IDENTIFICATION OF SEQUENCES MEDIATING GUANYLYL CYCLASE DIMERIZATION

Deletion mutagenesis was used to identify sequences required for dimer ization and enzymatic activity of the intracellular domain of the memb rane guanylyl cyclase, GC-A. The intracellular domain of GC-A contains a protein kinase-like domain near its amino terminus, a guanylyl cycl ase catalytic domain near its carboxyl terminus, and, between these do mains, a region of unknown function predicted to form an amphipathic a lpha-helix. Gel filtration analysis of deletion mutants of the GC-A in tracellular domain suggested that a 43 amino acid sequence within the interdomain region was both necessary and sufficient for dimerization and was required for guanylyl cyclase catalytic activity. The ability of this sequence to mediate protein dimerization was confirmed in the yeast two-hybrid system, in which its fusion to the lexA DNA-binding d omain and to the VP16 transcriptional activation domain led to their d imerization and consequent activation of a lexA-HIS3 gene. Thus, we ha ve identified sequences responsible for dimerization of the intracellu lar domain of a guanylyl cyclase and shown that they are required for enzyme activity. Modulation of their interaction may be important in g uanylyl cyclase activation.