Question

GalNAc (N-acetylgalactosamine) is known to form an attachment point for carbohydrates to See residues on surface of proteins. Draw structure of GalNAc 'O-linked' to See residue in the beta-anomer configuration.

Answer 1

Hi i would like to first explain alpha & beta positions by taking glucopyranose as an example. At anomeric carbon center if OH group is in above the plane then we name it as beta-anomer and if the OH group is in below the plane then we name it as alpha-anomer. Please see below figure.

Coming to the actual problem structure of GalNAc 'O-linked' to See residue in the beta-anomer configuration. Serine (Ser) amino acid is O-linked with GalNAc in beta-anomeric position as below.

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