. In the protein sequence amino acids numbers 1 (Y), 7 (S), 10 (T), 17 (S), 25 (Y), and 27 (Y) will be O-linked glycosylated.

c. Glycosylation is a form of co-translational and post translational modification. Glycosylation is an enzymatic process, the donor molecule is often an activated nucleotide sugar. Therefore it is site specfic modification.

d. N-linked glycosylation happens in the lumen of endoplasmic reticulum and O-linked glycosylation happens in golgi appartus.

e. Glycosylation of proteins is essential for their proper folding, it plays an role in cell to cell adhesion and glycosylation also controls the protein function by acting as a on-off switch.

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