O-glycosylation in Toxoplasma gondii: identification and analysis of a family of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases

Int J Parasitol. 2004 Mar 9;34(3):309-22. doi: 10.1016/j.ijpara.2003.11.016.

Abstract

The initiation of mucin-type O-glycosylation is catalysed by a family of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases (EC 2.4.1.41). These enzymes are responsible for the transfer of N-acetylgalactosamine from the nucleotide sugar donor, UDP-GalNAc, to the hydroxyl group on specific serine or threonine residues in acceptor proteins. By screening a Toxoplasma gondii cDNA library, three distinct isoforms of the ppGalNAc-T gene family were cloned. Two additional isoforms were identified and partially cloned following analysis of the T. gondii genome sequence database. All of the cloned and identified ppGalNAc-T's are type II membrane proteins that share up to 50% amino acid sequence identity within the conserved catalytic domain. They each contain an N-terminal cytoplasmic domain, a hydrophobic transmembrane domain, and a lumenal domain; the latter consists of stem, catalytic, and lectin-like domains. Moreover, each of this ppGalNAc-T's contains important sequence motifs that are typical for this class of glycosyltransferases. These include a glycosyltransferase 1 motif containing the DXH sequence, a Gal/GalNAc-T motif, and the CLD and QXW sequence motifs located in alpha-, beta-, and gamma-repeats present within the lectin-like domain. The coding regions of T. gondii ppGalNAc-T1, -T2, and -T3 reside in multiple exons ranging in number from 6 to 10. Our results demonstrate that mucin-type O-glycosylation in T. gondii is catalysed by a multimember gene family, which is evolutionarily conserved from single-celled eukaryotes through nematodes and insects up to mammals. Taken together, this information creates the basis for future studies of the function of the ppGalNAc-T gene family in the pathobiology of this apicomplexan parasite.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • DNA, Complementary / genetics
  • DNA, Protozoan / genetics
  • Genes, Protozoan
  • Glycosylation
  • Molecular Sequence Data
  • N-Acetylgalactosaminyltransferases / genetics
  • N-Acetylgalactosaminyltransferases / metabolism*
  • Phylogeny
  • Sequence Alignment
  • Toxoplasma / enzymology*
  • Toxoplasma / genetics
  • Uridine Diphosphate N-Acetylgalactosamine / genetics
  • Uridine Diphosphate N-Acetylgalactosamine / metabolism*

Substances

  • DNA, Complementary
  • DNA, Protozoan
  • Uridine Diphosphate N-Acetylgalactosamine
  • N-Acetylgalactosaminyltransferases
  • polypeptide N-acetylgalactosaminyltransferase

Associated data

  • GENBANK/AF234624
  • GENBANK/AF321881
  • GENBANK/AY136814
  • GENBANK/AY160970
  • GENBANK/AY424889
  • GENBANK/AY424890
  • GENBANK/AY424891
  • GENBANK/AY424892