Peptides derived from human galectin-3 N-terminal tail interact with its carbohydrate recognition domain in a phosphorylation-dependent manner

Abstract

Galectin-3 (Gal-3) is a multifunctional effector acting extracellularly after non-classical secretion, in the cytoplasm and the nucleus. Its modular display of a carbohydrate recognition domain (CRD) attached to a tail of collagen-like repeats (nine in the human protein) and an N-terminal peptide is unique in this lectin family and not yet fully explored, as is the physiological significance of serine and tyrosine phosphorylation. Using a series of nine synthetic (phospho)peptides and the 15N-labeled CRD of human Gal-3 as well as measuring chemical shift perturbations in mixtures, potential for peptide reactivity was revealed in Gal-3’s backface. Tyrosine phosphorylation reduced the affinity, while serine phosphorylation of the N-terminal peptide was essential. Controls with sequence scrambling underscored inherent specificity. These results detect capacity for distinct sites of intramolecular recognition in Gal-3, adjustable by phosphorylation, and thus prompt analysis using the full-length protein.