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Biomedical subjects

S Silberstein

Publications and source records attributed to S Silberstein.

At least 19 recordsLinked to original sources
PubMed2004

Practice parameter: pharmacological treatment of migraine headache in children and adolescents [RETIRED]: report of the American Academy of Neurology Quality Standards Subcommittee and the Practice Committee of the Child Neurology Society.

OBJECTIVE: To review evidence on the pharmacologic treatment of the child with migraine headache. METHODS: The authors reviewed, abstracted, and classified relevant literature. Recommendations were based on a four-tiered scheme of evidence classification. Treatment options were separated into medications for acute headache and preventive medications. RESULTS: The authors identified and reviewed 166 articles. For acute treatment, five agents were reviewed. Sumatriptan nasal spray and ibuprofen are effective and are well tolerated vs placebo. Acetaminophen is probably effective and is well tolerated vs placebo. Rizatriptan and zolmitriptan were safe and well tolerated but were not superior to placebo. For preventive therapy, 12 agents were evaluated. Flunarizine is probably effective. The data concerning cyproheptadine, amitriptyline, divalproex sodium, topiramate, and levetiracetam were insufficient. Conflicting data were found concerning propranolol and trazodone. Pizotifen, nimodipine, and clonidine did not show efficacy. CONCLUSIONS: For children (>age 6 years), ibuprofen is effective and acetaminophen is probably effective and either can be considered for the acute treatment of migraine. For adolescents (>12 years of age), sumatriptan nasal spray is effective and should be considered for the acute treatment of migraine. For preventive therapy, flunarizine is probably effective and can be considered, but is not available in the United States. There are conflicting or insufficient data to make any other recommendations for the preventive therapy of migraine in children and adolescents. For a clinical problem so prevalent in children and adolescents, there is a disappointing lack of evidence from controlled, randomized, and masked trials.

Adolescent↗
PubMed2004

Randomized, placebo-controlled trial of rofecoxib in the acute treatment of migraine.

OBJECTIVE: To investigate the clinical profile of rofecoxib, a long-acting (approximately 17-hour half-life) selective cyclo-oxygenase-2 inhibitor, for the acute treatment of migraine. METHODS: A randomized, double-blind, placebo-controlled, parallel-group study was conducted. Patients age > or =18 treated a moderate or severe migraine headache with placebo (n = 182), rofecoxib 25 mg (n = 183), or rofecoxib 50 mg (n = 192). The primary efficacy measure was headache relief (mild or no pain) 2 hours after dose. RESULTS: The proportions of patients with migraine headache relief at 2 hours after dose were 34.3% for placebo, 54.0% for rofecoxib 25 mg (p < 0.001 vs placebo), and 56.7% for rofecoxib 50 mg (p < 0.001 vs placebo). Rofecoxib 25 and 50 mg were superior to placebo in providing pain freedom at 2 hours, 24-hour sustained headache relief, and 24-hour sustained pain freedom; in reducing photophobia, phonophobia, nausea (50 mg only), and functional disability at 2 hours after dose; and in improving some quality-of-life scores over 24 hours. More patients on rofecoxib 50 mg reported adverse events (39.6%) than patients on rofecoxib 25 mg (26.8%) or placebo (23.6%) regardless of drug relatedness; however, the incidences of drug-related adverse events were similar between treatment groups. These adverse events were generally mild or moderate in severity. The most commonly reported adverse events were dry mouth, dizziness, somnolence, nausea, dyspepsia, paresthesia, and asthenia, with similar incidences between treatment groups. CONCLUSION: Rofecoxib 25 and 50 mg were effective and generally well tolerated for the acute treatment of migraine attacks.

Acute Disease↗
PubMed2002

A randomized trial of divalproex sodium extended-release tablets in migraine prophylaxis.

OBJECTIVE: To evaluate the efficacy and safety of extended-release divalproex sodium compared with placebo in prophylactic monotherapy treatment of migraine headache. METHODS: This was a double-blind, randomized, placebo-controlled, parallel-group study. Subjects with more than two migraine headache attacks during a 4-week baseline were randomly assigned in a 1:1 ratio at each center to receive either extended-release divalproex sodium or matching placebo once daily for 12 weeks. Subjects initiated treatment on 500 mg once daily for 1 week, and the dose was then increased to 1,000 mg once daily with an option, if intolerance occurred, to permanently decrease the dose to 500 mg during the second week. Reduction from baseline in 4-week migraine headache rate was the primary efficacy variable. Migraine headaches separated by a < 24-hour headache-free interval were counted as single migraines in calculating migraine headache rates. Tolerance and safety were also evaluated. RESULTS: The mean reductions in 4-week migraine headache rate were 1.2 (from a baseline mean of 4.4) in the extended-release divalproex sodium group and 0.6 (from a baseline mean of 4.2) in the placebo group (p = 0.006); reductions with extended-release divalproex sodium were significantly greater than with placebo in all three 4-week segments of the treatment period. No significant differences were detected between treatment groups in either the overall incidence or in the incidence of any specific treatment-emergent adverse event; 8% of subjects treated with extended-release divalproex sodium and 9% of those treated with placebo discontinued for adverse events. CONCLUSION: Extended-release divalproex sodium is an efficacious, well-tolerated, safe, and easy-to-use once-a-day prophylactic antimigraine medication.

Adolescent↗
PubMed2001

Occurrence of a putative SCF ubiquitin ligase complex in Drosophila.

Many proteins are targeted to proteasome degradation by a family of E3 ubiquitin ligases, termed SCF complexes, that link substrate proteins to an E2 ubiquitin-conjugating enzyme. SCFs are composed of three core proteins-Skp1, Cdc53/Cull, Rbx1/Hrt1-and a substrate specific F-box protein. We have identified in Drosophila melanogaster the closest homologues to the human components of the SCF(betaTrCP) complex and the E2 ubiquitin-conjugating enzyme UbcH5. We show that putative Drosophila SCF core subunits dSkpA and dRbx1 both interact directly with dCu11 and the F-box protein Slmb. We also describe the direct interaction of the UbcH5 related protein UbcD1 with dCul1 and Slmb. In addition, a functional complementation test performed on a Saccharomyces cerevisiae Hrt1p-deficient mutant showed that Drosophila Rbx1 is able to restore the yeast cells viability. Our results suggest that dRbx1, dSkpA, dCullin1, and Slimb proteins are components of a Drosophila SCF complex that functions in combination with the ubiquitin conjugating enzyme UbcD1.

Amino Acid Sequence↗
PubMed2001

How to pick optimal acute treatment for migraine headache.

Drug selection for the acute treatment of migraine is based on comorbid disorders, coexistent diseases, and the patient's pain profile and specific needs and expectations. Patients should be instructed to tailor their treatment strategy to meet their specific needs by varying their medications according to pain intensity. This will aid in successful headache management, by increasing compliance and decreasing disability and cost.

Analgesics↗
PubMed2001

Preference comparison of rizatriptan ODT 10-mg and sumatriptan 50-mg tablet in migraine.

OBJECTIVE: To compare the proportion of patients who prefer rizatriptan orally disintegrating tablet (ODT) 10-mg to sumatriptan 50-mg tablet. BACKGROUND: Migraineurs express treatment preference based on a variety of attributes including the speed of pain relief and medication formulation. Rizatriptan ODT is an orally disintegrating formulation of rizatriptan, a selective 5-HT1B/1D receptor agonist. This study was conducted to determine patient preference between rizatriptan ODT 10-mg and sumatriptan 50-mg tablet for the acute treatment of migraine. METHODS: This was a multicenter, randomized, open-label, two-period crossover study conducted in the United States with 524 enrolled patients. Patients treated a single moderate or severe headache in each treatment period. Patients treated one migraine with either rizatriptan ODT 10-mg or sumatriptan 50-mg tablet, then treated a second migraine with the alternate therapy. Patients completed diary assessments at baseline, and 30, 45, 60, 90, and 120 minutes postdose and rated headache severity on a 4-point scale (0 = none, 1 = mild, 2 = moderate, and 3 = severe). At the final study visit following treatment of their second migraine, patients expressed preference for one of the two study medications by completing an interviewer-administered Global Preference Question and then responded to a self-administered series of questions to capture their most important reason for preferring one study medication over the other. Safety measurements were recorded through standard adverse experience reporting. RESULTS: Three hundred eighty-six patients treated two migraine attacks. For those patients who expressed a preference for either rizatriptan ODT or sumatriptan (n = 374), the percentage of patients who preferred rizatriptan ODT 10-mg (57%, n = 213) was significantly greater than those who preferred sumatriptan 50-mg tablet (43%, n = 161) (P<.01). For those patients who treated two migraine attacks and had drug severity measures for both attacks (n = 384), a significantly greater percentage of patients reported pain relief after taking rizatriptan ODT than sumatriptan at the 45- and 60-minute time points (38% versus 29% and 58% versus 49%, respectively) (P<.01). In addition, a significantly greater percentage of patients taking rizatriptan ODT reported a pain-free status at the 60- and 120-minute time points (23% versus 17% [P<.05] and 60% versus 52% [P<.01], respectively). Both rizatriptan ODT and sumatriptan were well tolerated. CONCLUSIONS: A significantly greater proportion of patients preferred rizatriptan ODT 10-mg to sumatriptan 50-mg tablet for the acute treatment of migraine. Efficacy and safety data are consistent with the preference findings.

Adult↗
PubMed2001

Naratriptan as short-term prophylaxis of menstrually associated migraine: a randomized, double-blind, placebo-controlled study.

OBJECTIVE: To determine the efficacy of naratriptan 1-mg and 2.5-mg tablets twice daily compared with placebo as short-term prophylaxis of menstrually associated migraine. BACKGROUND: Approximately 60% of women with migraine report headaches associated with their menstrual cycles. Results from an open-label study suggest that short-term administration of sumatriptan is useful in the prophylaxis of menstrually associated migraine. METHODS: A randomized, double-blind, three-arm, parallel-group, placebo-controlled study was conducted in women aged 18 years or older with a history of migraine with or without aura, as defined by the International Headache Society, of at least 6 months. Two dose strengths of naratriptan (1 mg, 2.5 mg) or identical-appearing placebo tablets (1:1:1) were administered twice daily for 5 days starting 2 days prior to the expected onset of menses across four perimenstrual periods. End points included the number of menstrually associated migraines, total migraine days, peak headache severity, lost work/activity time, migraine-related quality of life, and incidence of adverse events. RESULTS: Overall, the intent-to-treat population comprised 206 women (naratriptan 1 mg, n = 70; naratriptan 2.5 mg, n = 70, and placebo, n = 66); 171 women treated four perimenstrual periods. Significantly more perimenstrual periods per subject treated with naratriptan, 1 mg, were headache-free compared with placebo (50% versus 25%, P =.003). Naratriptan, 1 mg, significantly reduced the number of menstrually associated migraines (2.0 versus 4.0, P <.05) and menstrually associated migraine days (4.2 versus 7.0, P <.01) compared with placebo. More patients treated with naratriptan, 1 mg, were headache-free across all treated perimenstrual periods compared with placebo (23% versus 8%). No difference in headache severity was observed in breakthrough headaches. The incidence and severity of adverse events was similar across treatment groups. Naratriptan, 2.5 mg, was not statistically superior to placebo for any measure. CONCLUSIONS: Naratriptan, 1 mg, with tolerability similar to placebo, is an effective, short-term, prophylactic treatment for menstrually associated migraine.

Adult↗
PubMed2000

Pharmacodynamics of oestrogens and progestogens.

The ovaries cyclically secrete estradiol and progesterone. Cyclic ovarian estradiol secretion is associated with a bone-saving and vascular protection effect. Endogenous progesterone does not modify the vasodilator effect of oestrogens. At physiological concentrations, the natural sex steroids have low antigonadotropic effects. More potent synthetic derivatives with more antigonadotropic effects were synthesized in the 1950s. After the menopause, there is no longer any need to use hormonal steroids as antigonadotropics. In addition, vascular contraindications are more common in an older population. Contraceptive steroids (particularly ethinyl estradiol) are therefore rarely used. The oestrogen that is most widely prescribed for post-menopausal replacement is a complex formulation of conjugated oestrogens of equine origin that is administered orally in a single daily dose. Improvements in hormone replacement therapy may result from the use of parenteral estradiol (providing sufficient doses are reached) and of a progestogen chemically more similar to progesterone.

Contraceptives, Oral↗
PubMed2000

Botulinum toxin type A as a migraine preventive treatment. For the BOTOX Migraine Clinical Research Group.

OBJECTIVE: To assess the safety and efficacy of botulinum toxin type A (BOTOX; Allergan, Inc) in the prevention of migraine. BACKGROUND: Current migraine preventive therapies are often unsatisfactory because of their limited efficacy, adverse effects, and drug interactions. Botulinum toxin type A injections often reduce the pain associated with conditions such as cervical dystonia, achalasia, rectal fissures, and myofascial pain syndrome. An open-label, noncontrolled study of botulinum toxin type A suggested benefits for patients with migraine. DESIGN AND METHODS: This was a double-blind, vehicle-controlled study of 123 subjects with a history of two to eight moderate-to-severe migraine attacks per month, with or without aura. Participants were randomized to receive single administrations of vehicle or botulinum toxin type A, 25 U or 75 U, injected into multiple sites of pericranial muscles at the same visit. During a 1-month baseline period and for 3 months following injection, subjects kept daily diaries in which they recorded migraine frequency, migraine severity, and the occurrence of migraine-associated symptoms. RESULTS: Compared with vehicle treatment, subjects in the 25-U botulinum toxin type A treatment group showed significantly fewer migraine attacks per month, a reduced maximum severity of migraines, a reduced number of days using acute migraine medications, and reduced incidence of migraine-associated vomiting. Both the 25-U and 75-U botulinum toxin type A groups were significantly better than the vehicle group on subject global assessment. Botulinum toxin A treatment was well tolerated, with only the 75-U treatment group exhibiting a significantly higher rate of treatment-related adverse events than vehicle. CONCLUSIONS: Pericranial injection of botulinum toxin type A, 25 U, was found to be a safe treatment that significantly reduced migraine frequency, migraine severity, acute medication usage, and associated vomiting.

Adolescent↗
PubMed1999

Sex hormones and headache 1999 (menstrual migraine).

The normal female life cycle is associated with a number of hormonal milestones: menarche, pregnancy, contraceptive use, menopause, and the use of replacement sex hormones. All these events and interventions alter the levels and cycling of sex hormones and may cause a change in the prevalence or intensity of headache. The menstrual cycle is the result of a carefully orchestrated sequence of interactions among the hypothalamus, pituitary, ovary, and endometrium, with the sex hormones acting as modulators and effectors at each level. Estrogen and progestins have potent effects on central serotonergic and opioid neurons, modulating both neuronal activity and receptor density. The primary trigger of menstrual migraine appears to be the withdrawal of estrogen rather than the maintenance of sustained high or low estrogen levels. However, changes in the sustained estrogen levels with pregnancy (increased) and menopause (decreased) appear to affect headaches. Headaches that occur with premenstrual syndrome appear to be centrally generated, involving the inherent rhythm of CNS neurons, including perhaps the serotonergic pain-modulating systems.

Female↗
PubMed1998

A role for the DnaJ homologue Scj1p in protein folding in the yeast endoplasmic reticulum.

Members of the eukaryotic heat shock protein 70 family (Hsp70s) are regulated by protein cofactors that contain domains homologous to bacterial DnaJ. Of the three DnaJ homologues in the yeast rough endoplasmic reticulum (RER; Scj1p, Sec63p, and Jem1p), Scj1p is most closely related to DnaJ, hence it is a probable cofactor for Kar2p, the major Hsp70 in the yeast RER. However, the physiological role of Scj1p has remained obscure due to the lack of an obvious defect in Kar2p-mediated pathways in scj1 null mutants. Here, we show that the Deltascj1 mutant is hypersensitive to tunicamycin or mutations that reduce N-linked glycosylation of proteins. Although maturation of glycosylated carboxypeptidase Y occurs with wild-type kinetics in Deltascj1 cells, the transport rate for an unglycosylated mutant carboxypeptidase Y (CPY) is markedly reduced. Loss of Scj1p induces the unfolded protein response pathway, and results in a cell wall defect when combined with an oligosaccharyltransferase mutation. The combined loss of both Scj1p and Jem1p exaggerates the sensitivity to hypoglycosylation stress, leads to further induction of the unfolded protein response pathway, and drastically delays maturation of an unglycosylated reporter protein in the RER. We propose that the major role for Scj1p is to cooperate with Kar2p to mediate maturation of proteins in the RER lumen.

Alleles↗
PubMed1998

Efficacy and safety of acetaminophen, aspirin, and caffeine in alleviating migraine headache pain: three double-blind, randomized, placebo-controlled trials.

OBJECTIVE: To assess the effectiveness of the nonprescription combination of acetaminophen, aspirin, and caffeine in alleviating migraine headache pain. DESIGN: Three double-blind, randomized, parallel-group, single-dose, placebo-controlled studies. SETTING: Private practice, referral centers, and general community. PATIENTS: Migraineurs with moderate or severe headache pain who met International Headache Society diagnostic criteria for migraine with aura or without aura. The most severely disabled segment of migraineurs, including those whose attacks usually required bed rest, or who vomited 20% or more of the time, were excluded. Of the 1357 enrolled patients, 1250 took study medication and 1220 were included in the efficacy-evaluable data set. INTERVENTION: Two tablets of the nonprescription combination of acetaminophen, aspirin, and caffeine or placebo taken orally as a single-dose treatment of 1 eligible acute migraine attack. MAIN OUTCOME MEASURES: Pain intensity difference from baseline; percentage of patients with pain reduced to mild or none. RESULTS: Significantly greater reductions in migraine headache pain intensity 1 to 6 hours after dose were seen in patients taking the acetaminophen, aspirin, and caffeine combination than in those taking placebo in each of the 3 studies. Pain intensity was reduced to mild or none 2 hours after dose in 59.3% of the 602 drug-treated patients compared with 32.8% of the 618 placebo-treated patients (P< .001; 95% confidence interval [CI], 55%-63% for drug, 29%-37% for placebo); at 6 hours after dose, 79% vs 52%, respectively, had pain reduced to mild or none (P<.001; 95% CI, 75%-82% vs 48%-56%). In addition, by 6 hours after dose, 50.8% of the drug-treated patients were pain free compared with 23.5% of the placebo-treated patients (P<.001; 95% CI, 47%-55% for drug, 20%-27% for placebo). Other migraine headache characteristics, such as nausea, photophobia, phonophobia, and functional disability, were significantly improved 2 to 6 hours after treatment with the acetaminophen, aspirin, and caffeine combination compared with placebo (P< or =.01). CONCLUSIONS: The nonprescription combination of acetaminophen, aspirin, and caffeine was highly effective for the treatment of migraine headache pain as well as for alleviating the nausea, photophobia, phonophobia, and functional disability associated with migraine attacks. This drug combination also has an excellent safety profile and is well tolerated.

Acetaminophen↗
PubMed1998

A placebo-controlled crossover study of rizatriptan in the treatment of multiple migraine attacks. Rizatriptan Multiple Attack Study Group.

OBJECTIVE: To examine the safety and efficacy of rizatriptan 10 mg PO in the treatment of multiple migraine attacks. BACKGROUND: Rizatriptan is a potent and rapidly absorbed 5-HT1B/1D receptor agonist. Efficacy and general safety have been examined in controlled trials treating single migraine attacks. In the current placebo-controlled study, we report constancy of safety and efficacy of rizatriptan for patients treating four discrete migraine attacks. METHODS: Patients with moderate or severe migraine (n = 473) were randomized to one of five sequence groups, in which each patient was to treat four migraine attacks. Patients in four groups received rizatriptan 10 mg for three of four attacks and placebo for the remaining attack. Patients in the fifth group received rizatriptan 10 mg for four attacks. Headache severity, functional disability, and migraine symptoms were measured immediately before dosing and at 0.5, 1, 1.5, 2, 3, and 4 hours postdose. RESULTS: After the first attack, response rates were 77% for rizatriptan and 37% for placebo (p < 0.001). Similar efficacy of rizatriptan, ranging from a 75 to 80% response, was observed in each of the subsequent attacks with no evidence of tolerance to therapeutic effects. Most patients (93%) responded to rizatriptan 10 mg during the first or second attack. Adverse experiences were generally mild and transient, the most common being dizziness and somnolence. Incidence of adverse experiences per attack decreased after the first attack. CONCLUSIONS: Rizatriptan 10 mg PO is efficacious and generally well tolerated in acute migraine. Its efficacy is maintained throughout the treatment of multiple, discrete migraine attacks.

Administration, Oral↗
PubMed1996

t(15;21)(q15;q22.1) pat resulting in partial trisomy and partial monosomy of chromosomes 15 and 21 in two offspring.

Two sibs, carriers of unbalanced products of the translocation t(15;21)(q15;q22.1) pat, are described. The sister had Prader-Willi syndrome due to deletion 15 (pter > q15) and partial trisomy 21 (pter > q22.1); her brother had partial trisomy 15 (pter > q15) and partial monosomy 21 (pter > q22.1). The translocation breakpoint on chromosome 21 was located proximal to the SOD1 gene, within a region of 4.0 cM (2.3 Mb) between the loci D21S217 and D21S213. The correlations between the clinical presentation and the molecular findings of the two sibs are discussed in relation to other patients with partial trisomy and monosomy 21.

Adolescent↗
PubMed1996

Biochemistry, molecular biology, and genetics of the oligosaccharyltransferase.

Asparagine-linked glycosylation is a highly conserved protein modification reaction that occurs in all eukaryotes. The initial stage in the biosynthesis of N-linked glycoproteins, catalyzed by the enzyme oligosaccharyltransferase (OST), involves the transfer of a preassembled high-mannose oligosaccharide from a dolichol-linked oligosaccharide donor onto asparagine acceptor sites in nascent proteins in the lumen of the rough endoplasmic reticulum. Biochemical, molecular biological, and genetic studies conducted during the past 5 years have resulted in an explosive growth in our knowledge concerning the OST. Although the basic biochemical properties of the enzyme were determined more than a decade ago using intact microsomal membranes, recent studies provide novel insight into the catalytic mechanism of the enzyme. The OST was recently purified as a large heteroligomeric membrane protein complex; the sequences of many of the subunits have been determined from both fungal and vertebrate sources. Consistent with the evolutionary conservation of N-linked glycosylation, protein sequence comparisons reveal significant homologies between vertebrate, invertebrate, plant, and fungal OST subunits. Yeast molecular genetic methods have been instrumental in the functional characterization of the OST subunits, and have proven to be powerful tools for the identification of novel gene products that influence oligosaccharide transfer in vivo.

Animals↗
PubMed1995

The alpha subunit of the Saccharomyces cerevisiae oligosaccharyltransferase complex is essential for vegetative growth of yeast and is homologous to mammalian ribophorin I.

Oligosaccharyltransferase mediates the transfer of a preassembled high mannose oligosaccharide from a lipid-linked oligosaccharide donor to consensus glycosylation acceptor sites in newly synthesized proteins in the lumen of the rough endoplasmic reticulum. The Saccharomyces cerevisiae oligosaccharyltransferase is an oligomeric complex composed of six nonidentical subunits (alpha-zeta), two of which are glycoproteins (alpha and beta). The beta and delta subunits of the oligosaccharyltransferase are encoded by the WBP1 and SWP1 genes. Here we describe the functional characterization of the OST1 gene that encodes the alpha subunit of the oligosaccharyltransferase. Protein sequence analysis revealed a significant sequence identity between the Saccharomyces cerevisiae Ost1 protein and ribophorin I, a previously identified subunit of the mammalian oligosaccharyltransferase. A disruption of the OST1 locus was not tolerated in haploid yeast showing that expression of the Ost1 protein is essential for vegetative growth of yeast. An analysis of a series of conditional ost1 mutants demonstrated that defects in the Ost1 protein cause pleiotropic underglycosylation of soluble and membrane-bound glycoproteins at both the permissive and restrictive growth temperatures. Microsomal membranes isolated from ost1 mutant yeast showed marked reductions in the in vitro transfer of high mannose oligosaccharide from exogenous lipid-linked oligosaccharide to a glycosylation site acceptor tripeptide. Microsomal membranes isolated from the ost1 mutants contained elevated amounts of the Kar2 stress-response protein.

Amino Acid Sequence↗
PubMed1995

The essential OST2 gene encodes the 16-kD subunit of the yeast oligosaccharyltransferase, a highly conserved protein expressed in diverse eukaryotic organisms.

Oligosaccharyltransferase catalyzes the transfer of a preassembled high mannose oligosaccharide from a dolichol-oligosaccharide donor to consensus glycosylation acceptor sites in newly synthesized proteins in the lumen of the rough endoplasmic reticulum. The Saccharomyces cerevisiae oligosaccharyltransferase is an oligomeric complex composed of six non-identical subunits (alpha-zeta). The alpha, beta, gamma, and delta subunits of the oligosaccharyltransferase are encoded by the OST1, WBP1, OST3, and SWP1 genes, respectively. Here we describe the functional characterization of the OST2 gene that encodes the epsilon-subunit of the oligosaccharyltransferase. Genomic disruption of the OST2 locus was lethal in haploid yeast showing that expression of the Ost2 protein is essential for viability. Overexpression of the Ost2 protein suppresses the temperature-sensitive phenotype of the wbp1-2 allele and increases in vivo and in vitro oligosaccharyltransferase activity in a wbp1-2 strain. An analysis of a series of conditional ost2 mutants demonstrated that defects in the Ost2 protein cause pleiotropic underglycosylation of soluble and membrane-bound glycoproteins. Microsomal membranes isolated from ost2 mutant yeast show marked reductions in the in vitro transfer of high mannose oligosaccharide from exogenous lipid-linked oligosaccharide to a glycosylation site acceptor tripeptide. Surprisingly, the Ost2 protein was found to be 40% identical to the DAD1 protein (defender against apoptotic cell death), a highly conserved protein initially identified in vertebrate organisms. The protein sequence of ost2 mutant alleles revealed mutations at highly conserved residues in the Ost2p/DAD1 protein sequence.

Amino Acid Sequence↗