Enzymatic and metabolic characterization of the phosphoglycerate kinase deficiency associated with chronic hemolytic anemia caused by the PGK-Barcelona mutation

Recognition of a novel variant of phosphoglycerate kinase 1 deficiency PGK1 Galveston (c.472G > C) in a child with hemolytic anemia, neurologic dysfunction and myopathy

The enzyme phosphoglycerate kinase 1 (PGK1) catalyzes the first ATP producing reaction in the glycolysis pathway. Certain mutations to the coding gene of PGK1 present clinically with varying manifestations including hemolytic anemia, central nervous system (CNS) dysfunction and myopathy. Various PGK1 mutations have been described in the literature at the clinical and molecular level. Herein, we describe a novel case PGK1 mutation (PGK1 Galveston) in a 4-year-old boy who presented with all three manifestations. We discuss the characteristic hematopathology findings from this patient as well as provide a comparison with previously described neuroimaging findings. The variable clinical presentation of this condition along with its inherent uniqueness provide a diagnostic challenge for physicians. This presentation will add to the current body of knowledge for this condition and help guide future investigation and management.

A Novel Missense Variant Associated with A Splicing Defect in A Myopathic Form of PGK1 Deficiency in The Spanish Population

Phosphoglycerate kinase (PGK)1 deficiency is an X-linked inherited disease associated with different clinical presentations, sometimes as myopathic affectation without hemolytic anemia. We present a 40-year-old male with a mild psychomotor delay and mild mental retardation, who developed progressive exercise intolerance, cramps and sporadic episodes of rhabdomyolysis but no hematological features. A genetic study was carried out by a next-generation sequencing (NGS) panel of 32 genes associated with inherited metabolic myopathies. We identified a missense variant in the PGK1 gene c.1114G > A (p.Gly372Ser) located in the last nucleotide of exon 9. cDNA studies demonstrated abnormalities in mRNA splicing because this change abolishes the exon 9 donor site. This novel variant is the first variant associated with a myopathic form of PGK1 deficiency in the Spanish population.

Identification of a novel variant in phosphoglycerate kinase-1 (PGK1) in an African-American child (PGK1 Detroit)

The human phosphoglycerate kinase-1 enzyme is the first of two energy generating steps in the glycolysis. Since its discovery in 1968, many pathologically mutated forms of PGK1 have been described. PGK1 is expressed in all tissues. The clinical manifestations of PGK1 deficiency are some combination of anemia, central nervous system and/or musculoskeletal manifestations. We describe a case of PGK1 in an African-American child, which to our knowledge, has never been described to date. The manifestations of PGK1-Detroit (c.1105A > C (p.Thr369Pro)) include hematologic and central nervous manifestations.

A novel PGK1 mutation associated with neurological dysfunction and the absence of episodes of hemolytic anemia or myoglobinuria

Phosphoglycerate kinase (PGK) deficiency affects three different organs: red blood cells (RBC), the central nervous system, and muscles. Next-generation sequencing identified a hemizygous PGK1 mutation (p.V217I) in a 16-year-old Japanese male patient presenting with intellectual disability and episodes of muscle weakness of unknown etiology. Enzymatic analysis demonstrated slightly lower RBC-PGK activity and compensatory increases of other glycolysis enzymes. This is the first PGK1 mutation found through next-generation sequencing.

Insulin and mTOR Pathway Regulate HDAC3-Mediated Deacetylation and Activation of PGK1

Phosphoglycerate kinase 1 (PGK1) catalyzes the reversible transfer of a phosphoryl group from 1, 3-bisphosphoglycerate (1, 3-BPG) to ADP, producing 3-phosphoglycerate (3-PG) and ATP. PGK1 plays a key role in coordinating glycolytic energy production with one-carbon metabolism, serine biosynthesis, and cellular redox regulation. Here, we report that PGK1 is acetylated at lysine 220 (K220), which inhibits PGK1 activity by disrupting the binding with its substrate, ADP. We have identified KAT9 and HDAC3 as the potential acetyltransferase and deacetylase, respectively, for PGK1. Insulin promotes K220 deacetylation to stimulate PGK1 activity. We show that the PI3K/AKT/mTOR pathway regulates HDAC3 S424 phosphorylation, which promotes HDAC3-PGK1 interaction and PGK1 K220 deacetylation. Our study uncovers a previously unknown mechanism for the insulin and mTOR pathway in regulation of glycolytic ATP production and cellular redox potential via HDAC3-mediated PGK1 deacetylation.

Cloning, expression and enzymatic characterization of 3-phosphoglycerate kinase from Schistosoma japonicum

In the present study, a full-length cDNA encoding the Schistosoma japonicum 3-phosphoglycerate kinase (SjPGK) with an open reading frame of 1251 bp was isolated from 42-day-old (42-d) schistosome cDNAs. Real-time quantitative reverse transcription PCR analysis revealed that SjPGK was expressed in all investigated developmental stages and at a higher transcript levels in 21- and 42-d worms. Moreover, the SjPGK mRNA level was significantly downregulated in 10-d schistosomula from Wistar rats (non-susceptible host). SjPGK was subcloned into pET28a(+) and expressed as both supernatant and inclusion bodies in Escherichia coli BL21 cells. The enzymatic activity of recombinant SjPGK protein (rSjPGK) was 125 U/mg. Kinetic analyses with respect to 3-phosphoglycerate (3-PGA) as substrate gave a Km of 2.69 mmol/L and a Vmax of 748 μmol/min/mg protein. rSjPGK was highly stable over a range of pH 8.0-9.0 and temperature of 30°C-40 °C under physiological conditions. Immunolocalization analysis showed that SjPGK was mainly distributed in the tegument and parenchyma of schistosomes. Western blotting showed that rSjPGK had good immunogenicity. We vaccinated BALB/c mice with rSjPGK combined with Seppic 206 adjuvant. However, there were no significant reductions in the numbers of worms of eggs in the liver, as compared to adjuvant or blank control groups in two independent vaccination tests. This study provides the basis for further investigations into the biological function of SjPGK, although it might not be suitable as a potential vaccine candidate against schistosomiasis.

Structural and energetic basis of protein kinetic destabilization in human phosphoglycerate kinase 1 deficiency

Protein kinetic destabilization is a common feature of many human genetic diseases. Human phosphoglycerate kinase 1 (PGK1) deficiency is a rare genetic disease caused by mutations in the PGK1 protein, which often shows reduced kinetic stability. In this work, we have performed an in-depth characterization of the thermal stability of the wild type and four disease-causing mutants (I47N, L89P, E252A, and T378P) of human PGK1. PGK1 thermal denaturation is a process under kinetic control, and it is described well by a two-state irreversible denaturation model. Kinetic analysis of differential scanning calorimetry profiles shows that the disease-causing mutations decrease PGK1 kinetic stability from ~5-fold (E252A) to ~100000-fold (L89P) compared to that of wild-type PGK1, and in some cases, mutant enzymes are denatured on a time scale of a few minutes at physiological temperature. We show that changes in protein kinetic stability are associated with large differences in enthalpic and entropic contributions to denaturation free energy barriers. It is also shown that the denaturation transition state becomes more nativelike in terms of solvent exposure as the protein is destabilized by mutations (Hammond effect). Unfolding experiments with urea further suggest a scenario in which the thermodynamic stability of PGK1 at least partly determines its kinetic stability. ATP and ADP kinetically stabilize PGK1 enzymes, and kinetic stabilization is nucleotide- and mutant-selective. Overall, our data provide insight into the structural and energetic basis underlying the low kinetic stability displayed by some mutants causing human PGK1 deficiency, which may have important implications for the development of native state kinetic stabilizers for the treatment of this disease.

A new variant of phosphoglycerate kinase deficiency (p.I371K) with multiple tissue involvement: molecular and functional characterization

Phosphoglycerate kinase (PGK) is a key glycolytic enzyme that catalyzes the reversible phosphotransfer reaction from 1,3-bisphosphoglycerate to MgADP, to form 3-phosphoglycerate and MgATP. Two isozymes encoded by distinct genes are present in humans: PGK-1, located on Xq-13.3, encodes a ubiquitous protein of 417 amino acids, whereas PGK-2 is testis-specific. PGK1 deficiency is characterized by mild to severe hemolytic anemia, neurological dysfunctions and myopathy; patients rarely exhibit all three clinical features. Nearly 40 cases have been reported, 27 of them characterized at DNA or protein level, and 20 different mutations were described. Here we report the first Italian case of PGK deficiency characterized at a molecular and biochemical level. The patient presented during infancy with hemolytic anemia, increased CPK values, and respiratory distress; the study of red blood cell enzymes showed a drastic reduction in PGK activity. In adulthood he displayed mild hemolytic anemia, mental retardation and severe myopathy. PGK-1 gene sequencing revealed the new missense mutation c.1112T>A (p.Ile371Lys). The mutation was not found among 100 normal alleles, and even if located in the third to the last nucleotide of exon 9, it did not alter mRNA splicing. The p.Ile371Lys mutation falls in a conserved region of the enzyme, near the nucleotide binding site. The mutant enzyme shows reduced catalytic rates toward both substrates (apparent k(cat) values, 12-fold lower than wild-type) and a decreased affinity toward MgATP (apparent K(m), 6-fold higher than wild-type). Moreover, it lost half of activity after nearly 9-min incubation at 45°C, a temperature that did not affect the wild-type enzyme (t(1/2)>1 h). The possible compensatory expression of PGK2 isoenzyme was investigated in the proband and in the heterozygote healthy sisters, and found to be absent. Therefore, the highly perturbed catalytic properties of the new variant p.Ile371Lys, combined with protein instability, account for the PGK deficiency found in the patient and correlate with the clinical expression of the disease.

Molecular insights on pathogenic effects of mutations causing phosphoglycerate kinase deficiency

Phosphoglycerate kinase (PGK) catalyzes an important ATP-generating step in glycolysis. PGK1 deficiency is an uncommon X-linked inherited disorder, generally characterized by various combinations of non-spherocytic hemolytic anemia, neurological dysfunctions, and myopathies. Patients rarely exhibit all three clinical features. To provide a molecular framework to the different pathological manifestations, all known mutations were reviewed and 16 mutant enzymes, obtained as recombinant forms, were functionally and structurally characterized. Most mutations heavily affect thermal stability and to a different extent catalytic efficiency, in line with the remarkably low PGK activity clinically observed in the patients. Mutations grossly impairing protein stability, but moderately affecting kinetic properties (p.I47N, p.L89P, p.C316R, p.S320N, and p.A354P) present the most homogeneous correlation with the clinical phenotype. Patients carrying these mutations display hemolytic anemia and neurological disorders, and,except for p.A354P variant, no myopaty. Variants highly perturbed in both catalytic efficiency (p.G158V, p.D164V, p.K191del, D285V, p.D315N, and p.T378P) and heat stability (all, but p.T378P) result to be mainly associated with myopathy alone. Finally, mutations faintly affecting molecular properties (p.R206P, p.E252A, p.I253T, p.V266M, and p.D268N) correlate with a wide spectrum of clinical symptoms. These are the first studies that correlate the clinical symptoms with the molecular properties of the mutant enzymes. All findings indicate that the different clinical manifestations associated with PGK1 deficiency chiefly depend on the distinctive type of perturbations caused by mutations in the PGK1 gene, highlighting the need for determination of the molecular properties of PGK variants to assist in prognosis and genetic counseling. However, the clinical symptoms can not be understood only on the bases of molecular properties of the mutant enzyme. Different (environmental, metabolic, genetic and/or epigenetic) intervening factors can contribute toward the expression of PGK deficient clinical phenotypes.