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T V McCarthy

Publications and source records attributed to T V McCarthy.

At least 19 recordsLinked to original sources
PubMed2005

Atypical L-type channels are down-regulated in hypoxia.

One type of cellular response to hypoxia is an increase in cytosolic Ca2+. VDCCs (voltage-dependent calcium channels) open upon membrane depolarization allowing inward current of Ca2+ ions. Two of the so-called L-type VDCC alpha1 subunits, Ca(v)1.2 and Ca(v)1.3, are found in the brain. We sought to investigate the effect of chronic hypoxia or treatment with a hypoxia-mimicking agent DFX (desferrioxamine mesylate) on expression of L-type VDCC in the SH-SY5Y neuroblastoma cell line. Western blotting identified two atypical forms of the L-type channel with apparent molecular masses of approx. 100 and 150 kDa, compared with typical forms of approx. 200 kDa. Immunofluorescence microscopy shows the approx. 100 kDa protein located within the cell and on the cell surface, while the approx. 150 kDa protein is intracellular with punctate staining. Further analysis revealed that this approx. 150 kDa protein co-localizes with nuclear proteins but not with markers for other intracellular compartments. In addition, these proteins are both down-regulated in DFX-treated and hypoxic cells, suggesting that the mechanism of down-regulation is along the HIF (hypoxia-inducible factor) pathway. This atypical localization of the 150 kDa protein suggests that it might play a role in nuclear calcium signalling in health and disease.

Calcium Channels, L-Type↗
PubMed2004

Unravelling calcium-release channel gating: clues from a 'hot' disease.

Ryanodine receptors (RyRs) are a family of intracellular channels that mediate Ca2+ release from the endoplasmic and sarcoplasmic reticulum. More than 50 distinct point mutations in one member of this family, RyR1, cause malignant hyperthermia, a potentially lethal pharmacogenetic disorder of skeletal muscle. These mutations are not randomly distributed throughout the primary structure of RyR1, but are grouped in three discrete clusters. In this issue of the Biochemical Journal, Kobayashi et al. present evidence that interdomain interactions between two of these mutation-enriched regions play a key role in the gating mechanism of RyR1.

Calcium↗
PubMed2001

Analysis of type 1 ryanodine receptor-12 kDa FK506-binding protein interaction.

Although dissociation of the 12 kDa FK506 binding protein (FKBP12)-type 1 ryanodine receptor (RyR1) complex by macrolide immunosuppressants is well documented, effects of many solutes and drugs have not been quantitated. In the current study, the influence of these on binding between solubilised RyR1 and an FKBP12-glutathione-S-transferase fusion protein was analysed using a novel assay. Association between these two proteins is stable, and is not greatly altered by changes in temperature, pH, cations, and endogenous solutes over physiological ranges. Ascomycin, an FK506 analogue, was identified for the first time as a drug which can disrupt the FKBP12-RyR1 complex.

Animals↗
PubMed2001

Rapid detection of the R408W and I65T mutations in phenylketonuria by glycosylase mediated polymorphism detection.

Mutation detection methods based upon chemical or enzymatic cleavage of DNA offer excellent detection efficiencies coupled with high throughput and low unit cost. We describe the application of the novel technique of Glycosylase Mediated Polymorphism Detection (GMPD) to the detection of two of the most common mutations of the PAH gene in the Irish population that cause phenylketonuria (PKU), R408W and I65T, which occur at relative frequencies of 41.0% and 10.4% respectively. GMPD assays for R408W and I65T were developed permitting fluorescent detection of cleavage products on the ALFexpresstrade mark automated DNA sequencer. The method was validated by screening a panel of PKU patients whose mutant genotypes had previously been characterised by standard methods. It also proved possible to perform multiplex detection of the two mutations by co-electrophoresis of GMPD products. GMPD is a rapid and robust method for the detection of the R408W and I65T mutations, whose key advantage lies in its use of a pair of enzymes with high cleavage efficiency to detect a number of mutations as compared to the use of individual digestions with a range of specific restriction endonuclease enzymes. Hum Mutat 17:432, 2001.

Alleles↗
PubMed2000

A novel ryanodine receptor mutation and genotype-phenotype correlation in a large malignant hyperthermia New Zealand Maori pedigree.

Malignant hyperthermia (MH) is a pharmacogenetic disorder that predisposes to a sometimes fatal hypermetabolic reaction to halogenated anaesthetics. MH is considered to originate from abnormal regulation of skeletal muscle Ca(2+) release. Current diagnosis of MH susceptibility (MHS) relies on in vitro contracture testing (IVCT) of skeletal muscle. The ryanodine receptor (RYR1) encoding the major Ca(2+) release channel in the skeletal muscle sarcoplasmic reticulum has been shown to be mutated in a number of MH pedigrees. The large Maori pedigree reported here is the largest MHS pedigree investigated to date and comprises five probands who experienced clinical episodes of MH and 130 members diagnosed by the IVCT. Sequencing of the 15 117 bp RYR1 cDNA in a MHS individual from this pedigree identified a novel C14477T transition that results in a Thr4826 to Ile substitution in the C-terminal region/transmembrane loop of the skeletal muscle ryanodine receptor. This is the first mutation in the RyR1 C-terminal region associated solely with MHS. Although linkage analysis showed strong linkage (max LOD, 11.103 at theta = 0.133) between the mutation and MHS in the pedigree using the standardized European IVCT phenotyping protocol, 22 MHS recombinants were observed. The relationship between the IVCT response and genotype was explored and showed that as IVCT diagnostic cut-off points were made increasingly stringent, the number of MHS discordants decreased with complete concordance between the presence or absence of the C14477T mutation and MHS and MH normal phenotypes, respectively, using a cut-off of 1.2 g tension at 2.0 mM caffeine and 1.8 g tension at 2.0% halothane. Many MHS pedigrees investigated have been excluded from linkage to the RYR1 gene on the basis of a small number of recombinants; however, the linkage analysis reported here suggests that other recombinant families excluded from linkage to the RYR1 gene may actually demonstrate linkage as the number of members tested within the pedigrees increases. The high number of discordants observed using the standardized diagnostic cut-off points is likely to reflect the presence of a second MHS susceptibility locus in the pedigree.

Amino Acid Sequence↗
PubMed2000

Ryanodine receptor mutations in malignant hyperthermia and central core disease.

Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle that manifests in response to anesthetic triggering agents. Central core disease (CCD) is a myopathy closely associated with MH. Both MH and CCD are primarily disorders of calcium regulation in skeletal muscle. The ryanodine receptor (RYR1) gene encodes the key channel which mediates calcium release in skeletal muscle during excitation-contraction coupling, and mutations in this gene are considered to account for susceptibility to MH (MHS) in more than 50% of cases and in the majority of CCD cases. To date, 22 missense mutations in the 15,117 bp coding region of the RYR1 cDNA have been found to segregate with the MHS trait, while a much smaller number of these mutations is associated with CCD. The majority of RYR1 mutations appear to be clustered in the N-terminal amino acid residues 35-614 (MH/CCD region 1) and the centrally located residues 2163-2458 (MH/CCD region 2). The only mutation identified outside of these regions to date is a single mutation associated with a severe form of CCD in the highly conserved C-terminus of the gene. All of the RYR1 mutations result in amino acid substitutions in the myoplasmic portion of the protein, with the exception of the mutation in the C-terminus, which resides in the lumenal/transmembrane region. Functional analysis shows that MHS and CCD mutations produce RYR1 abnormalities that alter the channel kinetics for calcium inactivation and make the channel hyper- and hyposensitive to activating and inactivating ligands, respectively. The likely deciding factors in determining whether a particular RYR1 mutation results in MHS alone or MHS and CCD are: sensitivity of the RYR1 mutant proteins to agonists; the level of abnormal channel-gating caused by the mutation; the consequential decrease in the size of the releasable calcium store and increase in resting concentration of calcium; and the level of compensation achieved by the muscle with respect to maintaining calcium homeostasis. From a diagnostic point of view, the ultimate goal of development of a simple non-invasive test for routine diagnosis of MHS remains elusive. Attainment of this goal will require further detailed molecular genetic investigations aimed at solving heterogeneity and discordance issues in MHS; new initiatives aimed at identifying modulating factors that influence the penetrance of clinical MH in MHS individuals; and detailed studies aimed at describing the full epidemiological picture of in vitro responses of muscle to agents used in diagnosis of MH susceptibility.

Amino Acid Substitution↗
PubMed1999

The lysine-specific proteinase from Armillaria mellea is a member of a novel class of metalloendopeptidases located in Basidiomycetes.

The fruiting body of the basidiomycete fungus Armillaria mellea produces a lysine-specific proteinase which exhibits both potent fibrinolytic activity and a remarkable resistance to denaturing agents. An improved purification protocol has been developed for this enzyme and the sequence of the 26 N-terminal amino acid residues of the pure protein has been determined by gas-phase sequencing. Searches of the SwissProt database showed that the N-terminal sequence of A. mellea proteinase is highly similar to those of lysine-specific metalloendopeptidases from the basidiomycetes Grifola frondosa and Pleurotus ostreatus. These results support the view that the A. mellea proteinase is a member of a novel class of lysine-specific metalloendopeptidases which may be exclusive to basidiomycete fungi.

Amino Acid Sequence↗
PubMed1999

Purification, characterization and cDNA cloning of an endo-exonuclease from the basidiomycete fungus Armillaria mellea.

We have purified an endo-exonuclease from the fruiting body of the basidiomycete fungus Armillaria mellea by using an ethanol fractionation step, followed by two rounds of column chromatography. The enzyme had an apparent molecular mass of 17500 Da and was shown to exist as a monomer by gel-filtration analysis. The nuclease was active on both double-stranded and single-stranded DNA but not on RNA. It was optimally active at pH8.5 and also exhibited a significant degree of thermostability. Three bivalent metal ions, Mg2+, Co2+ and Mn2+, acted as cofactors in the catalysis. It was also inhibited by high salt concentrations: activity was completely abolished at 150 mM NaCl. The nuclease possessed both endonuclease activity on supercoiled DNA and a 3'-5' (but not a 5'-3') exonuclease activity. It generated 5'-phosphomonoesters on its products that, after a prolonged incubation, were hydrolysed to a mixture of free mononucleotides and small oligonucleotides ranging in size from two to eight bases. Elucidation of its N-terminal amino acid sequence permitted the cDNA cloning of the A. mellea nuclease via a PCR-based approach. Peptide mapping of the purified enzyme generated patterns consistent with the amino acid sequence coded for by the cloned cDNA. A BLAST search of the SwissProt database revealed that A. mellea nuclease shared significant amino acid similarity with two nucleases from Bacillus subtilis, suggesting that the three might constitute a distinct class of nucleolytic enzymes.

Amino Acid Sequence↗
PubMed1999

A mutation in the transmembrane/luminal domain of the ryanodine receptor is associated with abnormal Ca2+ release channel function and severe central core disease.

Central core disease is a rare, nonprogressive myopathy that is characterized by hypotonia and proximal muscle weakness. In a large Mexican kindred with an unusually severe and highly penetrant form of the disorder, DNA sequencing identified an I4898T mutation in the C-terminal transmembrane/luminal region of the RyR1 protein that constitutes the skeletal muscle ryanodine receptor. All previously reported RYR1 mutations are located either in the cytoplasmic N terminus or in a central cytoplasmic region of the 5,038-aa protein. The I4898T mutation was introduced into a rabbit RYR1 cDNA and expressed in HEK-293 cells. The response of the mutant RyR1 Ca2+ channel to the agonists halothane and caffeine in a Ca2+ photometry assay was completely abolished. Coexpression of normal and mutant RYR1 cDNAs in a 1:1 ratio, however, produced RyR1 channels with normal halothane and caffeine sensitivities, but maximal levels of Ca2+ release were reduced by 67%. [3H]Ryanodine binding indicated that the heterozygous channel is activated by Ca2+ concentrations 4-fold lower than normal. Single-cell analysis of cotransfected cells showed a significantly increased resting cytoplasmic Ca2+ level and a significantly reduced luminal Ca2+ level. These data are indicative of a leaky channel, possibly caused by a reduction in the Ca2+ concentration required for channel activation. Comparison with two other coexpressed mutant/normal channels suggests that the I4898T mutation produces one of the most abnormal RyR1 channels yet investigated, and this level of abnormality is reflected in the severe and penetrant phenotype of affected central core disease individuals.

Amino Acid Sequence↗
PubMed1999

Measurement of resting cytosolic Ca2+ concentrations and Ca2+ store size in HEK-293 cells transfected with malignant hyperthermia or central core disease mutant Ca2+ release channels.

Malignant hyperthermia (MH) and central core disease (CCD) mutations were introduced into full-length rabbit Ca2+ release channel (RYR1) cDNA, which was then expressed transiently in HEK-293 cells. Resting Ca2+ concentrations were higher in HEK-293 cells expressing homotetrameric CCD mutant RyR1 than in cells expressing homotetrameric MH mutant RyR1. Cells expressing homotetrameric CCD or MH mutant RyR1 exhibited lower maximal peak amplitudes of caffeine-induced Ca2+ release than cells expressing wild type RyR1, suggesting that MH and CCD mutants might be "leaky." In cells expressing homotetrameric wild type or mutant RyR1, the amplitude of 10 mM caffeine-induced Ca2+ release was correlated significantly with the amplitude of carbachol- or thapsigargin-induced Ca2+ release, indicating that maximal drug-induced Ca2+ release depends on the size of the endoplasmic reticulum Ca2+ store. The content of endogenous sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2b (SERCA2b), measured by enzyme-linked immunosorbent assay, 45Ca2+ uptake, and confocal microscopy, was increased in HEK-293 cells expressing wild type or mutant RyR1, supporting the view that endoplasmic reticulum Ca2+ storage capacity is increased as a compensatory response to an enhanced Ca2+ leak. When heterotetrameric (1:1) combinations of MH/CCD mutant and wild type RyR1 were expressed together with SERCA1 to enhance Ca2+ reuptake, the amplitude of Ca2+ release in response to low concentrations of caffeine and halothane was higher than that observed in cells expressing wild type RyR1 and SERCA1. In Ca2+-free medium, MH/CCD mutants were more sensitive to caffeine than wild type RyR1, indicating that caffeine hypersensitivity observed with a variety of MH/CCD mutant RyR1 proteins is not dependent on extracellular Ca2+ concentration.

Animals↗
PubMed1999

IP3-induced Ca2+ release in A7r5 vascular smooth-muscle cells represents a partial emptying of the stores and not an all-or-none Ca2+ release of separate quanta.

There is still no agreement on the mechanism of the intracellular action of low concentrations of inositol 1,4,5-trisphosphate (IP3). Intracellular Ca2+ stores may transiently release some Ca2+ before they become insensitive to IP3. Alternatively, stores with a low IP3 threshold may lose all their Ca2+ and the others none. We now report that the IP3 threshold was not correlated with the extent of Ca2+ release in permeabilized A7r5 smooth-muscle cells. In contrast, the maximum rate of release, which was changed either by varying the level of IP3 receptor (IP3R) activation, or by changing the concentration of IP3R at a constant level of IP3R activation, was directly related to the extent of Ca2+ release. We conclude that IP3-induced Ca2+ release reflects partial emptying of the stores and not all-or-none Ca2+ release of separate quanta.

Adenosine Triphosphate↗
PubMed1999

Glycosylase mediated polymorphism detection (GMPD)--a novel process for genetic analysis.

A process for mutation and polymorphism detection is described here that offers significant advances over current mutation detection systems and that has the potential to significantly enhance molecular genetic analysis of human disease. This novel process is referred to as glycosylase mediated polymorphism detection (GMPD) and exploits the use of highly specific DNA glycosylase enzymes to excise substrate bases incorporated into amplified DNA. Action of the glycosylase leaves the DNA with one or more specific abasic sites which can be cleaved by enzymatic or chemical means. The GMPD process permits detection of polymorphisms and mutations using fragment size analysis or solid phase formats. GMPD is particularly suitable for genotyping of single nucleotide polymorphism (SNP) based markers and also permits efficient scanning of genes for unknown polymorphisms and mutations.

DNA Mutational Analysis↗
PubMed1998

A novel process for mutation detection using uracil DNA-glycosylase.

A novel process is presented for the detection of known mutations and polymorphisms in DNA. This process, termed glycosylase mediated polymorphism detection (GMPD) involves amplification of the target DNA using three normal dNTPs and a fourth modified dNTP, whose base is a substrate for a specific DNA-glycosylase once incorporated into the DNA. The work described here utilises uracil DNA-glycosylase as the specific glycosylase and dUTP as the modified dNTP. Primers are designed so that during extension, the position of the first uracil incorporated into the extended primers differs depending on whether a mutation is present or absent. Subsequent glycosylase excision of the uracil residues followed by cleavage of the apyrimidinic sites allows detection of the mutation in the amplified fragment as a fragment length polymorphism. Variation in the sizes of the fragment length polymorphisms generated, can be readily achieved through the use of inosine bases in place of adenine bases in the upper and/or lower primers. The GMPD process is also adaptable to solid phase analysis. The use of the process for detection of mutations in the RYR1 and CFTR genes is demonstrated. Overall, the simplicity, specificity, versatility and flexibility of the GMPD process make it an attractive candidate for both small and large scale application in mutation detection and genome analysis.

Base Sequence↗
PubMed1998

Sequence analysis of DNA randomly amplified from the Saccharomyces cerevisiae genome.

Despite its widespread use, the molecular basis of random amplification is poorly understood. Here the basis of random amplification has been investigated by cloning and sequencing the products of a random amplification of polymorphic DNA (RAPD) amplification from Saccharomyces cerevisiae DNA. The genomic origin of the amplified products was determined by sequence comparison with the S. cerevisiae Genome Database (SGD). This allowed analysis of the degree of identity between the random primer and the primer binding sites on the genome. There was no relationship between RAPD size, GC content and relative abundance. The degree of matching between the primer and the primer binding sites increased towards the 3; end of the primer and decreased towards the 5; end. The maximum number of mismatches observed between primer and primer binding sites was never more than one between positions 1-7 of the primer. Nucleotide compositional biases were also observed upstream and downstream of the primer binding site with a marked preference for AT richness upstream of the primer binding sites and for a GC preference directly following the 3; end of the primer. These findings have important ramifications for primer design for multiplex, low stringency and degenerate polymerase chain reaction (PCR).

Base Sequence↗
PubMed1998

Identification of novel mutations in the ryanodine-receptor gene (RYR1) in malignant hyperthermia: genotype-phenotype correlation.

Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle that is triggered in genetically predisposed individuals by common anesthetics and muscle relaxants. The ryanodine receptor (RYR1) is mutated in a number of MH pedigrees, some members of which also have central core disease (CCD), an inherited myopathy closely associated with MH. Mutation screening of 6 kb of the RYR1 gene has identified four adjacent novel mutations, C6487T, G6488A, G6502A, and C6617T, which result in the amino acid alterations Arg2163Cys, Arg2163His, Val2168Met, and Thr2206Met, respectively. Collectively, these mutations account for 11% of MH cases and identify the gene segment 6400-6700 as a mutation hot spot. Correlation analysis of the in vitro contracture-test data available for pedigrees bearing these and other RYR1 mutations showed an exceptionally good correlation between caffeine threshold and tension values, whereas no correlation was observed between halothane threshold and tension values. This finding has important ramifications for assignment of the MH-susceptible phenotype, in genotyping studies, and indicates that assessment of recombinant individuals on the basis of caffeine response is justified, whereas assessment on the basis of halothane response may be problematic. Interestingly, the data suggest a link between the caffeine threshold and tension values and the MH/CCD phenotype.

Female↗