The T3 complex on human T lymphocytes involves four structurally distinct glycoproteins.

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Monoclonal antibodies are crucial for identifying cell-specific antigens.
• The T3 complex on human thymus-derived lymphocytes is vital for T cell functions.

Purpose of the Study:

• To characterize the components of the T3 complex.
• To investigate the association and biosynthesis of T3 complex proteins.

Main Methods:

• Immunoprecipitation using anti-T3 reagents on surface-labeled cells.
• Enzymatic analysis with endo-beta-N-acetylglycosaminidase F.
• Peptide mapping and metabolic labeling experiments.

Main Results:

• The T3 complex comprises a 20-kDa glycoprotein and associated 25-28, 37, and 44 kDa glycoproteins.
• Polypeptide backbones of T3 components differ in molecular weight and pI.
• Metabolic labeling suggests the 25-28 kDa protein associates during biosynthesis, while 37/44 kDa proteins may associate post-translationally.
• A fifth, unglycosylated 20-kDa T3 species was identified.

Conclusions:

• The T3 complex is composed of multiple associated glycoproteins with distinct polypeptide chains.
• Differential association mechanisms (biosynthetic vs. cell surface) are proposed for T3 components.
• Further characterization of T3 complex structure and function is warranted.