The same mutation in Gsalpha and transducin alpha reveals behavioral differences between these highly homologous G protein alpha-subunits

Genotype-phenotype correlations in pseudohypoparathyroidism type 1a patients: a systemic review

BACKGROUND

Pseudohypoparathyroidism type 1a (PHP1a) is a rare endocrine disease caused by partial defects of the α subunit of the stimulatory Guanosin triphosphate (GTP) binding protein (Gsα) resulting from maternal GNAS gene variation. The clinical manifestations are related to PTH resistance (hypocalcemia, hyperphosphatemia, and elevated serum intact PTH) in the presence or absence of multihormone resistance, and Albright's hereditary osteodystrophy (AHO).

OBJECTIVES

To summarize the molecular genetics results and clinical characteristics as well as to explore the correlations between them.

METHODS

Articles pertaining to PHP1a until May, 31, 2021 were reviewed and 527 patients with genetic diagnosis were included in the data analysis. The clinical characteristics and molecular genetics results of these patients were analyzed and compared to explore the correlations between them.

RESULTS

A total of 258 GNAS rare variants (RVs) were identified in 527 patients. The RVs were most commonly found in exons 1 and 7 (17.6% each), with frameshift (36.8%), and missense (31.3%) being the main types of RVs. The median age of onset was 5.0 years old. The most common clinical manifestations were elevation of PTH (86.7%) and AHO (87.5%). Thyroid stimulating hormone resistance was the most common hormone resistance (75.5%) other than PTH resistance. Patients with missense and in-frame RVs had lower incidence rates of the round face (P = .001) and subcutaneous ossifications (P < .001) than those with loss-of-function (non-sense, frameshift, splicing site variants, and large deletions) variants.

CONCLUSIONS

This study revealed the correlation between loss-of-function RVs with round faces and subcutaneous ossifications in PHP 1a patients. Further exploration of genotype-phenotype correlations through more standardized and prospective studies with long-term follow-up is necessary.

Genome-wide meta-analyses of plasma renin activity and concentration reveal association with the kininogen 1 and prekallikrein genes

BACKGROUND

The renin-angiotensin-aldosterone system (RAAS) is critical for regulation of blood pressure and fluid balance and influences cardiovascular remodeling. Dysregulation of the RAAS contributes to cardiovascular and renal morbidity. The genetic architecture of circulating RAAS components is incompletely understood.

METHODS AND RESULTS

We meta-analyzed genome-wide association data for plasma renin activity (n=5275), plasma renin concentrations (n=8014), and circulating aldosterone (n=13289) from ≤4 population-based cohorts of European and European-American ancestry, and assessed replication of the top results in an independent sample (n=6487). Single-nucleotide polymorphisms (SNPs) in 2 independent loci displayed associations with plasma renin activity at genome-wide significance (P<5×10(-8)). A third locus was close to this threshold (rs4253311 in kallikrein B [KLKB1], P=5.5×10(-8)). Two of these loci replicated in an independent sample for both plasma renin and aldosterone concentrations (SNP rs5030062 in kininogen 1 [KNG1]: P=0.001 for plasma renin, P=0.024 for plasma aldosterone concentration; and rs4253311 with P<0.001 for both plasma renin and aldosterone concentration). SNPs in the NEBL gene reached genome-wide significance for plasma renin concentration in the discovery sample (top SNP rs3915911; P=8.81×10(-9)), but did not replicate (P=0.81). No locus reached genome-wide significance for aldosterone. SNPs rs5030062 and rs4253311 were not related to blood pressure or renal traits; in a companion study, variants in the kallikrein B locus were associated with B-type natriuretic peptide concentrations in blacks.

CONCLUSIONS

We identified 2 genetic loci (kininogen 1 and kallikrein B) influencing key components of the RAAS, consistent with the close interrelation between the kallikrein-kinin system and the RAAS.

Different biochemical properties explain why two equivalent Gα subunit mutants cause unrelated diseases

There is an increasing number of disease-associated Gα mutations identified from genome-wide sequencing campaigns or targeted efforts. Albright's Hereditary Osteodystrophy (AHO) was the first inherited disease associated with loss-of-function mutations in a G protein (Gαs) and other studies revealed gain-of-function Gα mutations in cancer. Here we attempted to solve the apparent quandary posed by the fact that the same mutation in two different G proteins appeared associated with both AHO and cancer. We first confirmed the presence of an inherited Gαs-R265H mutation from a previously described clinical case report of AHO. This mutation is structurally analogous to Gαo-R243H, an oncogenic mutant with increased activity in vitro and in cells due to rapid nucleotide exchange. We found that, contrary to Gαo-R243H, Gαs-R265H activity is compromised due to greatly impaired nucleotide binding in vitro and in cells. We obtained equivalent results when comparing another AHO mutation in Gαs (D173N) with a counterpart cancer mutation in Gαo (D151N). Gαo-R243H binds nucleotides efficiently under steady-state conditions but releases GDP much faster than the WT protein, suggesting diminished affinity for the nucleotide. These results indicate that the same disease-linked mutation in two different G proteins affects a common biochemical feature (nucleotide affinity) but to a different grade depending on the G protein (mild decrease for Gαo and severe for Gαs). We conclude that Gαs-R265H has dramatically impaired nucleotide affinity leading to the loss-of-function in AHO whereas Gαo-R243H has a mild decrease in nucleotide affinity that causes rapid nucleotide turnover and subsequent hyperactivity in cancer.

On the segregation of protein ionic residues by charge type

Based on ubiquitous presence of large ionic motifs and clusters in proteins involved in gene transcription and protein synthesis, we analyzed the distribution of ionizable sidechains in a broad selection of proteins with regulatory, metabolic, structural and adhesive functions, in agonist, antagonist, toxin and antimicrobial peptides, and in self-excising inteins and intron-derived proteins and sequence constructs. All tested groups, regardless of taxa or sequence size, show considerable segregation of ionizable sidechains into same type charge (homoionic) tracts. These segments in most cases exceed half of the sequence length and comprise more than two-thirds of all ionizable sidechains. This distribution of ionic residues apparently reflects a fundamental advantage of sorted electrostatic contacts in association of sequence elements within and between polypeptides, as well as in interaction with polynucleotides. While large ionic densities are encountered in highly interactive proteins, the average ionic density in most sets does not change appreciably with size of the homoionic segments, which supports the segregation as a modular feature favoring association.

Molecular basis of a novel oncogenic mutation in GNAO1

Heterotrimeric G proteins are molecular switches that control signal transduction, and their dysregulation can promote oncogenesis. Somatic mutations in GNAS, GNAI2 and GNAQ genes induce oncogenesis by rendering Gα subunits constitutively activated. Recently the first somatic mutation, arginine(243) → histidine (R243H) in the GNAO1 (Gαo) gene was identified in breast carcinomas and shown to promote oncogenic transformation when introduced into cells. Here, we provide the molecular basis for the oncogenic properties of the Gαo R243H mutant. Using limited proteolysis assays, nucleotide-binding assays, and single-turnover and steady-state GTPase assays, we demonstrate that the oncogenic R234H mutation renders Gαo constitutively active by accelerating the rate of nucleotide exchange; however, this mutation does not affect Gαo's ability to become deactivated by GTPase-activating proteins (GAPs) or by its intrinsic GTPase activity. This mechanism differs from that of previously reported oncogenic mutations that impair GTPase activity and GAP sensitivity without affecting nucleotide exchange. The constitutively active Gαo R243H mutant also enhances Src-STAT3 signaling in NIH-3T3 cells, a pathway previously shown to be directly triggered by active Gαo proteins to promote cellular transformation. Based on structural analyses, we propose that the enhanced rate of nucleotide exchange in Gαo R243H results from loss of the highly conserved electrostatic interaction of R243 with E43, located in the in the P-loop that represents the binding site for the α- and β-phosphates of the nucleotide. We conclude that the novel R234H mutation imparts oncogenic properties to Gαo by accelerating nucleotide exchange and rendering it constitutively active, thereby enhancing signaling pathways, for example, src-STAT3, responsible for neoplastic transformation.

Obligatory role in GTP hydrolysis for the amide carbonyl oxygen of the Mg(2+)-coordinating Thr of regulatory GTPases

When G-protein alpha subunits binds GTP and Mg(2+), they transition from their inactive to their active conformation. This transition is accompanied by completion of the coordination shell of Mg(2+) with electrons from six oxygens: two water molecules, the ss and gamma phosphoryls of GTP, a helix-alpha1 Ser, and a switch I domain (SWI) Thr, and the repositioning of SWI and SWII domains. SWII binds and regulates effector enzymes and facilitates GTP hydrolysis by repositioning the gamma-carbonyl of a Gln. Mutating the Ser generates regulatory GTPases that cannot lock Mg(2+) into its place and are locked in their inactive state with dominant negative properties. Curiously, mutating the Thr appears to reduce GTP hydrolysis. The reason for this difference is not known because it is also not known why removal of the Thr should affect the overall GTPase cycle differently than removal of the Ser. Working with recombinant Gsalpha, we report that mutating its SWI-Thr to either Ala, Glu, Gln, or Asp results not only in diminished GTPase activity but also in spontaneous activation of the SWII domain. Upon close examination of existing alpha subunit crystals, we noted the oxygen of the backbone carbonyl of SWI-Thr and of the gamma-carbonyl of SWII Gln to be roughly equidistant from the oxygen of the hydrolytic H(2)O. Our observations indicate that the Gln and Thr carbonyls play equihierarchical roles in the GTPase process and provide the mechanism that explains why mutating the Thr mimics mutating the Gln and not that of the Ser.