Polysialyltransferase-1 Autopolysialylation Is Not Requisite for Polysialylation of Neural Cell Adhesion Molecule

Polysialyltransferase-1 (PST; ST8Sia IV) is one of the α2,8-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 t...

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Bibliographic Details
Published in:The Journal of biological chemistry 2000-02, Vol.275 (6), p.4484-4491
Main Authors: Close, Brett E., Tao, Kevin, Colley, Karen J.
Format: Article
Language:English
Subjects:
Animals
Asparagine - chemistry
COS Cells
Fluorescent Antibody Technique
Immunoblotting
Mutagenesis, Site-Directed
Mutation
Neural cell adhesion molecule
Neural Cell Adhesion Molecules - metabolism
polysialic acid
Polysialyltransferase 1
Precipitin Tests
Sialic Acids - chemistry
Sialyltransferases - genetics
Sialyltransferases - metabolism
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Summary:Polysialyltransferase-1 (PST; ST8Sia IV) is one of the α2,8-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 α2,8-linked polysialic acid chainsin 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.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.275.6.4484