The polysialyltransferase ST8Sia II/STX: posttranslational processing and role of autopolysialylation in the polysialylation of neural cell adhesion molecule

Glycobiology. 2001 Nov;11(11):997-1008. doi: 10.1093/glycob/11.11.997.


The presence of alpha2,8-linked polysialic acid on the neural cell adhesion molecule (NCAM) is known to modulate cell interactions during development and oncogenesis. Two enzymes, the alpha2,8-polysialyltransferases ST8Sia IV()/PST and ST8Sia II()/STX are responsible for the polysialylation of NCAM. We previously reported that both ST8Sia IV/PST and ST8Sia II/STX enzymes are themselves modified by alpha2,8-linked polysialic acid chains, a process called autopolysialylation. In the case of ST8Sia IV/PST, autopolysialylation is not required for enzymatic activity. However, whether the autopolysialylation of ST8Sia II/STX is required for its ability to polysialylate NCAM is unknown. To understand how autopolysialylation impacts ST8Sia II/STX enzymatic activity, we employed a mutagenesis approach. We found that ST8Sia II/STX is modified by six Asn-linked oligosaccharides and that polysialic acid is distributed among the oligosaccharides modifying Asn 89, 219, and 234. Coexpression of a nonautopolysialylated ST8Sia II/STX mutant with NCAM demonstrated that autopolysialylation is not required for ST8Sia II/STX polysialyltransferase activity. In addition, catalytically active, nonautopolysialylated ST8Sia II/STX does not polysialylate any endogenous COS-1 cell proteins, highlighting the protein specificity of polysialylation. Furthermore, immunoblot analysis of NCAM polysialylation by autopolysialylated and nonautopolysialylated ST8Sia II/STX suggests that the NCAM is polysialylated to a higher degree by autopolysialylated ST8Sia II/STX. Therefore, we conclude that autopolysialylation of ST8Sia II/STX, like that of ST8Sia IV/PST, is not required for, but does enhance, NCAM polysialylation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Asparagine / chemistry
  • Base Sequence
  • Binding Sites
  • COS Cells
  • DNA, Complementary / genetics
  • Glycosylation
  • Mutagenesis, Site-Directed
  • Neural Cell Adhesion Molecule L1*
  • Neural Cell Adhesion Molecules / metabolism*
  • Oligosaccharides / chemistry
  • Protein Processing, Post-Translational
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sialic Acids / metabolism*
  • Sialyltransferases / chemistry
  • Sialyltransferases / genetics
  • Sialyltransferases / metabolism*


  • DNA, Complementary
  • Neural Cell Adhesion Molecule L1
  • Neural Cell Adhesion Molecules
  • Oligosaccharides
  • Recombinant Proteins
  • Sialic Acids
  • polysialyl neural cell adhesion molecule
  • Asparagine
  • Sialyltransferases