An unusual dual sugar-binding lectin domain controls the substrate specificity of a mucin-type O-glycosyltransferase

Sci Adv. 2024 Mar;10(9):eadj8829. doi: 10.1126/sciadv.adj8829. Epub 2024 Feb 28.


N-acetylgalactosaminyl-transferases (GalNAc-Ts) initiate mucin-type O-glycosylation, an abundant and complex posttranslational modification that regulates host-microbe interactions, tissue development, and metabolism. GalNAc-Ts contain a lectin domain consisting of three homologous repeats (α, β, and γ), where α and β can potentially interact with O-GalNAc on substrates to enhance activity toward a nearby acceptor Thr/Ser. The ubiquitous isoenzyme GalNAc-T1 modulates heart development, immunity, and SARS-CoV-2 infectivity, but its substrates are largely unknown. Here, we show that both α and β in GalNAc-T1 uniquely orchestrate the O-glycosylation of various glycopeptide substrates. The α repeat directs O-glycosylation to acceptor sites carboxyl-terminal to an existing GalNAc, while the β repeat directs O-glycosylation to amino-terminal sites. In addition, GalNAc-T1 incorporates α and β into various substrate binding modes to cooperatively increase the specificity toward an acceptor site located between two existing O-glycans. Our studies highlight a unique mechanism by which dual lectin repeats expand substrate specificity and provide crucial information for identifying the biological substrates of GalNAc-T1.

MeSH terms

  • Lectins
  • Mucins* / chemistry
  • Mucins* / metabolism
  • N-Acetylgalactosaminyltransferases* / chemistry
  • N-Acetylgalactosaminyltransferases* / genetics
  • N-Acetylgalactosaminyltransferases* / metabolism
  • Polypeptide N-acetylgalactosaminyltransferase
  • Protein Structure, Tertiary
  • Substrate Specificity
  • Sugars


  • Mucins
  • N-Acetylgalactosaminyltransferases
  • Lectins
  • Polypeptide N-acetylgalactosaminyltransferase
  • Sugars