<i>N</i>-Glycan on the Non-Consensus N-X-C Glycosylation Site Impacts Activity, Stability, and Localization of the Sd<sup>a</sup> Synthase B4GALNT2

<i>N</i>-Glycan on the Non-Consensus N-X-C Glycosylation Site Impacts Activity, Stability, and Localization of the Sd<sup>a</sup> Synthase B4GALNT2

The Sd<sup>a</sup> carbohydrate epitope and its biosynthetic B4GALNT2 enzyme are expressed in the healthy colon and down-regulated to variable extents in colon cancer. The human <i>B4GALNT2</i> gene drives the expression of a long and a short protein isoform (LF-B4GALNT2 and...

Full description

Bibliographic Details
Main Authors: Virginie Cogez, Dorothée Vicogne, Céline Schulz, Lucie Portier, Giulia Venturi, Jérôme de Ruyck, Mathieu Decloquement, Marc F. Lensink, Guillaume Brysbaert, Fabio Dall’Olio, Sophie Groux-Degroote, Anne Harduin-Lepers
Format: Article
Language:English
Published: MDPI AG 2023-02-01
Series:International Journal of Molecular Sciences
Subjects:
B4GALNT2
dimer
glycosyltransferase
<i>N</i>-glycan
unusual N-X-C glycosylation site
Online Access:https://www.mdpi.com/1422-0067/24/4/4139
Description
Summary:The Sd<sup>a</sup> carbohydrate epitope and its biosynthetic B4GALNT2 enzyme are expressed in the healthy colon and down-regulated to variable extents in colon cancer. The human <i>B4GALNT2</i> gene drives the expression of a long and a short protein isoform (LF-B4GALNT2 and SF-B4GALNT2) sharing identical transmembrane and luminal domains. Both isoforms are trans-Golgi proteins and the LF-B4GALNT2 also localizes to post-Golgi vesicles thanks to its extended cytoplasmic tail. Control mechanisms underpinning Sd<sup>a</sup> and B4GALNT2 expression in the gastrointestinal tract are complex and not fully understood. This study reveals the existence of two unusual <i>N</i>-glycosylation sites in B4GALNT2 luminal domain. The first atypical N-X-C site is evolutionarily conserved and occupied by a complex-type <i>N</i>-glycan. We explored the influence of this <i>N</i>-glycan using site-directed mutagenesis and showed that each mutant had a slightly decreased expression level, impaired stability, and reduced enzyme activity. Furthermore, we observed that the mutant SF-B4GALNT2 was partially mislocalized in the endoplasmic reticulum, whereas the mutant LF-B4GALNT2 was still localized in the Golgi and post-Golgi vesicles. Lastly, we showed that the formation of homodimers was drastically impaired in the two mutated isoforms. An AlphaFold2 model of the LF-B4GALNT2 dimer with an <i>N</i>-glycan on each monomer corroborated these findings and suggested that <i>N</i>-glycosylation of each B4GALNT2 isoform controlled their biological activity.
ISSN:1661-6596
1422-0067

Similar Items