Expression cloning of the early activation antigen CD69, a type II integral membrane protein with a C-type lectin...

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• CD69 is an early activation antigen on T lymphocytes, a cell surface glycoprotein detected after lymphocyte stimulation.
• Despite extensive research on its biological activities, the molecular function of CD69 remains largely unknown.

Purpose of the Study:

• To investigate the molecular function of CD69.
• To clone the cDNA encoding CD69 and determine its protein structure and localization.

Main Methods:

• Cloning of CD69 cDNA based on expression in COS cells.
• Nucleotide sequencing and analysis of the open reading frame.
• In vitro translation and confirmation of molecular mass.
• Analysis of protein structure, including transmembrane regions and glycosylation sites.
• Proteinase K degradation assays to determine protein topology.
• Homology searches to identify related protein families.

Main Results:

• A cDNA clone (CD69.13) of 1676 bp was obtained, encoding a 199-amino acid protein with a predicted molecular mass of 22,559 Da.
• CD69 was identified as a type II membrane protein with an N-terminal cytoplasmic domain, a transmembrane region, and a C-terminal extracellular domain.
• Two glycosylated forms (26–28 kDa and 32–34 kDa) were detected in transfected COS cells and in vitro translation systems.
• Sequence homology indicated CD69 belongs to a supergene family of type II integral membrane proteins with a C-type lectin domain.

Conclusions:

• CD69 is a type II integral membrane protein with its N-terminus in the cytoplasm and C-terminus extracellular.
• The structural characteristics of CD69 suggest its involvement in signal transduction pathways.
• Further research into CD69's C-type lectin domain may elucidate its precise molecular function in T lymphocyte activation.