O-Mannose Glycosylations Influence E-Cadherin Functional Interactions.

Cadherins are plasma membrane proteins that play critical roles in maintaining cell-cell adhesion and modulating cell signaling during development. Their functions are mediated by extracellular cadherin (EC) domains, which facilitate adhesive interactions and enable the formation of cis- and trans assemblies at adherens junctions and desmosomes. EC domains adopt a characteristic immunoglobulin-like fold composed of seven β-strands (A-G) and are modified by N-linked and O-linked glycosylations, including O-linked mannose monosaccharides (O-Man) on conserved serine and threonine residues of B- and G-strands. O-Man glycosylations on EC domains are catalyzed by the TMTC1-4 enzymes, with different TMTC enzymes modifying B- or G-strands. Given the site-specific deposition of O-Man glycans by dedicated enzymes and the central role of EC domains in cadherins' functions, we hypothesized that these PTMs may fine-tune cellular adhesion and otherwise contribute to diverse physical interactions that involve cadherins. To test these hypotheses, we assayed for changes in protein-protein interactions formed with epithelial (E)-cadherin in model cells where O-Man PTMs were genetically ablated. Herein, we report O-Man-dependent E-cadherin (CDH1) protein interactions, revealed by affinity proteomics, and we orthogonally validate an altered association between CDH1 and CDH3 (P-cadherin). We show different interactomic changes associated with O-Man ablation on B- vs. G-strands, highlighting the importance of these PTMs in CDH1-associated interactions, and we confirm compromised cell-cell adhesion attributable to TMTC3 loss (O-Man ablation from EC G-strands). These findings provide new insights into how O-Man regulates CDH1-dependent protein complexes.