Heterozygous gain of function variant in GUCY1A2 may cause autonomous ovarian hyperfunction.

PURPOSE: The purpose of this study was to characterize the phenotype associated with a de novo gain-of-function variant in the GUCY1A2 gene. METHODS: An individual carrying the de novo heterozygous variant c.1458G>T p.(E486D) in GUCY1A2 was identified by exome sequencing. The effect of the corresponding enzyme variant α2E486D/ß1 was evaluated using concentration-response measurements with wild-type enzyme and the variant in cytosolic fractions of HEK293 cells, UV-vis absorbance spectra of the corresponding purified enzymes, and examination of overexpressed fluorescent protein-tagged constructs by confocal laser scanning microscopy. RESULTS: The patient presented with precocious peripheral puberty resembling the autonomous ovarian puberty seen in McCune-Albright syndrome. Additionally, the patient displayed severe intellectual disability. In vitro activity assays revealed an increased nitric oxide affinity for the mutant enzyme. The response to carbon monoxide was unchanged, while thermostability was decreased compared to wild type. Heme content, susceptibility to oxidation, and subcellular localization upon overexpression were unchanged. CONCLUSION: Our data define a syndromic autonomous ovarian puberty likely due to the activating allele p.(E486D) in GUCY1A2 leading to an increase in cGMP. The overlap with the ovarian symptoms of McCune-Albright syndrome suggests an impact of this cGMP increase on the cAMP pathway in the ovary. Additional cases will be needed to ensure a causal link.

Tyrosine 135 of the ß1 subunit as binding site of BAY-543: Importance of the Y-x-S-x-R motif for binding and activation by sGC activator drugs.

Soluble guanylyl cyclase (sGC), the major receptor for nitric oxide (NO), is a heterodimer consisting of two subunits, the α and the ß subunit. The NO/sGC/cGMP signaling pathway is protective in different disease pathomechanisms including angina pectoris, pulmonary hypertension and fibrotic diseases. The natural ligand heme has two carboxylic acids which interact in the ß1 heme nitric oxide oxygen binding (HNOX) domain with the amino acids of the highly conserved Y-x-S-x-R motif. The Y-x-S-x-R motif is also involved in binding of the dicarboxylic activators cinaciguat and BAY 60-2770 as indicated by crystallization studies of sGC activator and bacterial HNOX homologs. To what extent the Y-x-S-x-R motif hydrogen bond network contributes to binding of monocarboxylic acids has not been examined so far. In the current paper, the chemical structural formula of the novel monocarboxylic drug BAY-543 is described for the first time. Using this novel drug, we evaluate the importance of the amino acids Y135 and R139 for thermostabilization and activation in comparison to the dicarboxylic acid BAY 60-2770. Measurements with point mutated sGC variants demonstrate tyrosine 135 as exclusive binding site of the monocarboxylic acid BAY-543 but not the dicarboxylic BAY 60-2770.

Thermal shift assay: Strengths and weaknesses of the method to investigate the ligand-induced thermostabilization of soluble guanylyl cyclase.

Thermal shift assay is a fluorescence dye based biochemical method to determine the melting point of a protein. It can be used to investigate the ligand-induced stabilization of proteins and helps to increase the likelihood of crystallization in biological samples. Dimeric proteins like soluble guanylyl cyclase (sGC) have specific structural and functional properties which may pose a challenge in thermal shift measurements. In this paper, thermal shift assay was used to examine ligand-induced thermostabilization of the dimeric heme-containing protein soluble guanylyl cyclase. Adjustment of the parameters buffer solution, pH, protein / dye ratio and protein amount per well yielded a one-phase melting curve of sGC with a sharp transition and high reproducibility. We found that thermal shift measurement is not affected by heme state or heme content of the enzyme preparation. We used the method to investigate the thermostabilization of sGC induced by the heme-mimetic activator drugs cinaciguat, BAY 60-2770 and BR 11257 in combination with non-hydrolyzable nucleotides. Measurements with the dicarboxylic drugs cinaciguat and BAY 60-2770 yielded steep melting curves with high amplitudes. In contrast, in the presence of the monocarboxylic sGC activator BR 11257, melting curves appear flattened in the dye-based measurements. In the present paper, we show that activity-based thermostability measurements are superior to dye-based measurements in detecting the thermostabilizing influence of sGC activator drugs.

A novel soluble guanylyl cyclase activator, BR 11257, acts as a non-stabilising partial agonist of sGC.

The soluble guanylyl cyclase (sGC) plays a key role in NO/cGMP signalling and is widely recognised to be important in different disease pathomechanisms. The discovery of sGC agonists provides a new opportunity to stimulate the NO/cGMP pathway. One class of compounds are the heme-independent sGC activators, which are thought to bind to oxidised or heme-free sGC. This enzyme is preferentially formed under disease situations accompanied by oxidative stress. Accordingly, this binding mode of sGC activators has quite some appeal for the clinical use of sGC activator drugs in diseases with high oxidative stress burden. However, none of the previous sGC activators, most of them dicarboxylic acid derivatives, has passed clinical trials to date, also because of the potent blood pressure lowering effects. In the current study, we investigate the effects of a new monocarboxylic drug BR 11257 in vitro and in vivo. Activity measurements with purified enzyme indicated gentle sGC activation for BR 11257 resembling a partial agonistic behaviour. In thermal shift measurements, we observed an unexpected difference between BR 11257 and the sGC activators from the dicarboxylic acid type. While activators from the dicarboxylic acid type had a highly thermostabilising influence on sGC, this effect was absent with BR 11257. We hypothesize that the key interaction partner for thermostabilisation is the second carboxylic acid in BAY 60-2770 which is missing in BR 11257. The absence of this thermodynamic receptor stabilisation and the partial agonism may be advantageous to overcome limitations of this class of drugs by avoiding excessive hypotension.