Involvement of the alpha2,8-polysialyltransferases II/STX and IV/PST in the biosynthesis of polysialic acid chains on the O-linked glycoproteins in rainbow trout ovary.
Polysialoglycoprotein (PSGP) in salmonid fish egg is a unique glycoprotein bearing alpha2,8-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 alpha2,8-polysialyltransferases (alpha2,8-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 alpha2,8-polySTs are involved in the biosynthesis of polySia on O-linked glycans in any glycoproteins. We thus sought to identify cDNA encoding the alpha2,8-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 alpha2,8-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 alpha2,8-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.
Asahina
Shinji
S
Laboratory of Animal Cell Function, Bioscience and Biotechnology Center, Department of Bioengineering Sciences, Nagoya University, Nagoya 464-8601.
Sato
Chihiro
C
Matsuno
Midori
M
Matsuda
Tsukasa
T
Colley
Karen
K
Kitajima
Ken
K
D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D019556:COS Cells; D002522:Chlorocebus aethiops; D005260:Female; D015870:Gene Expression; D008297:Male; D053858:Metabolic Networks and Pathways; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss; D009866:Oogenesis / Q000502:physiology; D010053:Ovary / Q000201:enzymology*; D011134:Polysaccharides / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D012794:Sialic Acids / Q000096:biosynthesis; D012795:Sialoglycoproteins / Q000096:biosynthesis*; D012799:Sialyltransferases / Q000378:metabolism*; D014018:Tissue Distribution; D014162:Transfection
D011134:Polysaccharides; D012794:Sialic Acids; D012795:Sialoglycoproteins; C021319:polysialic acid; C046778:CMP-N-acetylneuraminate-poly-alpha-2,8-sialosyl sialyltransferase; D012799:Sialyltransferases