Leukosialin, a major sialoglycoprotein defining leucocyte differentiation

Area of Science:

• Immunology
• Glycobiology
• Cell Biology

Background:

• Leukocytes express various glycoproteins crucial for immune function.
• Sialoglycoproteins play significant roles in cell recognition and signaling.

Purpose of the Study:

• To isolate and characterize a major sialoglycoprotein on human leukocytes.
• To investigate the structure and modifications of this glycoprotein, termed leukosialin, across different leukocyte types and activation states.

Main Methods:

• Isolation of leukosialin from human leukocytes.
• Biochemical analysis of glycoprotein structure, including polypeptide mass and glycosylation.
• Amino acid sequencing using cDNA to identify O-glycan attachment sites.
• Structural analysis of O-linked oligosaccharides.

Main Results:

• Leukosialin is ubiquitously present on human granulocytes, monocytes/macrophages, and T lymphocytes.
• Leukosialin is heavily glycosylated with O-linked oligosaccharides (approx. 70 chains/molecule) on a 38.5 kDa polypeptide.
• The external domain shows extensive O-glycan modification (approx. 70% of serine/threonine residues).
• O-glycan structures are cell lineage and maturation-stage specific.
• A specific conversion of O-glycan structures was observed during T cell activation.

Conclusions:

• Leukosialin is a key sialoglycoprotein found across diverse human leukocyte populations.
• The extensive and variable O-glycosylation of leukosialin suggests its importance in leukocyte function and regulation.
• Dynamic changes in leukosialin O-glycans during T cell activation highlight its role in immune responses.