The dimeric structure of wild-type human glycosyltransferase B4GalT1

PLoS One. 2018 Oct 23;13(10):e0205571. doi: 10.1371/journal.pone.0205571. eCollection 2018.


Most glycosyltransferases, including B4GalT1 (EC, are known to assemble into enzyme homomers and functionally relevant heteromers in vivo. However, it remains unclear why and how these enzymes interact at the molecular/atomic level. Here, we solved the crystal structure of the wild-type human B4GalT1 homodimer. We also show that B4GalT1 exists in a dynamic equilibrium between monomer and dimer, since a purified monomer reappears as a mixture of both and as we obtained crystal forms of the monomer and dimer assemblies in the same crystallization conditions. These two crystal forms revealed the unliganded B4GalT1 in both the open and the closed conformation of the Trp loop and the lid regions, responsible for donor and acceptor substrate binding, respectively. The present structures also show the lid region in full in an open conformation, as well as a new conformation for the GlcNAc acceptor loop (residues 272-288). The physiological relevance of the homodimer in the crystal was validated by targeted mutagenesis studies coupled with FRET assays. These showed that changing key catalytic amino acids impaired homomer formation in vivo. The wild-type human B4GalT1 structure also explains why the variant proteins used for crystallization in earlier studies failed to reveal the homodimers described in this study.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • COS Cells
  • Chlorocebus aethiops
  • Escherichia coli
  • Galactosyltransferases / chemistry
  • Galactosyltransferases / genetics
  • Galactosyltransferases / isolation & purification
  • Galactosyltransferases / metabolism*
  • Humans
  • Models, Molecular
  • Mutation
  • Protein Conformation
  • Protein Domains
  • Protein Multimerization


  • Galactosyltransferases
  • beta-1,4-galactosyltransferase I

Grants and funding

This work has been funded by the Academy of Finland (no. 285232 to Dr. Sakari Kellokumpu), University of Oulu, and Emil Aaltonen Foundation (to Dr. Antti Hassinen). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.