Galectin-4 Protein

CD19 is a type-I transmembrane glycoprotein of 95 kDa that belongs to the immunoglobulin superfamily and is widely expressed on B cells throughout most stages of B-cell differentiation, though its expression is down-regulated during their terminal differentiation to plasma cells. CD19 maps to chromosome 16p11.2, where it encodes a 540 amino acid protein with two extracellular C-type IgSF domains as well as a large, approximately 240 residue, cytoplasmic tail that exhibits extensive conservation between mice and humans. CD19 is a signal amplifying coreceptor whose expression is restricted to B cells and follicular dendritic cells. CD19 exists in a multimolecular complex with CD21 (complement receptor type 2, CR2), the tetraspanin CD81 and CD225 on the B cell surface. Via its interaction with CD21, CD19 serves as a signal transducing device for complement-conjugated antigen in B cells. Coligation of the BCR and the CD19/CD21 complex lowers the threshold for B cell activation by approximately two orders of magnitude. CD19 is a potential target for monoclonal antibody therapy, and preliminary data have demonstrated its effectiveness in B-cell depletion, making this an attractive therapy for autoimmune disorders and treatment of malignant B-cell lymphomas. CD19 serves as an attractive target for immunotherapy for many reasons: (1) It is expressed on most B-cell malignancies; (2) it is expressed in the B-cell lineage at an early stage, even before the expression of CD20; (3) it internalizes efficiently in lymphoma tumor models252; and (4) it is possibly involved in the development of B-cell cancers.Galectins are best known for their ability to bind glycoconjugates containing β-galactose, but classification of these small proteins within the galectin family is also defined by amino acid homology within structural domains and exon/intron junctions within genes. Galectin-4 (Gal4), a tandem-repeat type galectin, is expressed in healthy epithelium of the gastrointestinal tract. Altered levels of Gal4 expression are associated with different types of cancer, suggesting its usage as a diagnostic marker as well as target for drug development. The functional data available for this class of proteins suggest that the wide spectrum of cellular activities reported for Gal4 relies on distinct glycan specificity and structural characteristics of its two carbohydrate recognition domains. Gal4, a tandem-repeat-type lectin with affinity to sulfatide and non-sialylated termini of N-glycans, has the ability to regulate adhesion of cells to ECM components and is also involved in polarized membrane trafficking.