Guanylyl cyclase c

Guanylyl cyclase c, or GC-C, is an enzyme found only in the luminal aspect of intestinal epithelium. The receptor has an extracellular ligand-binding domain, a single transmembrane region, a region with sequence similar to that of protein kinases, and a C-terminal guanylyl cyclase domain. Tyrosine kinase activity mediates the GC-C signaling pathway within the cell.

Functions
GC-C is a key receptor for heat-stable enterotoxins which are responsible for acute secretory diarrhea. Heat-stable enterotoxins are produced by pathogens such as Escherichia coli. Knockout mice defficient in the GC-C gene do not show secretory diarrhea on infection with E. coli, though they do with cholera toxin. This demonstrates the specificity of the GC-C receptor.

Diagnostic application
Because GC-C is tissue-specific for intestinal epithelium, it can be used for exceedingly precise detection of metastatic disease. The presence of GC-C mRNA can be detected at a rate of a single cancer cell out of 10,000,000 normal cells. This is the most precise staging tool available.