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Optimized Protocol for the Extraction of Proteins from the Human Mitral Valve
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Published on: June 14, 2017

The multiligand-binding protein gC1qR, putative C1q receptor, is a mitochondrial protein

J Dedio1, W Jahnen-Dechent, M Bachmann

  • 1Institute for Physiological Chemistry and Pathobiochemistry, Johannes Gutenberg University at Mainz, Germany.

Journal of Immunology (Baltimore, Md. : 1950)
|April 8, 1998
PubMed

Insights

The C1q receptor (gC1qR) is found in mitochondria, not on cell surfaces. This mitochondrial localization suggests its role as a complement receptor needs re-evaluation.

Area of Science:

  • Immunology
  • Cell Biology
  • Biochemistry

Background:

  • The 33 kDa protein (p33), also known as the globular C1q receptor (gC1qR), is believed to be the primary C1q receptor on immune cells.
  • The cellular localization and trafficking of p33/gC1qR have not been previously determined.

Purpose of the Study:

  • To investigate the subcellular localization and cellular routing of the p33/gC1qR.
  • To determine if p33/gC1qR is expressed on the cell surface or within intracellular compartments.

Main Methods:

  • Confocal laser-scanning microscopy was used to examine p33/gC1qR localization in cells.
  • Immunofluorescence microscopy and transfection studies with green fluorescent protein (GFP) fusion proteins were employed.
  • Immunocytochemistry was performed on fetal mouse tissues.

Main Results:

  • p33/gC1qR was found in intracellular compartments, colocalizing with the mitochondrial marker pyruvate dehydrogenase.
  • No surface expression of p33/gC1qR was detected on endothelial cells.
  • The N-terminal 33 amino acids of p33/gC1qR were sufficient to direct reporter proteins to mitochondria.
  • The mature p33/gC1qR protein (209 residues) was localized to the mitochondrial matrix and/or inner membrane.
  • p33/gC1qR showed ubiquitous expression in fetal mouse tissues, particularly in mitochondria-rich tissues.

Conclusions:

  • The candidate complement receptor p33/gC1qR is localized within mitochondria, not on the cell surface.
  • The intracellular localization of p33/gC1qR prevents its interaction with extracellular C1q.
  • The proposed function of p33/gC1qR as a cell surface C1q receptor requires reconsideration based on its mitochondrial localization.

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