The beta2 subunit inhibits stimulation of the alpha1/beta1 form of soluble guanylyl cyclase by nitric oxide. Potential relevance to regulation of blood pressure.

Abstract

Cytosolic guanylyl cyclases (GTP pyrophosphate-lyase [cyclizing; EC 4.6.1.2]), primary receptors for nitric oxide (NO) generated by NO synthases, are obligate heterodimers consisting of an ␣ and a ␤ subunit. The ␣ 1/ ␤ 1 form of guanylyl cyclase has the greatest activity and is considered the universal form. An isomer of the ␤ 1 subunit, i.e., ␤ 2, has been detected in the liver and kidney, however, its role is not known. In this study, we investigated the function of ␤ 2. Immunoprecipitation experiments showed that the ␤ 2 subunit forms a heterodimer with the ␣ 1 subunit. NO-stimulated cGMP formation in COS 7 cells cotransfected with the ␣ 1 and ␤ 2 subunits was ‫ف‬ 1/3 of that when ␣ 1 and ␤ 1 subunits were cotransfected. The ␤ 2 subunit inhibited NO-stimulated activity of the ␣ 1/ ␤ 1 form of guanylyl cyclase and NOstimulated cGMP formation in cultured smooth muscle cells. Our results provide the first evidence that the ␤ 2 subunit can regulate NO sensitivity of the ␣ 1/ ␤ 1 form of guanylyl cyclase. Northern analysis for guanylyl cyclase subunits was performed on RNA from kidneys of Dahl salt-sensitive rats, which have been shown to have decreased renal sensitivity to NO. Compared to the Dahl salt-resistant rat, message for ␤ 2 was increased, ␤ 1 was decreased, and ␣ 1 was unchanged. These results suggest a molecular basis for decreased renal guanylyl cyclase activity, i.e., an increase in the ␣ 1/ ␤ 2 heterodimer, and decrease in the ␣ 1/ ␤ 1 heterodimer. (

Structural and Functional Characterization of the Dimerization Region of Soluble Guanylyl Cyclase

“…Notably various isoforms of human and rat ␤ 2 expressed in kidney, liver, and brain (19,32) are characterized by N-terminal truncations of up to 79 residues and C-terminal extensions of up to 63 residues compared with the corresponding ␤ 1 subunits (19,33,34). Among these, the rat ␤ 2 isoform has been shown to reduce considerably the activity of coexpressed ␣ 1 ␤ 1 in vitro, and therefore enhanced expression of ␤ 2 has been implicated in the downregulation of renal guanylyl cyclase activity in Dahl salt-sensitive rats (35). Hence the mutual binding sites of sGC subunits may present interesting targets for therapeutic interventions aimed at modulating basal as well as NO-driven cGMP production in vascular cells.…”

Identification and Characterization of a Novel β Subunit of Soluble Guanylyl Cyclase That Is Active in the Absence of a Second Subunit and Is Relatively Insensitive to Nitric Oxide

“…This reduced activity could reflect the formation of a less active heterodimer, although it could also be the result of reduced transfection efficiency. It is also interesting to note that although the rat ␤2 subunit will form heterodimers with ␣1 subunits, the ␣1/␤2 heterodimer shows lower NO-stimulated activity compared with the ␣1/␤1 heterodimers (31).…”

MsGC-β3 forms active homodimers and inactive heterodimers with NO-sensitive soluble guanylyl cyclase subunits

“…These data did not, however, indicate whether heterodimers were formed or had any basal enzyme activity. The mammalian β2 subunit acts in a dominant negative manner, forming heterodimers with the mammalian α1 subunit that are less sensitive to NO than the α1/β1 combination (Gupta et al, 1997). To determine whether MsGC-β3 behaved in a similar manner, we cotransfected COS-7 cells with all three subunits: MsGC-α1, MsGC-β1 and MsGC-β3 (Table 2).…”