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Summary Objective Autosomal dominant hypocalcaemia or hypoparathyroidism is caused by activating mutations of the calcium-sensing receptor (CaSR). Treatment with calcium and vitamin D often worsens hypercalciuria and nephrocalcinosis, and renal impairment can result. Our aim was to describe the phenotypic variance of this rare disorder in a large series and to evaluate the outcome after long-term treatment. Design Nationwide retrospective collaborative study. Patients We describe 25 patients (14 men and 11 women), 20 belonging to 11 families and five single cases. Measurements Activating CaSR mutations and clinical and biochemical findings were evaluated. Results Nine different missense mutations of the CaSR, including one novel variant (M734T), were found. Twelve patients (50%) were symptomatic, 9 (36%) had basal ganglia calcifications and 3 (12%) had nephrocalcinosis. Serum calcium was decreased (1·87 ± 0·13 m m), and PTH was decreased ( n = 19) or inappropriately low ( n = 4). The occurrence of hypocalcaemic symptoms at diagnosis was related to the degree of hypocalcaemia. The occurrence of features like calcification of basal ganglia or kidney calcification did not correlate with the severity of hypocalcaemia or the age at diagnosis. The most common treatment was calcitriol (median dosage 0·6 μg/day), and the mean duration of therapy was 7·1 years (max. 26 years). Hypercalcaemic episodes rarely occurred, and the rate of kidney calcifications was remarkably low (12%). Conclusion This series increases the limited knowledge of mutations and phenotypes of this rare disorder. Mutation analysis of the CaSR gene facilitates patient and family management. Low dosages of calcitriol resulted in less frequent renal calcifications. [ABSTRACT FROM AUTHOR]

Primary hyperparathyroidism (HPT) is characterised by autonomous secretion of PTH from enlarged parathyroid glands leading, in most patients, to asymptomatic hypercalcaemia. Familial hypocalciuric hypercalcaemia (FHH) is an autosomal dominant disorder caused by inactivating mutations in the calcium-sensing receptor (CaSR) gene; it is characterised by lifelong and usually asymptomatic hypercalcaemia. Establishing the correct diagnosis is important because surgery can be curative in HPT, but ineffective in FHH. There is overlap in the diagnostic criteria for the two disorders and some patients carrying inactivating mutations in the CaSR gene, which is suggestive of FHH, also have HPT with hyperplastic parathyroid glands or adenomas. CaSR gene mutations were analysed and clinical and biochemical parameters evaluated in 139 consecutive outpatients presenting with hypercalcaemia and suspected of having HPT. Six different mutations of the CaSR gene were found in eight patients. In four patients, classical FHH was suspected based on clinical and biochemical results and was confirmed by the CaSR mutations. In the other four patients, HPT was diagnosed based on the biochemical profile or symptoms; in these four patients, the parathyroids were operated on and single adenomas were histologically confirmed. In all four patients, serum calcium decreased postoperatively; and in three patients, serum calcium normalised postoperatively. The CaSR mutations in these patients were R25X, E250K and Q926R. The coexistence of HPT and FHH in four of 139 patients suggests a pathogenetic role of CaSR mutations in HPT. Despite also having a CaSR mutation, these patients benefited from parathyroid surgery. [ABSTRACT FROM AUTHOR]

Objective It remains controversial if glucocorticoid replacement therapy impairs bone mineral density (BMD) in young patients with 21-hydroxylase deficiency. We aimed to analyze the impact of treatment variables, phenotype and genotype on BMD and bone metabolism in these patients. Design Cross-sectional study. Measurements Twenty-eight Caucasian patients with classical 21-hydroxylase deficiency (5–39 years). Clinical parameters, hormonal status, osteocalcin (OC), C-terminal telopeptide of type I collagen (CTX), genotype and lumbar BMD ( Z-scores) were assessed. Cumulative and mean hydrocortisone equivalent doses were calculated for the entire treatment period. Results Patients with severely reduced BMD Z-scores (≤–2·5 SD) had significantly higher mean/cumulative glucocorticoid doses compared to patients with moderately reduced ( P = 0·003/ P = 0·026) and normal Z-scores (> –1 SD) ( P = 0·005/ P = 0·011). Mean hydrocortisone equivalent doses > 20 mg/m2/day led to significantly lower lumbar BMD Z-scores (–2·16 ± 1·4 SD) vs. doses ≤ 20 mg/m2/day (–0·59 ± 1·25 SD) ( P = 0·008). BMD correlated negatively with mean/cumulative glucocorticoid doses and treatment duration. OC (86·45 ± 37·45 ng/ml) and CTX (1·45 ± 0·43 ng/ml) were significantly increased compared to an age- and sex-matched control group in patients with active growth; only CTX was slightly increased in patients who completed growth. Conclusions High cumulative and mean glucocorticoid doses negatively impact on BMD in children and young adults with classical 21-hydroxylase deficiency. Substitution therapy should be adapted particularly at this life period to prevent bone loss. [ABSTRACT FROM AUTHOR]

The role of the hinge region between the binding domain and the catalytic domain in dihydrolipoyl transacetylase (E2p) from Azotobacter vinelandii was addressed, by deletion mutagenesis. Mutated dihydrolipoyl transacetylase proteins were constructed with a deletion of 11 amino acids in the hinge region between the binding domain and the N-terminal part of the catalytic domain of E2p [E2p(pAPE1)] and with a further deletion of 9 amino acids into the N-terminal sequence protruding from the globular structure of the catalytic domain [E2ptpAPE2)] and found to take pan in the intratrimer interaction. Both proteins behaved as wild-type E2p with respect to catalytic activity and quaternary structure. The interaction of the peripheral components pyruvate dehydrogenase (E1p) and lipoamide dehydrogenase (E3) with the mutated E2p proteins was studied. E2p(pAPE1) assembles to a trimeric pyrovate dehydrogenase complex (PDC) with 15% decreased complex activity. No difference in affinity towards the peripheral components was detected. Upon binding of E3, E2p(pAPE2) dissociates into trimers and monomers. At saturation, two dimers of E3 were bound/E2p monomer instead of one dimer/E2p chain in trimeric wild-type E2p or E2p(pAPE1). The monomeric E2p species was catalytically inactive. Upon binding of excess Elp, some monomer formation of the E2p mutant took place. E1p however can prevent monomerization by E3. It is concluded that E1p is bound between two different E2p chains in the trimer. The substrates CoA and acetyl-CoA also prevent monomerization because they are bound by amino acid residues of two different E2p chains. In the presence of CoA no difference in affinity with respect to E1p and E3 binding was observed CoA (and acetyICoA) also prevent dissociation of the 24-subunit core structure of wild-type E2p when added before addition of E1p or E3. Therefore, it seems likely that in vivo A. vinelandii PDC is based on a 24-subunil E2p core, like Escherichia coli PDC. A functional difference between complexes based on a trimer or a 24-subunit core has not been observed. A role of the hinge region as a spacer to allow binding of E1p or E3 seems unlikely. The results are discussed on the basis of the three-dimensional structure of the catalytic domain. [ABSTRACT FROM AUTHOR]

Two unique restriction sites were introduced by site-directed mutagenesis at identical positions in the DNA encoding the dihydrolipoyltransacetylase (E2p) components of the pyruvate dehydrogenase complex from Azotobacter vinelandii and from Escherichia coli. In this manner each DNA chain could be cut into three parts, coding for the lipoyl domain, which consists of three lipoyl subdomains, the binding domain and the core-forming catalytic domain, respectively. Chimeric E2p components were constructed by exchanging the three domains between E2p from A. vinelandii and E. coli on gene level. The six chimeric E2p proteins were expressed and purified from E. coli TG2. All chimeras were catalytically active, 24-subunit E2p proteins. Interactions of the peripheral components E1p and E3 with the wild-type enzymes from A. vinelandii and E. coli and with the chimeric proteins were studied by gel-filtration experiments, analytical ultracentrifugation and reconstitution of the overall activity of the complex. A.vinelandii E3 interacts only with those chimeras that contain the A. vinelandii binding domain, whereas E. coli E3 interacts with all chimeras. Exchange of the lipoyl or catalytic domain did not influence the binding properties of E3. Recognition of E1p depends on the origin of both the binding domain and the catalytic domain. E. coli E1p interacts strongly with those chimeras in which both the binding domain and the catalytic domain were derived from E. coil E2p and weakly with chimeras that contained either the binding domain or the catalytic domain from E. coli E2p. No binding of E. coli E1p was observed when both domains were of A. vinelandii origin. A. vinelandii E1p recognizes E2p from A. vinelandii and E. coli, but strong interaction required that the binding and catalytic domain were of the same origin. Exchange of lipoyl domains had no effect on the binding properties of the El p component. These observations confirm previous conclusions, based on site-directed mutagenesis of A. vinelandii E2p [Schulze, E., Westphal, A. H., Boumans, H. and de Kok, A. (1991) Eur. J. Biochem. 202, 841-848], that the binding site for El p consists of amino acid residues derived from both the binding and the catalytic domain and extend these conclusions to E. coli E2p. Dissociation of the 24 subunit E2p core was only detected when the chimeric E2p proteins contained the catalytic domain from A. vinelandii E2p. Dissociation depends on the binding of peripheral components to the E1p-binding sites, pointing to differences in the inter-trimmer contacts between the E2p proteins from both species. Reconstitution of PDC activity depends on saturation by peripheral components under the conditions used and on recognition of the lipoyl domain by the respective active sites. All reconstituted complexes, based on chimeric E2p proteins, regain PDC activity ranging between 16-96% of the wild-type activity. It is concluded that E1p is highly specific with respect to recognition of the lipoyl domain, in contrast to E2p and E3. [ABSTRACT FROM AUTHOR]

Site-directed mutagenesis was performed in the protease-sensitive region, between the lipoyl and catalytic domains and in the catalytic domain, of the dihydrolipoyl transacetylase component (E2p) of the pyruvate dehydrogenase complex from Azotobacter vinelandii. The interaction of the mutated enzymes with the peripheral components pyruvate dehydrogenase (E1p) and lipoamide dehydrogenase (E3) was studied by gel filtration experiments, analytical ultracentrifugation and reconstitution of the pyruvate dehydrogenase complex. Upon binding of peripheral components, the 24-subunit core of A. vinelandii wild-type E2p dissociates into tetramers. Four E1p or E3 dimers can bind to a tetramer. Binding is mutually exclusive, resulting in an active complex containing one E3 and three E1p dimers. Large deletions of the protease-sensitive region of E2p resulted in a total loss of the E1p and E3 binding. A small deletion (Δ P361–R362) or the point mutation K367Q in the protease-sensitive region did not influence E3 binding, but affected E1p binding strongly, although with excess E1p almost complete reconstitution was reached. For E2p with the point mutation R416D in the N-terminal region of the catalytic domain only 16% overall activity could be measured in reconstituted complexes. This is due to a very weak E1p/E2p interaction, whereas the E3 binding was not affected. The point mutation R416D did not influence the catalytic activity of E2p, although a function for this residue in the formation of the active site was predicted from amino acid similarities with chloramphenicol acetyltransferase type III from Escherichia coli. Deletion of the complete Ala + Pro-rich sequence between the protease-sensitive region and the catalytic domain did not affect the enzymological properties of E2p, nor the affinity for E1p or E3. A further deletion of 20 N-terminal residues from the catalytic domain destroyed the E2p activity. From gel filtration experiments it was concluded that the quaternary structure was unaffected, as was E3 binding. E1p binding was lost and, in contrast to the wild-type enzyme, no dissociation of the core upon addition of E3 was observed. This mutant enzyme possesses, like E. coli E2p, six E3 binding sites and clearly shows that interaction of E3 or E1p with the E1p sites and dissociation are linked processes. It is concluded that the binding site for E3 is located on the N-terminal part of the protease-sensitive region. In contrast, the binding site for E1p consists of two regions, one located on the protease-sensitive region and one of the catalytic domain. These regions are separated by a flexible sequence of about 20 amino acids. [ABSTRACT FROM AUTHOR]

Partial sequences of the dihydrolipoyl transacetytase component (E2p) of the pyruvate dehydrogenase complex from Azotobacter vinelandii and Escherichia coli, containing the catalytic domain, were cloned in pUC plasmids and over-expressed in E. coli TG2. A high expression of a homogeneous protein was only detectable for E2p mutants consisting of the catalytic domain and the alanine-proline-rich sequence between a putative binding region for the peripheral components and the catalytic domain(apa-4). Most of the catalytic domain from A. vinelandii without the apa-4 sequence was degraded intracellularly, probably due to incorrect folding. Fusion proteins of six amino acids from β-galactosidase, the apa-4 region and the catalytic domains of ,4, vinelandii or E. coli E2p could be highly purified. Both catalytic domains were assembled in 24-subtmit structures with a molecular mass of approximately 670 kDa. The expression of catalytic domain from A. vinelandii E2p is more than twice as high as found for wild-type E2p. This can be explained by intracellular degradation of overexpressed wild-type E2p, whereas the catalytic domains are stable against proteolysis/n vivo and in vitro. The interaction of the peripheral components pyruvate dehydrogenase (E1p) and dihydrolipoamide dehydrogenase (E3) with the catalytic domains was studied, using gel filtration on Superose-6 and sedimentation velocity experiments. No binding of either E1p or E3 to the catalytic domain of either organism was detectable. Crystals of the catalytic domain of A. vinelandii E2p could ix: grown to a maximum size of 0.6 × 0.6 times; 0.4 mm. They diffract up to a resolution of 0.28 nm. [ABSTRACT FROM AUTHOR]

The interaction between lipoamide dehydrogenase (E3) and dihydrolipoyl transacetylase (E2p) from the pyruvate dehydrogenase complex was studied during the reconstitution of monomeric E3 apoenzymes from Azotobacter vinelandii and Pseudomonas fluorescens. The dimeric form of E3 is not only essential for catalysis but also for binding to the E2p core, because the apoenzymes as well as a monomeric holoenzyme from P. fluorescens, which can be stabilized as an intermediate at 0°C, do not bind to E2p. Lipoamide dehydrogenase from A. vinelandii contains a C-terminal extension of 15 amino acids with respect to glutathione reductase which is, in contrast to E3, presumably not part of a multienzyme complex. Furthermore, the last 10 amino acid residues of E3 are not visible in the electron density map of the crystal structure and are probably disordered. Therefore, the C-terminal tail of E3 might be an attractive candidate for a binding region. To probe this hypothesis, a set of deletions of this part was prepared by site-directed mutagenesis. Deletion of the last five amino acid residues did not result in significant changes. A further deletion of four amino acid residues resulted in a decrease of lipoamide activity to 5% of wild type, but the binding to E2p was unaffected. Therefore it is concluded that the C-terminus is not directly involved in binding to the E2p core. Deletion of the last 14 amino acids produced an enzyme with a high tendency to dissociate (Kd approximately 2.5 μM). This mutant binds only weakly to E2p. The diaphorase activity was still high. This indicates, together with the decreased Km for NADH, that the structure of the monomer is not appreciably changed by the mutation. Rather the orientation of the monomers with respect to each other is changed. It can be concluded that the binding region of E3 for E2p is constituted from structural parts of both monomers and binding occurs only when dimerization is complete. [ABSTRACT FROM AUTHOR]

The nucleotide sequence of the gene encoding the 2-oxoglutarate dehydrogenase component (Elo) of the 2- oxoglutarate dehydrogenase complex from Azotobacter vinelandii has been determined. The protein-coding se- quence consists of 2832 bp (944 codons, including the AUG start codon and the UAA stop codon). The predicted molecular mass (105687 Da) is in good agreement with that published for the isolated enzyme. The Elo gene is separated from the gene encoding the E2o component by a 42-bp intergenic region. No Escherichia-coli-like promoter sequences are found in the sequenced 97 bp upstream from the Elo gene. A putative ribosome-binding site is located 10–16 bp upstream from the start codon of the Elo gene. No terminator sequences could be detected downstream from the stop codon. Together with the identical situation for the E2o gene and the presence of terminating sequences downstream of the E3 gene, it can be assumed that all three genes of the 2-oxoglutarate dehydrogenase multienzyme complex are transcribed as a single mRNA transcript under the control of a promoter, located more than 100 bp upstream of the Elo gene, analogous to the pyruvate dehydrogenase complex in E. coli. The similarity with the sucA gene of E. coli is high with 59% identity. [ABSTRACT FROM AUTHOR]