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Journal of Biochemistry Advance Access published online on October 5, 2006
Journal of Biochemistry, doi:10.1093/jb/mvj200
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© 2006 The Japanese Biochemical Society.
Received July 11, 2006
Accepted September 21, 2006

Regular Paper

Involvement of the {alpha}2,8-Polysialyltransferases II/STX and IV/PST in the Biosynthesis of Polysialic Acid Chains on the O-Linked Glycoproteins in Rainbow Trout Ovary

Shinji Asahina 1, Chihiro Sato 1, Midori Matsuno 2, Tsukasa Matsuda 2, Karen Colley 3, and Ken Kitajima 4 *

1 Laboratory of Animal Cell Function, Bioscience and Biotechnology Center, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan; Department of Bioengineering Sciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
2 Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
3 Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago College of Medicine, IL 60607, U.S.A
4 Laboratory of Animal Cell Function, Bioscience and Biotechnology Center, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan; Department of Bioengineering Sciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan; Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan

* To whom correspondence should be addressed.
Ken Kitajima, E-mail: kitajima{at}agr.nagoya-u.ac.jp


  Abstract

Polysialoglycoprotein (PSGP) in salmonid fish egg is a unique glycoprotein bearing {alpha}2,8-linked polysialic acid (polySia) on its O-linked glycans. Biosynthesis of the polySia chains is developmentally regulated and only occurs at later stage of oogenesis. Two {alpha}2,8-polysialyltransferases ({alpha}2,8-polySTs), PST (ST8Sia IV) and STX (ST8Sia II), responsible for the biosynthesis of polySia on N-glycans of glycoproteins, are known in mammals. However, nothing has been known about which {alpha}2,8-polySTs are involved in the biosynthesis of polySia on O-linked glycans in any glycoproteins. We thus sought to identify cDNA encoding the {alpha}2,8-polyST involved in polysialylation of PSGP. A clone for PST orthologue, rtPST, and two clones for the STX orthologue, rtSTX-ov and rtSTX-em, were identified in rainbow trout. The deduced amino acid sequence of rtPST shows a high identity (72-77%) to other vertebrate PSTs, while that of rtSTX-ov shows 92% identity with rtSTX-em and a significant identity (63-76%) to other vertebrate STXs. The rtPST exhibited the in vivo {alpha}2,8-polyST activity, although its in vitro activity was low. However, the rtSTXs showed no in vivo and very low in vitro activities. Interestingly, co-existence of rtPST and rSTX-ov in the reaction mixture synergistically enhanced the {alpha}2,8-polyST activity. During oogenesis, rtPST was constantly expressed, while the expression of rtSTX-ov was not increased until polySia chain is abundantly biosynthesized in the later stage. rtSTX-em was not expressed in ovary. These results suggest that the enhanced expression of rtSTX-ov under the co-expression with rtPST may be important for the biosynthesis of polySia on O-linked glycans of PSGP.

Keywords: polysialyltransferase; polysialoglycoprotein; polysialic acid; O-linked glycan; cortical alveolus; oocyte development; rainbow trout.
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