Question

Why are protein differ from one another in sugar content and structure ?

Give three reasons why chemical difference affects the 2D gel behaviour of the isoforms present.

Answer 1

Answer: Protein glycosylation is the posttranslational modification. Mostly secretory and membrane proteins are glycosylation. The pattern and nature varies from protein to protein as there are different glycosylating enzymes present in the cells. Also some of the proteins are have N-linked glycosylation whereas others have O-linked glycosylation., O-linked oligosaccharides are linked to the OH-group of serine or threonine via N-acetylgalactosamine (GalNac) or (in collagens) to the hydroxyl group of hydroxylysine via galactose and are generally short, containing only 1-4 sugars. On the otherhand, N-linked oligosaccharides, N-acetylglucosamine (GlcNAc) is linked to the amide nitrogen of asparagine and they always contains mannose as well as N-acetylglucosamine and usually have several branches each terminating with a negatively charged sialic acid residue

Answer; The separation of proteins by 2D gel electrophoresis is based on their difference in charge, size as well as conformation. Chemical modifications like phosphorylation changes the charge on the protein molecules and thus their behavior in 2D gel electrophoresis.