Molecular cloning and expression of human UDP-d-Xylose:proteoglycan core protein beta-d-xylosyltransferase and its first isoform XT-II

J Mol Biol. 2000 Dec 8;304(4):517-28. doi: 10.1006/jmbi.2000.4261.


Human UDP-d-xylose:proteoglycan core protein beta-d-xylosyltransferase (EC, XT-I) initiates the biosynthesis of glycosaminoglycan chains in proteoglycans by transferring xylose from UDP-xylose to specific serine residues of the core protein. Based on the partial amino acid sequence of the purified enzyme from human JAR choriocarcinoma cell culture supernatant we isolated a cDNA encoding XT-I using the degenerate reverse transcriptase-polymerase chain reaction method. This enzyme, which is involved in chondroitin sulfate, heparan sulfate, heparin and dermatan sulfate biosynthesis, belongs to a novel family of glycosyltransferases with no homology to proteins known so far. 5' and 3'-RACE were performed to isolate a novel cDNA fragment of 3726 bp with a single open reading frame encoding at least 827 amino acid residues with a molecular mass of 91 kDa. The human XT-I gene was located on chromosome 16p13.1 using radiation hybrid mapping, and extracts from CHO-K1 cells transfected with the XT-I cDNA in an expression vector exhibited marked XT activity. A new 3608 bp cDNA fragment encoding a protein of 865 amino acid residues was also isolated by PCR using degenerate primers based on the amino acid sequence of human XT-I. The amino acid sequence of this XT-II isoform displayed 55% identity to the human XT-I. The XT-II gene was located on chromosome 17q21.3-17q22, and the exon/intron structure of the 15 kb gene was determined. RT-PCR analyses of XT-I and XT-II mRNA from various tissues confirmed that both XT-I and XT-II transcripts are ubiquitously expressed in the human tissues, although with different levels of transcription. Furthermore, the cDNAs encoding XT-I and XT-II from rat were cloned. The deduced amino acid sequences of rat xylosyltransferases displayed 94% identity to the corresponding human enzyme.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Brain / metabolism
  • CHO Cells
  • Chondrocytes / metabolism
  • Chromosomes, Human, Pair 16 / genetics
  • Chromosomes, Human, Pair 17 / genetics
  • Cloning, Molecular
  • Cricetinae
  • Exons / genetics
  • Humans
  • Introns / genetics
  • Isoenzymes / chemistry
  • Isoenzymes / genetics
  • Isoenzymes / metabolism
  • Molecular Sequence Data
  • Open Reading Frames / genetics
  • Organ Specificity
  • Pentosyltransferases / chemistry
  • Pentosyltransferases / genetics*
  • Pentosyltransferases / metabolism*
  • Polymerase Chain Reaction
  • Radiation Hybrid Mapping
  • Rats
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Sequence Alignment
  • Transfection
  • Tumor Cells, Cultured
  • UDP Xylose-Protein Xylosyltransferase


  • Isoenzymes
  • Recombinant Proteins
  • Pentosyltransferases