Polysialyltransferase-1 autopolysialylation is not requisite for polysialylation of neural cell adhesion molecule

J Biol Chem. 2000 Feb 11;275(6):4484-91. doi: 10.1074/jbc.275.6.4484.

Abstract

Polysialyltransferase-1 (PST; ST8Sia IV) is one of the alpha2, 8-polysialyltransferases responsible for the polysialylation of the neural cell adhesion molecule (NCAM). The presence of polysialic acid on NCAM has been shown to modulate cell-cell and cell-matrix interactions. We previously reported that the PST enzyme itself is modified by alpha2,8-linked polysialic acid chains in vivo. To understand the role of autopolysialylation in PST enzymatic activity, we employed a mutagenesis approach. We found that PST is modified by five Asn-linked oligosaccharides and that the vast majority of the polysialic acid is found on the oligosaccharide modifying Asn-74. In addition, the presence of the oligosaccharide on Asn-119 appeared to be required for folding of PST into an active enzyme. Co-expression of the PST Asn mutants with NCAM demonstrated that autopolysialylation is not required for PST polysialyltransferase activity. Notably, catalytically active, non-autopolysialylated PST does not polysialylate any endogenous COS-1 cell proteins, highlighting the protein specificity of polysialylation. Immunoblot analyses of NCAM polysialylation by polysialylated and non-autopolysialylated PST suggests that the NCAM is polysialylated to a higher degree by autopolysialylated PST. We conclude that autopolysialylation of 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
  • COS Cells
  • Fluorescent Antibody Technique
  • Immunoblotting
  • Mutagenesis, Site-Directed
  • Mutation
  • Neural Cell Adhesion Molecules / metabolism*
  • Precipitin Tests
  • Sialic Acids / chemistry
  • Sialyltransferases / genetics
  • Sialyltransferases / metabolism*

Substances

  • Neural Cell Adhesion Molecules
  • Sialic Acids
  • polysialic acid
  • Asparagine
  • Sialyltransferases