Structure and function of gC1q-R: a multiligand binding cellular protein

Area of Science:

• Molecular Biology
• Immunology
• Cell Biology

Background:

• gC1q-R (complement C1q receptor) is a 33 kDa acidic protein initially isolated from Raji cells.
• It binds to the globular heads of C1q but is now recognized as a multifunctional protein with diverse ligand affinities.
• gC1q-R is identical to transcription factors SF2 and TAP, encoded by a single gene on chromosome 17p13.3 in humans.

Purpose of the Study:

• To investigate the localization and potential functions of gC1q-R.
• To explore the evidence for gC1q-R expression on both intracellular and cell surface compartments.

Main Methods:

• Analysis of gC1q-R protein sequence and gene localization.
• Use of monoclonal antibodies (mAbs) to detect gC1q-R on Raji cells.
• Cell surface labeling with sulfo-NHS-LC-biotin to differentiate surface and intracellular gC1q-R.
• Upregulation studies using inflammatory cytokines (INF-gamma, TNF-alpha, LPS).

Main Results:

• gC1q-R binds to multiple ligands including thrombin, vitronectin, and high molecular weight kininogen.
• The mature form of gC1q-R (residues 74-282) is generated by post-translational processing.
• Evidence supports gC1q-R expression on both the cell surface and intracellularly, with surface expression enhanced by poly-L-lysine and inflammatory cytokines.

Conclusions:

• gC1q-R is a multifunctional protein with a dual localization (intracellular and cell surface).
• Its cell surface expression is dynamic and can be modulated by inflammatory signals.
• gC1q-R likely plays significant biological roles in both cellular compartments.