Identification of an active site alanine in mevalonate kinase through characterization of a novel mutation in mevalonate kinase deficiency

Identification of FDA-approved drugs that increase mevalonate kinase in hyper IgD syndrome

Mevalonate kinase deficiency (MKD) is an autoinflammatory metabolic disorder caused by bi-allelic loss-of-function variants in the MVK gene, resulting in decreased activity of the encoded mevalonate kinase (MK). Clinical presentation ranges from the severe early-lethal mevalonic aciduria to the milder hyper-IgD syndrome (MKD-HIDS), and is in the majority of patients associated with recurrent inflammatory episodes with often unclear cause. Previous studies with MKD-HIDS patient cells indicated that increased temperature, as caused by fever during an inflammatory episode, lowers the residual MK activity, which causes a temporary shortage of non-sterol isoprenoids that promotes the further development of inflammation. Because an increase of the residual MK activity is expected to make MKD-HIDS patients less sensitive to developing inflammatory episodes, we established a cell-based screen that can be used to identify compounds and/or therapeutic targets that promote this increase. Using a reporter HeLa cell line that stably expresses the most common MKD-HIDS variant, MK-V377I, C-terminally tagged with bioluminescent NanoLuc luciferase (nLuc), we screened the Prestwick Chemical Library®, which includes 1280 FDA-approved compounds. Multiple compounds increased MK-V377I-nLuc bioluminescence, including steroids (i.e., glucocorticoids, estrogens, and progestogens), statins and antineoplastic drugs. The glucocorticoids increased MK-V377I-nLuc bioluminescence through glucocorticoid receptor signaling. Subsequent studies in MKD-HIDS patient cells showed that the potent glucocorticoid clobetasol propionate increases gene transcription of MVK and other genes regulated by the transcription factor sterol regulatory element-binding protein 2 (SREBP-2). Our results suggest that increasing the flux through the isoprenoid biosynthesis pathway by targeting the glucocorticoid receptor or SREBP-2 could be a potential therapeutic strategy in MKD-HIDS.

Twists and turns of the genetic story of mevalonate kinase-associated diseases: A review

Mevalonate kinase (MK)-associated diseases encompass a broad spectrum of rare auto-inflammatory conditions, all resulting from pathogenic variants in the mevalonate kinase gene (MVK). Their clinical manifestations are highly variable, ranging from more or less serious systemic disorders, such as hereditary recurrent fevers, to purely localized pathologies such as porokeratosis. The oldest condition identified as linked to this gene is a metabolic disease called mevalonic aciduria, and the most recent is disseminated superficial actinic porokeratosis, a disease limited to the skin. The modes of inheritance of MK-associated diseases also diverge among the different subtypes: recessive for the systemic subtypes and dominant with a post-zygotic somatic genetic alteration for MVK-associated porokeratosis. This review quickly retraces the historical steps that led to the description of the various MK-associated disease phenotypes and to a better understanding of their pathophysiology, then summarizes and compares the different genetic mechanisms involved in this group of disorders, and finally discusses the diverse causes that could underlie this phenotypic heterogeneity.

Phenotypic diversity, disease progression, and pathogenicity of MVK missense variants in mevalonic aciduria

Mevalonic aciduria (MVA) and hyperimmunoglobulinemia D syndrome (MKD/HIDS) are disorders of cholesterol biosynthesis caused by variants in the MVK gene and characterized by increased urinary excretion of mevalonic acid. So far, 30 MVA patients have been reported, suffering from recurrent febrile crises and neurologic impairment. Here, we present an in-depth analysis of the phenotypic spectrum of MVA and provide an in-silico pathogenicity model analysis of MVK missense variants. The phenotypic spectrum of 11 MVA patients (age range 0-51 years) registered in the Unified European Registry for Inherited Metabolic Disorders database was systematically analyzed using terms of the Human Phenotype Ontology. Biochemical, radiological as well as genetic characteristics were investigated. Six of eleven patients have reached adulthood and four have reached adolescence. One of the adolescent patients died at the age of 16 years and one patient died shortly after birth. Symptoms started within the first year of life, including episodic fever, developmental delay, ataxia, and ocular involvement. We also describe a case with absence of symptoms despite massive excretion of mevalonic acid. Pathogenic variants causing MVA cluster within highly conserved regions, which are involved in mevalonate and ATP binding. The phenotype of adult and adolescent MVA patients is more heterogeneous than previously assumed. Outcome varies from an asymptomatic course to early death. MVK variants cluster in functionally important and highly conserved protein domains and show high concordance regarding their expected pathogenicity.

Mevalonate Kinase-Associated Diseases: Hunting for Phenotype-Genotype Correlation

Mevalonate kinase-associated diseases (MKAD) are caused by pathogenic mutations in the mevalonate kinase gene (MVK) and encompass several phenotypically different rare and hereditary autoinflammatory conditions. The most serious is a recessive systemic metabolic disease called mevalonic aciduria, and the most recently recognized is disseminated superficial actinic porokeratosis, a dominant disease limited to the skin. To evaluate a possible correlation between genotypes and (1) the different MKAD clinical subtypes or (2) the occurrence of severe manifestations, data were reviewed for all patients with MVK variants described in the literature (N = 346), as well as those referred to our center (N = 51). The genotypes including p.(Val377Ile) (homozygous or compound heterozygous) were more frequent in mild systemic forms but were also sometimes encountered with severe disease. We confirmed that amyloidosis was more prevalent in patients compound heterozygous for p.(Ile268Thr) and p.(Val377Ile) than in others and revealed new associations. Patients homozygous for p.(Leu264Phe), p.(Ala334Thr) or compound heterozygous for p.(His20Pro) and p.(Ala334Thr) had increased risk of severe neurological or ocular symptoms. All patients homozygous for p.(Leu264Phe) had a cataract. The variants associated with porokeratosis were relatively specific and more frequently caused a frameshift than in patients with other clinical forms (26% vs. 6%). We provide practical recommendations focusing on phenotype-genotype correlation in MKAD that could be helpful for prophylactic management.

Hyper-IgD and periodic fever syndrome (HIDS) due to compound heterozygosity for G336S and V377I in a 44-year-old patient with a 27-year history of fever

Hereditary autoinflammatory syndromes are a rare, but notable cause of fever of unknown origin. During the last few years, the knowledge of the genetic background has significantly increased. Here, we report a novel pathogenic mutation in the MVK gene as the cause of fever in a 44-year-old male patient with a history of fever over a period of 27 years.

Mutations in the mevalonate kinase (MVK) gene cause nonsyndromic retinitis pigmentosa

OBJECTIVE

Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous disorder characterized by night blindness and peripheral vision loss, and in many cases leads to blindness. Despite extensive knowledge about genes involved in the pathogenesis of RP, the genetic cause remains elusive in many patients. In this study, we aimed to identify novel genes that are involved in the cause of RP.

DESIGN

We present a case series with mutations in the mevalonate kinase (MVK) gene.

PARTICIPANTS

A total of 769 patients with nonsyndromic RP and 174 Dutch control individuals participated in this study.

METHODS

Exome sequencing analysis was performed in a proband of Dutch origin who was initially diagnosed with nonsyndromic autosomal recessive RP. Mutations in MVK were identified and subsequently tested for segregation within the patient's family and screened in a large cohort of patients with genetically unsolved RP. Patients with mutations underwent extensive clinical reexamination.

MAIN OUTCOME MEASURES

Digital fundus photography, spectral-domain optical coherence tomography (OCT), and fundus autofluorescence analysis were performed in patients with MVK mutations. Mevalonate kinase (MK) enzyme activity was analyzed in cultured lymphoblastoid cells, and mevalonic acid levels were measured in urine samples.

RESULTS

Exome variant filtering and prioritization led to the identification of compound heterozygous mutations in MVK (p.I268T and p.A334T) in the proband and her affected brother. Screening of our nonsyndromic RP patient cohort revealed an additional individual who was homozygous for the p.A334T alteration. Clinical reevaluation of all 3 patients showed a classic form of RP with variable extraocular symptoms, such as history of recurrent childhood febrile crises in 2 patients, mild ataxia in 1, and renal failure in 1. All 3 affected individuals showed a significantly decreased MK activity and highly elevated levels of urinary mevalonic acid.

CONCLUSIONS

Although the MK activity in cells and mevalonic acid concentrations in urine are strongly aberrant and comparable to that in patients with systemic mevalonate kinase deficiency (MKD), only mild clinical symptoms related to this syndrome were observed in our patients. In the current article, we add another phenotype to the spectrum of diverging disorders associated with mutations in MVK.

Enzymes of the mevalonate pathway of isoprenoid biosynthesis

The mevalonate pathway accounts for conversion of acetyl-CoA to isopentenyl 5-diphosphate, the versatile precursor of polyisoprenoid metabolites and natural products. The pathway functions in most eukaryotes, archaea, and some eubacteria. Only recently has much of the functional and structural basis for this metabolism been reported. The biosynthetic acetoacetyl-CoA thiolase and HMG-CoA synthase reactions rely on key amino acids that are different but are situated in active sites that are similar throughout the family of initial condensation enzymes. Both bacterial and animal HMG-CoA reductases have been extensively studied and the contrasts between these proteins and their interactions with statin inhibitors defined. The conversion of mevalonic acid to isopentenyl 5-diphosphate involves three ATP-dependent phosphorylation reactions. While bacterial enzymes responsible for these three reactions share a common protein fold, animal enzymes differ in this respect as the recently reported structure of human phosphomevalonate kinase demonstrates. There are significant contrasts between observations on metabolite inhibition of mevalonate phosphorylation in bacteria and animals. The structural basis for these contrasts has also recently been reported. Alternatives to the phosphomevalonate kinase and mevalonate diphosphate decarboxylase reactions may exist in archaea. Thus, new details regarding isopentenyl diphosphate synthesis from acetyl-CoA continue to emerge.

Mutational spectrum and genotype–phenotype correlations in mevalonate kinase deficiency

Mevalonate kinase deficiency (MKD) is an autosomal recessive autoinflammatory disorder caused by mutations in the MVK gene resulting in deficient activity of mevalonate kinase (MK). Depending on the clinical severity, MKD may present as hyper-IgD and periodic fever syndrome (HIDS) or the more severe mevalonic aciduria (MA). We analyzed the MVK gene in 57 patients with MKD and found 39 different mutations including 15 novel mutations, expanding the total mutational spectrum of MKD to 63 mutations. To get more insight into the genotype-phenotype correlation in MKD, we studied the effect of selected missense mutations on MK protein stability and activity in various patient fibroblast cell lines. All MKD cell lines showed markedly decreased MK activities that correlated well with the clinical severity and, for most of the cell lines, with the amount of MK protein. When fibroblasts of MKD patients were cultured under conditions known to promote a more controlled protein folding, all cell lines of patients with the HIDS phenotype and few cell lines of patients with the MA phenotype showed an increase in the residual MK activity. This increase in enzyme activity correlates well with an increase in the MK protein levels in these cell lines, indicating that most of the mutations in MKD affect stability and/or folding of the MK protein rather than affecting the catalytic properties of the enzyme. The finding that the residual activity in MKD can be manipulated by environmental conditions may offer therapeutic options to alleviate or prevent the clinical symptoms associated with MKD.

Molecular functions of conserved aspects of the GHMP kinase family

The sequences and three-dimensional structures of the galactokinase, homoserine kinase, mevalonate kinase, and phosphomevalonate kinase (GHMP) family were compared to identify highly conserved surface residues. The functions of these solvent-accessible residues were assessed by determining the effects of their substitution, via mutagenesis, on the initial-rate parameters of a representative member of the GHMP kinase family, phosphomevalonate kinase from Streptococcus pneumoniae. What emerges from this study is a profile of the conserved surface-linked functions of the family. Certain substitutions produce highly selective effects on the steady-state affinity of a particular substrate, while one residue, Asp150, appears to be a pure k(cat) effector. Substitutions elsewhere affect multiple initial-rate parameters with varying, and sometimes compensatory, patterns. An alpha-helix that repositions during catalysis was substituted along its length to assess how its different segments contribute to catalysis-the substrate-proximal edge of the helix affects ATP recognition and k(cat), while the distal edge affects recognition of both substrates without affecting turnover. GHMP kinase mutations at the conserved surface residues corresponding to Ser291 and Ala293 in phosphomevalonate kinase are linked to mevalonic acid deficiency, which can lead to early fatality, and galactokinase deficiency, which causes cataracts. Our results suggest that the molecular basis for this particular galactokinase deficiency is an increase in the K(m) for galactose.

Isoprenoids: Remarkable diversity of form and function

The isoprenoid biosynthetic pathway is the source of a wide array of products. The pathway has been highly conserved throughout evolution, and isoprenoids are some of the most ancient biomolecules ever identified, playing key roles in many life forms. In this review we focus on C-10 mono-, C-15 sesqui-, and C-20 diterpenes. Evidence for interconversion between the pathway intermediates farnesyl pyrophosphate and geranylgeranyl pyrophosphate and their respective metabolites is examined. The diverse functions of these molecules are discussed in detail, including their ability to regulate expression of the beta-HMG-CoA reductase and Ras-related proteins. Additional topics include the mechanisms underlying the apoptotic effects of select isoprenoids, antiulcer activities, and the disposition and degradation of isoprenoids in the environment. Finally, the significance of pharmacological manipulation of the isoprenoid pathway and clinical correlations are discussed.

Enterococcus faecalis mevalonate kinase

Gram-positive pathogens synthesize isopentenyl diphosphate, the five-carbon precursor of isoprenoids, via the mevalonate pathway. The enzymes of this pathway are essential for the survival of these organisms, and thus may represent possible targets for drug design. To extend our investigation of the mevalonate pathway in Enterococcus faecalis, we PCR-amplified and cloned into pET-28b the mvaK1 gene thought to encode mevalonate kinase, the fourth enzyme of the pathway. Following transformation of the construct EFK1-pET28b into Escherichia coli BL21(DE3) cells, the expressed C-terminally hexahistidine-tagged protein was purified on a nickel affinity support to apparent homogeneity. The purified protein catalyzed the divalent ion-dependent phosphorylation of mevalonate to mevalonate 5-phosphate. The specific activity of the purified kinase was 24 micromole/min/mg protein. Based on sedimentation velocity data, E. faecalis mevalonate kinase exists in solution primarily as a monomer with a mass of 32.2 kD. Optimal activity occurred at pH 10 and at 37 degrees C. Delta H(a) was 22 kcal/mole. Kinetic analysis suggested that the reaction proceeds via a sequential mechanism. K(m) values were 0.33 mM (mevalonate), 1.1 mM (ATP), and 3.3 mM (Mg(2+)). Unlike mammalian mevalonate kinases, E. faecalis mevalonate kinase utilized all tested nucleoside triphosphates as phosphoryl donors. ADP, but not AMP, inhibited the reaction with a K(i) of 2.7 mM.

Regulation of isoprenoid/cholesterol biosynthesis in cells from mevalonate kinase-deficient patients

Mevalonic aciduria (MA) and hyper-IgD and periodic fever syndrome (HIDS) are two inherited disorders both caused by depressed mevalonate kinase (MK) activity. MK is the first enzyme to follow the highly regulated 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase (HMGR), which catalyzes the rate-limiting step in the isoprenoid/cholesterol biosynthesis pathway. In fibroblasts of MA patients, but not of HIDS patients, HMGR activity is elevated under normal growth conditions. This activity is down-regulated when cells are supplemented with the isoprenoid precursors geraniol, farnesol, and geranylgeraniol, and a mixture of 25-hydroxycholesterol and cholesterol. This indicates that the regulation of the pathway in these cells is not disturbed. The elevated HMGR activity is probably due to a shortage of non-sterol isoprenoid end products, as indicated by normal HMGR mRNA levels in MA fibroblasts. Furthermore, the HMGR activity in MA cells was more sensitive to geranylgeraniol suppression and less sensitive to sterol suppression than the HMGR activity in low density lipoprotein receptor-deficient cells. HMGR activity in MA cells was down-regulated also by addition of its product mevalonate to the culture medium. Thus, it appears that the elevation of mevalonate levels, which are high in MA patients and moderate in HIDS patients, allows the cells to compensate for the depressed MK activity. Indeed, the isoprenylation of Ras and RhoA protein appeared normal in HIDS and MA fibroblasts under normal conditions but showed increased sensitivity toward inhibition of HMGR by simvastatin. Our results indicate that MK-deficient cells maintain the flux through the isoprenoid/cholesterol biosynthesis pathway by elevating intracellular mevalonate levels.

Carrier frequency of the V377I (1129G>A) MVK mutation, associated with Hyper-IgD and periodic fever syndrome, in the Netherlands

Hyper-IgD and periodic fever syndrome (HIDS) and mevalonic aciduria (MA) are two autosomal recessive disorders that both are caused by a deficient activity of the enzyme mevalonate kinase (MK) due to mutations in the encoding gene (MVK). The most frequently occurring MVK mutation, V377I (1129G>A), has been identified exclusively in HIDS patients. Other common mutations have been associated with both HIDS and MA. To estimate the incidence of MK deficiency in the Netherlands, we determined the carrier frequency of the V377I mutation in genomic DNA extracted from anonymised newborn screening cards by PCR-RFLP. We found 14 carriers among 2138 analysed samples (1 : 153). Based on the V377I allele frequency of 42% in patients diagnosed with MK deficiency, the carrier frequency of any MVK mutation in the Dutch population can be calculated as 1 : 65. This predicts a disease incidence between 1 in 5196 and 1 in 53 656, which is far more than actually observed. Although under-diagnosis of patients with MK deficiency remains possible, this discrepancy probably is due to a reduced penetrance of V377I homozygosity. Analysis of the distribution of the V377I allele within patients carrying MVK mutations revealed that this was not according to the Hardy-Weinberg equilibrium principle, most probably due to an under-representation of V377I homozygotes in HIDS. Homozygotes for V377I might exhibit a much milder phenotype of MK deficiency or no disease-phenotype at all.

Mevalonate kinase deficiency: enlarging the clinical and biochemical spectrum

OBJECTIVE

Mevalonic aciduria as a result of mevalonate kinase deficiency is an inborn error of cholesterol biosynthesis characterized by dysmorphology, psychomotor retardation, progressive cerebellar ataxia, and recurrent febrile crises, usually manifesting in early infancy, accompanied by hepatosplenomegaly, lymphadenopathy, arthralgia, and skin rash. The febrile crises are similar to those observed in hyperimmunoglobulinemia D and periodic fever syndrome (HIDS). Pathogenic mutations in the mevalonate kinase gene in both disorders have demonstrated a common genetic basis. Our aim was to describe the clinical picture of adolescent patients with mevalonate kinase deficiency and to expand the clinical and biochemical spectrum of mevalonate kinase deficiency, particularly with regard to HIDS.

METHODS

We report the clinical history and biochemical findings of 3 patients with mevalonic aciduria.

RESULTS

In 2 siblings with mevalonic aciduria, a 15-year-old girl and a 14-year-old boy, the phenotype shifted with age. Ataxia has become the predominant clinical manifestation, whereas the febrile attacks occur less frequently but as yet have not disappeared. Both of them show marked elevations of immunoglobulin D (IgD). Psychomotor development is retarded but not regressive. Short stature developed in both patients. Additional findings include the development of retinal dystrophy and cataracts in both of them. The third patient is a 6-year-old boy who presented at the age of 5 years with cerebellar ataxia and retinal dystrophy. He is different from all known patients with mevalonic aciduria because of the mild neurologic involvement and because he has never developed febrile crises. In addition, levels of IgD were repeatedly normal.

CONCLUSION

The clinical and biochemical spectrum of patients with mevalonic aciduria is heterogeneous. Manifestations of the disease seem to be age dependent, as evident from this first report of adolescent patients. In patients who survive infancy, short stature, ataxia caused by cerebellar atrophy, and ocular involvement with retinal dystrophy become predominant findings. Recurrent febrile crises seem to diminish with increasing age and may not even be an obligatory finding. Elevation of IgD is most likely a secondary phenomenon that seems to be linked to recurrent febrile crises.

The structure of a binary complex between a mammalian mevalonate kinase and ATP: insights into the reaction mechanism and human inherited disease

Mevalonate kinase catalyzes the ATP-dependent phosphorylation of mevalonic acid to form mevalonate 5-phosphate, a key intermediate in the pathways of isoprenoids and sterols. Deficiency in mevalonate kinase activity has been linked to mevalonic aciduria and hyperimmunoglobulinemia D/periodic fever syndrome (HIDS). The crystal structure of rat mevalonate kinase in complex with MgATP has been determined at 2.4-A resolution. Each monomer of this dimeric protein is composed of two domains with its active site located at the domain interface. The enzyme-bound ATP adopts an anti conformation, in contrast to the syn conformation reported for Methanococcus jannaschii homoserine kinase. The Mg(2+) ion is coordinated to both beta- and gamma-phosphates of ATP and side chains of Glu(193) and Ser(146). Asp(204) is making a salt bridge with Lys(13), which in turn interacts with the gamma-phosphate. A model of mevalonic acid can be placed near the gamma-phosphoryl group of ATP; thus, the C5 hydroxyl is located within 4 A from Asp(204), Lys(13), and the gamma-phosphoryl of ATP. This arrangement of residues strongly suggests: 1) Asp(204) abstracts the proton from C5 hydroxyl of mevalonate; 2) the penta-coordinated gamma-phosphoryl group may be stabilized by Mg(2+), Lys(13), and Glu(193); and 3) Lys(13) is likely to influence the pK(a) of the C5 hydroxyl of the substrate. V377I and I268T are the most common mutations found in patients with HIDS. Val(377) is located over 18 A away from the active site and a conservative replacement with Ile is unlikely to yield an inactive or unstable protein. Ile-268 is located at the dimer interface, and its Thr substitution may disrupt dimer formation.

Structure of the Methanococcus jannaschii mevalonate kinase, a member of the GHMP kinase superfamily

The mevalonate-dependent pathway is used by many organisms to synthesize isopentenyl pyrophosphate, the building block for the biosynthesis of many biologically important compounds, including farnesyl pyrophosphate, dolichol, and many sterols. Mevalonate kinase (MVK) catalyzes a critical phosphoryl transfer step, producing mevalonate 5'-phosphate. The crystal structure of thermostable MVK from Methanococcus jannaschii has been determined at 2.4 A, revealing an overall fold similar to the homoserine kinase from M. jannaschii. In addition, the enzyme shows structural similarity with mevalonate 5-diphosphate decarboxylase and domain IV of elongation factor G. The active site of MVK is in the cleft between its N- and C-terminal domains. Several structural motifs conserved among species, including a phosphate-binding loop, have been found in this cavity. Asp(155), an invariant residue among MVK sequences, is located close to the putative phosphate-binding site and has been assumed to play the catalytic role. Analysis of the MVK model in the context of the other members of the GHMP kinase family offers the opportunity to understand both the mechanism of these enzymes and the structural details that may lead to the design of novel drugs.

Genetic disorders of cholesterol biosynthesis in mice and humans

Over the past few years, the number of identified inborn errors of cholesterol biosynthesis has increased significantly. The first inborn error of cholesterol biosynthesis to be characterized, in the mid 1980s, was mevalonic aciduria. In 1993, Irons et al. ( 1 ) (M. Irons, E. R. Elias, G. Salen, G. S. Tint, and A. K. Batta, Lancet 341:1414, 1993) reported that Smith-Lemli-Opitz syndrome, a classic autosomal recessive malformation syndrome, was due to an inborn error of cholesterol biosynthesis. This was the first inborn error of postsqualene cholesterol biosynthesis to be identified, and subsequently additional inborn errors of postsqualene cholesterol biosynthesis have been characterized to various extent. To date, eight inborn errors of cholesterol metabolism have been described in human patients or in mutant mice. The enzymatic steps impaired in these inborn errors of metabolism include mevolonate kinase (mevalonic aciduria as well as hyperimmunoglobulinemia D and periodic fever syndrome), squalene synthase (Ss-/- mouse), 3beta-hydroxysteroid Delta14-reductase (hydrops-ectopic calcification-moth-eaten skeletal dysplasia), 3beta-hydroxysteroid dehydrogenase (CHILD syndrome, bare patches mouse, and striated mouse), 3beta-hydroxysteroid Delta8,Delta7-isomerase (X-linked dominant chondrodysplasia punctata type 2, CHILD syndrome, and tattered mouse), 3beta-hydroxysteroid Delta24-reductase (desmosterolosis) and 3beta-hydroxysteroid Delta7-reductase (RSH/Smith-Lemli-Opitz syndrome and Dhcr7-/- mouse). Identification of the genetic and biochemical defects which give rise to these syndromes has provided the first step in understanding the pathophysiological processes which underlie these malformation syndromes.

Periodic fever syndromes

The term periodic fever syndrome has been used in a restricted sense to denote two diseases in which episodic fevers occur with a regular periodicity: cyclic neutropenia and the periodic fever, aphthous stomatitis, pharyngitis, and adenopathy (PFAPA) syndrome. Other authors have used the term in a more general sense to encompass a larger group of disorders characterized by recurrent episodes of fever that do not necessarily follow a strictly periodic pattern. These include familial Mediterranean fever, the autosomal dominant familial fevers (also known as Hibernian fever), and the hyperimmunoglobulin D syndrome. This article follows the latter usage, and reviews recent advances in our understanding of the genetics and molecular pathology of this group of diseases, as well as their clinical characterization and treatment.

Purification and characterization of mevalonate kinase from suspension-cultured cells of Catharanthus roseus (L.) G. Don

Mevalonate kinase was purified to homogeneity from Catharanthus roseus (L.) G. Don suspension-cultured cells. The purified enzyme had an M(r) of 104,600 and a subunit size of about 41,500. Kinetic studies indicated an ordered sequential mechanism of action, in which mevalonate was the first substrate to bind and ADP was the last product to leave the enzyme. True values for the kinetic constants were determined for mevalonate, with K(ma) = 76 microM and K(ia) = 74 microM, and for ATP, with K(mb) = 0.13 mM and K(ib) = 0. 13 mM; the true V(max) was calculated to be 138.7 nkat/mg of protein. Product inhibition was only detectable at rather high concentrations: above 0.7 mM for 5-phosphomevalonate and above 2 mM for ADP, with an ADP/ATP ratio of at least 1. Mevalonate kinase activity was shown to be strongly inhibited by farnesyl diphosphate. Farnesyl diphosphate acted as a competitive inhibitor toward ATP, with a K(i) value of 0.1 microM. Mevalonate kinase activity was dependent on the presence of divalent ions. At a concentration of 2 mM, Mg(2+) and Mn(2+) were best and equally effective in sustaining activity; compared to Mg(2+) and Mn(2+), relative activities of 35, 30, 16, 4.8, and 3.4% were detected at equimolar concentrations of Zn(2+), Fe(2+), Co(2+), Ca(2+), and Ni(2+), respectively. The pH-dependent activity profile of mevalonate kinase showed a broad pH optimum between pH 7 and 10, with a maximum at about pH 8.9.

Overexpression, purification, and characterization of the thermostable mevalonate kinase from Methanococcus jannaschii

We report here the first overexpression and characterization of a thermostable mevalonate kinase from an archae, Methanococcus jannaschii, a strict anaerobe, which produces methane and grows at pressure of 200 atm and an optimum temperature near 85 degrees C. PCR-derived DNA fragments containing the structural gene for mevalonate kinase were cloned into an expression vector, pET28a, to form pETMVK. The mevalonate kinase was overexpressed from Escherichia coli pETMVK/BL21(DE3) (15-20% of total soluble protein) when induced with isopropyl beta-d-thiogalactopyranoside. The protein was purified by heat treatment (to denature E. coli proteins), followed by metal-affinity chromatography on Talon metal-affinity resin column. The purified protein had a dimeric structure composed of identical subunits, and the M(r) of the enzyme determined by gel chromatography was 68K. Based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the subunit M(r) was 36, 000. The pI for mevalonate kinase was 7.8. The Michaelis constant (K(m)) for (RS)-mevalonate was 68.5 microM and was 92 microM for ATP. The V(max) was 387 units mg(-1). The optimal temperature for mevalonate kinase activity was 70-75 degrees C.

Identification and characterization of three novel missense mutations in mevalonate kinase cDNA causing mevalonic aciduria, a disorder of isoprene biosynthesis

Mevalonic aciduria is a rare autosomal recessive metabolic disorder, characterized by psychomotor retardation, failure to thrive, hepatosplenomegaly, anemia and recurrent febrile crises. The disorder is caused by a deficient activity of mevalonate kinase due to mutations in the encoding gene. Thus far, only two disease-causing mutations have been identified. We now report four different missense mutations including three novel ones, which were identified by sequence analysis of mevalonate kinase cDNA from three mevalonic aciduria patients. All mutations affect conserved amino acids. Heterologous expression of the corresponding mutant mevalonate kinases as fusion proteins with glutathione S -transferase in Escherichia coli showed a profound effect of each of the mutations on enzyme activity. In addition, immunoblot analysis of fibroblast lysates from patients using specific antibodies against mevalonate kinase identified virtually no protein. These results demonstrate that the mutations affect not only the activity but also the stability of the mutant proteins.

Identification of a mutation cluster in mevalonate kinase deficiency, including a new mutation in a patient of Mennonite ancestry

Mevalonate kinase (MKase) deficiency (MKD) is a rare autosomal recessive disorder in the pathway of cholesterol and nonsterol isoprenoid biosynthesis. Thus far, two disease-causing missense alleles have been identified, N301T and A334T. We report four additional mutations associated with MKD: L264F, T243I, L265P, and I268T, the last found in a patient of Mennonite ancestry. Electrophoretic analysis of bacterially expressed wild-type and mutant MKase indicated that I268T and T243I mutants produced normal or somewhat reduced amounts of MKase protein; conversely, L264F and L265P mutations resulted in considerably decreased, or absent, MKase protein. Immunoblot analysis of MKase from all patients suggested that the MKase polypeptide was grossly intact and produced in amounts comparable to control levels. Three mutations resulted in significantly diminished MKase enzyme activity (<2%), whereas the I268T allele yielded approximately 20% residual enzyme activity. Our results should allow more-accurate identification of carriers and indicate a mutation "cluster" within amino acids 240-270 of the mature MKase polypeptide.

Mutations in MVK, encoding mevalonate kinase, cause hyperimmunoglobulinaemia D and periodic fever syndrome

Hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS; MIM 260920) is an autosomal recessive disorder characterized by recurrent episodes of fever associated with lymphadenopathy, arthralgia, gastrointestinal dismay and skin rash. Diagnostic hallmark of HIDS is a constitutively elevated level of serum immunoglobulin D (IgD), although patients have been reported with normal IgD levels. To determine the underlying defect in HIDS, we analysed urine of several patients and discovered increased concentrations of mevalonic acid during severe episodes of fever, but not between crises. Subsequent analysis of cells from four unrelated HIDS patients revealed reduced activities of mevalonate kinase (MK; encoded by the gene MVK), a key enzyme of isoprenoid biosynthesis. Sequence analysis of MVK cDNA from the patients identified three different mutations, one of which was common to all patients. Expression of the mutant cDNAs in Escherichia coli showed that all three mutations affect the activity of the encoded proteins. Moreover, immunoblot analysis demonstrated a deficiency of MK protein in patient fibroblasts, indicating a protein-destabilizing effect of the mutations.

Characterization of the mevalonate kinase 5'-untranslated region provides evidence for coordinate regulation of cholesterol biosynthesis

Using a probe derived from the 5'-untranslated region of the human mevalonate kinase (MK) cDNA, we screened a lambda gt 11 genomic library and obtained a single clone containing the 5' untranslated region of the gene. Nucleotide sequencing identified several putative regulatory elements, including two Sp1 (GC box) elements and a CCAAT box. A canonical TATA box was not detected. Directly adjacent to one Sp1 element was a sterol regulatory element (SRE), 5'-CACCCCAG-3', which was a 7/8 base pair match to the consensus sequences identified in the genes encoding 3-hydroxy-3-methyl-glutaryl-coenzyme A synthase and reductase, and the LDL receptor. There was no Sp1 element upstream of the SRE. Northern blot analysis in human CRL1508T cells revealed that quantities of MK poly A+ RNA increased for cells grown in the presence of lipid-deficient calf serum, and further increased upon addition of 1 microM lovastatin. Primer extension analysis with human poly A+ RNA suggested at least 4 transcription initiation sites downstream from the CCAAT box. To assess sterol responsiveness of transcription initiation, a 1.4 kb genomic fragment upstream of the translational start site was fused to the pSV2cat vector for transient expression in COS-7 cells, with chloramphenicol acetyltransferase (CAT) as the reporter gene. This construct demonstrated modest levels of CAT expression which was induced > 2-fold when cells were grown in lipoprotein-deficient calf serum. Our data provide further evidence for coordinate regulation of cholesterol biosynthesis in response to sterol.