We have identified a novel membrane form of guanylate cyclase (GC) from a mouse testis cDNA library and termed it mGC-G (mouse GC-G) based on its high sequence homology to rat GC-G. It encodes a potential type I transmembrane receptor, with the characteristic domain structure common to all members of the family of membrane GCs, including an extracellular, putative ligand-binding domain, a single membrane-spanning segment and cytoplasmic protein kinase-like and cyclase catalytic domains. Real-time quantitative reverse transcriptase–PCR and Northern-blot analyses showed that mGC-G is highly and selectively expressed in mouse testis. Phylogenetic analysis based on the extracellular protein sequence revealed that mGC-G is closely related to members of the subfamily of natriuretic peptide receptor GCs. When overexpressed in HEK-293T cells (human embryonic kidney 293T cells) or COS-7 cells, mGC-G manifests as a membrane-bound glycoprotein, which can form either homomeric or heteromeric complexes with the natriuretic peptide receptor GC-A. It exhibits marked cGMP-generating GC activity; however, notably, all ligands known to activate other receptor GCs failed to stimulate enzymic activity. The unique testis-enriched expression of mGC-G, which is completely different from the broader tissue distribution of rat GC-G, suggests the existence of as-yet-unidentified ligands and unappreciated species-specific physiological functions mediated through mGC-G/cGMP signalling in the testis.
- guanylate cyclase
- signal transduction
Abbreviations used: DMEM, Dulbecco's modified Eagle's medium; ECD, extracellular domain; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GC, guanylate cyclase; mGC-G and rGC-G, mouse and rat GC-G respectively; IBMX, isobutylmethylxanthine; SIN-1, 3-morpholinosydnonimine; NP, natriuretic peptide; ANP, BNP and CNP, atrial, B-type and C-type NPs respectively; RT, reverse transcriptase.
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