Human soluble guanylate cyclase: functional expression and revised isoenzyme family

Soluble guanylate cyclase (sGC), a heterodimeric (alpha/beta) 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 (alpha 1-alpha 3, beta 1-beta 3) 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 alpha/beta 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 alpha and beta subunits were detected in human tissues, suggesting co-expression also in vivo. Moreover, resequencing of the human cDNA clones [originally termed alpha 3 and beta 3; Giuili, Scholl, Bulle and Guellaen (1992) FEBS Lett. 304, 83-88] revealed several sequencing errors in human alpha 3; correction of these eliminated major regions of divergence from rat and bovine alpha 1. As human beta 3 also displays more than 98 % similarity to rat and bovine beta 1 at the amino acid level, alpha 3 and beta 3 represent the human homologues of rat and bovine alpha 1 and beta 1, and the isoenzyme family is decreased to two isoforms for each subunit (alpha 1, alpha 2; beta 1, beta 2). Having access to the human key enzyme of NO signalling will now permit the study of novel sGC-modulating compounds with therapeutic potential.