Human soluble guanylate cyclase: functional expression and revised isoenzyme family

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Abstract
Soluble guanylate cyclase (sGC), a heterodimeric (α/β) haem protein that converts GTP to the second messenger cGMP, functions as the receptor for nitric oxide (NO) and nitrovasodilator drugs. Three distinct cDNA species of each subunit (α1–α3, β1–β3) have been reported from various species. From human sources, none of these have been expressed as functionally active enzyme. Here we describe the expression of human α/β heterodimeric sGC in Sf9 cells yielding active recombinant enzyme that was stimulated by the nitrovasodilator sodium nitroprusside or the NO-independent activator 3-(5´-hydroxymethyl-2´-furyl)-1-benzylindazole (YC-1). At the protein level, both α and β subunits were detected in human tissues, suggesting co-expression also in vivo. Moreover, resequencing of the human cDNA clones [originally termed α3 and β3; Giuili, Scholl, Bulle and Guellaen (1992) FEBS Lett. 304, 83–88] revealed several sequencing errors in human α3; correction of these eliminated major regions of divergence from rat and bovine α1. As human β3 also displays more than 98% similarity to rat and bovine β1 at the amino acid level, α3 and β3 represent the human homologues of rat and bovine α1 and β1, and the isoenzyme family is decreased to two isoforms for each subunit (α1, α2; β1, β2). Having access to the human key enzyme of NO signalling will now permit the study of novel sGC-modulating compounds with therapeutic potential.