In Vitro Study of Encapsulation Therapy for Fabry Disease Using Genetically Engineered CHO Cell Line

Fabry disease is an X-linked recessive disorder caused by a deficiency of the lysosomal hydrolase α-galac-tosidase A (α-gal). The deficiency of this enzyme leads to the systemic deposition of ceramide trihexoside (CTH) in various tissues and organs. Enzyme replacement using IV doses of recombinant human α-gal produced in CHO cells or in human fibroblasts is currently being evaluated in clinical trials as a potential therapy for this disease. However, it requires lifelong therapy involving a large amount of purified α-gal. As a novel approach for treatment of Fabry disease we used polymer encapsulated Chinese hamster ovary (CHO) cells genetically modified to express α-gal. The secreted high levels of α-gal passed through the semipermeable polymeric membrane. Using coculture system with Fabry fibroblasts, the secreted enzyme was taken up in cells, resulting in reduced accumulation of CTH in Fabry fibroblasts. This in vitro study demonstrated that an encapsulated α-gal-secreting cell line can be used to treat Fabry mice by transplantation in vivo. Judging from the protection against immune rejection by a semipermeable synthetic membrane, this novel approach may be applied to treat patients with Fabry disease and other lysosomal storage diseases.

Late onset variants in Fabry disease: Results in high risk population screenings in Argentina

Background

Screening for Fabry disease (FD) in high risk populations yields a significant number of individuals with novel, ultra rare genetic variants in the GLA gene, largely without classic manifestations of FD. These variants often have significant residual α-galactosidase A activity. The establishment of the pathogenic character of previously unknown or rare variants is challenging but necessary to guide therapeutic decisions.

Objectives

To present 2 cases of non-classical presentations of FD with renal involvement as well as to discuss the importance of high risk population screenings for FD.

Results

Our patients with non-classical variants were diagnosed through FD screenings in dialysis units. However, organ damage was not limited to kidneys, since LVH, vertebrobasilar dolichoectasia and cornea verticillata were also present. Lyso-Gb3 concentrations in plasma were in the pathologic range, compatible with late onset FD. Structural studies and in silico analysis of p.(Cys174Gly) and p.(Arg363His), employing different tools, suggest that enzyme destabilization and possibly aggregation could play a role in organ damage.

Conclusions

Screening programs for FD in high risk populations are important as FD is a treatable multisystemic disease which is frequently overlooked in patients who present without classical manifestations.

Hepatocyte growth factor stimulates root growth during the development of mouse molar teeth

BACKGROUND AND OBJECTIVE

It is well known that tooth root formation is initiated by the development of Hertwig's epithelial root sheath (HERS). However, relatively little is known about the regulatory mechanisms involved in root development. As hepatocyte growth factor (HGF) is one of the mediators of epithelial-mesenchymal interactions in rodent tooth, the objective of this study was to examine the effects of HGF on the root development of mouse molars.

MATERIAL AND METHODS

The HERS of mouse molars and HERS01a, a cell line originated from HERS, were used in this study. For detection of HGF receptors in vivo and in vitro, we used immunochemical procedures. Root development was assessed by implanting molar tooth germs along with HGF-soaked beads into kidney capsules, by counting cell numbers in HERS01a cell cultures and by performing a 5'-bromo-2'-deoxyuridine (BrdU) assay in an organ-culture system.

RESULTS

HGF receptors were expressed in the enamel epithelium of molar germs as well as in HERS cells. HGF stimulated root development in the transplanted tooth germs, the proliferation of HERS01a cells in culture and HERS elongation in the organ-culture system. Examination using BrdU revealed that cell proliferation in HERS was increased by treatment with HGF, especially that in the outer layer of HERS. This effect was down-regulated when antibody against HGF receptor was present in the culture medium.

CONCLUSION

Our results raise the possibility that HGF signaling controls root formation via the development of HERS. This study is the first to show that HGF is one of the stimulators of root development.

Transcriptional regulation of phosphoenolpyruvate synthase by maltose in the hyperthermophilic archaeon, Pyrococcus furiosus

The phosphoenolpyruvate synthase (EC 2.7.9.2) from the hyperthermophilic archaeon Pyrococcus furiosus catalyzes the Pi-dependent formation of pyruvate, ATP and water from phosphoenolpyruvate and AMP [Sakuraba, H., Arch. Biochem. Biophys., 364, 125-128 (1999)]. In this study, the P. furiosus phosphoenolpyruvate synthase was purified to homogeneity and the N-terminal amino acid sequence was determined to be AYRFIKWFEELS. The sequence coincided completely with the N-terminal amino acid sequence of the translation product of the mlrA gene that was found to be upregulated at the transcriptional level by the alpha-linked glucose disaccharide maltose [Robinson, K.A. and Schreier, H.J., Gene, 151, 173-176 (1994)]. The mlrA gene was cloned and expressed in Escherichia coli. The recombinant cells produced a hyperthermostable phosphoenolpyruvate synthase. This indicates that the mlrA gene encodes the enzyme. When P. furiosus was grown on the medium supplemented with maltose, the specific activity of the enzyme markedly increased (about 10-fold) compared with that produced by the cells grown on the medium without maltose. Northern blot analysis revealed enhanced transcription of the mlrA gene in the presence of maltose. These results indicate that transcriptional regulation of phosphoenolpyruvate synthase by maltose is present in P. furiosus.

Immunoelectron-microscopic detection of globotriaosylceramide accumulated in the skin of patients with Fabry disease

BACKGROUND

Fabry disease is characterized by the systemic accumulation of glycosphingolipids, particularly in the lysosomes of vascular endothelial cells of most organs due to the deficient activity of alpha-galactosidase A. The major glycolipid accumulated in tissue is globotriaosylceramide (GL-3). To date, no direct detection of GL-3 by immunoelectron microscopy has been reported.

OBJECTIVES

To examine whether GL-3 is accumulated exclusively in lysosomes of cutaneous cells using an anti-GL-3 monoclonal antibody (mAb) and immunoelectron microscopy.

METHODS

Skin specimens from seven patients with Fabry disease were examined immunohistochemically by light and electron microscopy using an anti-GL-3 mAb.

RESULTS

By light microscopy, the cytoplasm of vascular endothelial cells, eccrine gland cells, and perineurium was stained with mouse anti-GL-3 antibody. Electron microscopically, positive signals for GL-3 were limited to dilated lysosomes in the cytoplasm of endothelial cells, pericytes, eccrine gland cells, dermal fibroblasts and perineurium.

CONCLUSIONS

Our results demonstrate that the cytoplasmic deposit in Fabry disease was GL-3 and the accumulated GL-3 was localized essentially to lysosomes.

Enzyme replacement therapy in Japanese Fabry disease patients: the results of a phase 2 bridging study

Fabry Disease (alpha-galactosidase A deficiency) is an X-linked hereditary disorder leading to the pathological accumulation of globotriaosylceramide (GL-3) in lysosomes, particularly in the vascular endothelium of the kidney, heart and brain. We report the results of an open-label phase 2 study that was undertaken to evaluate whether ethnic differences exist that would affect agalsidase beta (Fabrazyme) treatment of Fabry patients in the Japanese population, relative to safety and efficacy. The study design mirrored the design of the completed phase 3 clinical trial that led to approval of the product agalsidase beta. The 13 Japanese, male Fabry patients enrolled in the study received the enzyme replacement therapy over a period of 20 weeks as biweekly infusions. All selected efficacy end points showed improvements that were comparable with findings from the phase 3 study. These improvements included reductions of GL-3 accumulation in both kidney and skin capillary endothelial cells to (near) normal levels (92% of patients). Kidney and plasma GL-3 levels decreased by 51.9% and 100%, respectively, by ELISA. Renal function remained normal. Fabry-associated pain, and quality of life, showed improvement over baseline in multiple categories. Related adverse events were mild or moderate in intensity and mostly infusion-associated (fever and rigors). As expected, IgG antibody formation was observed in 85% of the patients, but had no effect on treatment response. These results suggest that treatment with agalsidase beta is safe and effective in Japanese patients with Fabry disease. With regard to safety and efficacy, no differences were observed as compared to the caucasian population.

Expression of foreign proteins in Escherichia coli by fusing with an archaeal FK506 binding protein

Improper protein-folding often results in inclusion-body formation in a protein expression system using Escherichia coli. To express such proteins in the soluble fraction of E. coli cytoplasm, we developed an expression system by fusing the target protein with an archaeal FK506 binding protein (FKBP). It has been reported that an archaeal FKBP from a hyperthermophilic archaeon, Thermococcus sp. KS-1 (TcFKBP18), possesses not only peptidyl-prolyl cis-trans isomerase activity, but also chaperone-like activity to enhance the refolding yield of an unfolded protein by suppressing irreversible protein aggregation. To study the effect of this fusion strategy with FKBP on the expression of foreign protein in E. coli, a putative rhodanese (thiosulfate sulfurtransferase) from a hyperthermophilic archaeon and two mouse antibody fragments were used as model target proteins. When they were expressed alone in E. coli, they formed insoluble aggregates. Their genes were designed to be expressed as a fusion protein by connecting them to the C-terminal end of TcFKBP18 with an oligopeptide containing a thrombin cleavage site. By fusing TcFKBP18, the expression of the target protein in the soluble fraction was significantly increased. The percentage of the soluble form in the expressed protein reached 10-28% of the host soluble proteins. After purification and protease digestion of the expressed antibody fragment-TcFKBP18 fusion protein, the cleaved antibody fragment (single-chain Fv) showed specific binding to the antigen in ELISA. This indicated that the expressed antibody fragment properly folded to the active form.

In vitro study of encapsulation therapy for Fabry disease using genetically engineered CHO cell line

Fabry disease is an X-linked recessive disorder caused by a deficiency of the lysosomal hydrolase alpha-galactosidase A (alpha-gal). The deficiency of this enzyme leads to the systemic deposition of ceramide trihexoside (CTH) in various tissues and organs. Enzyme replacement using IV doses of recombinant human alpha-gal produced in CHO cells or in human fibroblasts is currently being evaluated in clinical trials as a potential therapy for this disease. However, it requires lifelong therapy involving a large amount of purified alpha-gal. As a novel approach for treatment of Fabry disease we used polymer encapsulated Chinese hamster ovary (CHO) cells genetically modified to express alpha-gal. The secreted high levels of alpha-gal passed through the semipermeable polymeric membrane. Using coculture system with Fabry fibroblasts, the secreted enzyme was taken up in cells, resulting in reduced accumulation of CTH in Fabry fibroblasts. This in vitro study demonstrated that an encapsulated alpha-gal-secreting cell line can be used to treat Fabry mice by transplantation in vivo. Judging from the protection against immune rejection by a semipermeable synthetic membrane, this novel approach may be applied to treat patients with Fabry disease and other lysosomal storage diseases.

Fishing for bioactive substances from scorpionfish and some sea urchins

Venom proteins from the dorsal spine of two scorpionfish, Hypodytes rubripinnis and Synanceia verrucosa were assayed for mitogenicity and cytotoxicity. The two venoms had both mitogenic and cytotoxic activity on murine splenocytes and murine P388 leukemic cells. In H. rubripinnis, the second gel chromatographic fraction showed cytotoxic activity on P388 leukemic cells. On native PAGE, the glycoprotein isolated by concavalin A sepharose chromatography appeared to have a molecular mass of 110 kDa. In addition, two D-galactose-binding lectins (SUL-I and SUL-II) and a heparin-binding lectin (TGL-I) were purified from the globiferous pedicellariae of the toxopneustid sea urchins, Toxopneustes pileolus and Tripneustes gratilla, respectively. SUL-I (Nakagawa et al., 1999a) had mitogenic activity and cytotoxic activity but SUL-II and TGL-I did not. SUL-I did not show sequence homology to SUL-II. A hemolytic lectin with a molecular mass of 29 kDa was isolated from the coelomic fluid of T. gratilla. The hemolytic activity of the lectin was dependent on Ca2+ concentration and inhibited by lactose. The present results suggest that some species of scorpionfish and sea urchins may be novel sources for biologically active substances such as anti-tumor compounds or new lectins.

Western blotting analysis of the beta-hexosaminidase alpha- and beta-subunits in cultured fibroblasts from cases of various forms of GM2 gangliosidosis

OBJECTIVES

The GM2 gangliosidoses are a group of genetic disorders caused by the accumulation of ganglioside GM2 in neuronal cells. We examined the alpha- and beta-subunits of beta-hexosaminidases by a non-radioisotopes detecting system to evaluate whether it was a useful method for understanding of the pathophysiologies of GM2 gangliosidoses.

MATERIALS AND METHODS

We investigated the alpha- and beta-subunits of beta-hexosaminidases in cultured fibroblasts from cases of various forms of GM2 gangliosidosis by means of Western blotting and a chemiluminescence detection system.

RESULTS

In a patient with infantile Tay-Sachs disease [HEXA genotype, Int5-SA(g-1-->t)/Int5-SA(g-1-->t)], the mature alpha-subunit was undetectable. In a patient with infantile Sandhoff disease (HEXB genotype, C534Y/C534Y), the mature beta-subunit was deficient. However, a small amount of the mature beta-subunit was detected in a patient with adult Sandhoff disease (HEXB genotype, R505Q(+I207V)/R505Q(+I207V)), which may have resulted in the residual enzyme activity and mild clinical course. Normal amounts of alpha- and beta-subunits were detected in a patient with GM2 activator deficiency.

CONCLUSION

This method is easy and sensitive for detecting target proteins, and is useful for clarification of the pathophysiologies of GM2 gangliosidoses.

Reduced beta-cell mass and expression of oxidative stress-related DNA damage in the islet of Japanese Type II diabetic patients

AIMS/HYPOTHESIS

We examined the pancreatic islet lesions in Japanese patients with Type II diabetes mellitus to determine if the damage was related to oxidative stress.

METHODS

Morphometric analyses were performed on immunostained sections of the tail portion of the pancreas from 14 diabetic and 15 non-diabetic patients. Amyloid deposition and oxidative stress-induced tissue damage were evaluated by Congo-red staining and immunostaining. Resistance to oxidative stress was assessed from immunostaining results for Cu, Zn-superoxide dismutase (SOD). Expression of (pro)insulin mRNA was assessed by in situ hybridisation.

RESULTS

The pancreas from diabetic patients had amyloid deposition in about 15 % of the islets, intensified reactions of 8-OHdG and HNE, as well as reduced expression of SOD. Islet volume density of beta cells and total beta-cell mass in the pancreas from diabetic patients were reduced by 22 % (p < 0.001) and 30 % (p < 0.05). Islet volume density and total mass of (pro)insulin mRNA-positive cells were similarly reduced in diabetic patients by 22 % (p < 0.001) and 39 % (p < 0.05), respectively. Islet volume density of A cells was increased by 20 % (p < 0.001) but total mass did not change. There were no changes in volume densities of islet, D and PP cells. Reduced beta-cell volume density correlated with increased positive staining of 8-OHdG.

CONCLUSION/INTERPRETATION

Japanese Type II diabetic patients show a reduction of beta-cell mass and evidence of increased oxidative stress-related tissue damage that is correlated with the extent of the beta-cell lesions.

Reduced beta-cell mass and expression of oxidative stress-related DNA damage in the islet of Japanese Type II diabetic patients

AIMS/HYPOTHESIS

We examined the pancreatic islet lesions in Japanese patients with Type II diabetes mellitus to determine if the damage was related to oxidative stress.

METHODS

Morphometric analyses were performed on immunostained sections of the tail portion of the pancreas from 14 diabetic and 15 non-diabetic patients. Amyloid deposition and oxidative stress-induced tissue damage were evaluated by Congo-red staining and immunostaining. Resistance to oxidative stress was assessed from immunostaining results for Cu, Zn-superoxide dismutase (SOD). Expression of (pro)insulin mRNA was assessed by in situ hybridisation.

RESULTS

The pancreas from diabetic patients had amyloid deposition in about 15 % of the islets, intensified reactions of 8-OHdG and HNE, as well as reduced expression of SOD. Islet volume density of beta cells and total beta-cell mass in the pancreas from diabetic patients were reduced by 22 % (p < 0.001) and 30 % (p < 0.05). Islet volume density and total mass of (pro)insulin mRNA-positive cells were similarly reduced in diabetic patients by 22 % (p < 0.001) and 39 % (p < 0.05), respectively. Islet volume density of A cells was increased by 20 % (p < 0.001) but total mass did not change. There were no changes in volume densities of islet, D and PP cells. Reduced beta-cell volume density correlated with increased positive staining of 8-OHdG.

CONCLUSION/INTERPRETATION

Japanese Type II diabetic patients show a reduction of beta-cell mass and evidence of increased oxidative stress-related tissue damage that is correlated with the extent of the beta-cell lesions.

Increasing the thermostability of Flavobacterium meningosepticum glycerol kinase by changing Ser329 to Asp in the subunit interface region

The thermostability enhancement of Flavobacterium meningosepticum glycerol kinase (FGK) by random mutagenesis in the subunit interface region was investigated. A single Escherichia coli transformant, which produced a more thermostable glycerol kinase than the parent enzyme, was obtained. The nucleotide sequence of the gene of the mutant enzyme (FGK2615) was determined, and the four amino acid replacements were identified as Glu327 to Asp, Ser329 to Asp, Thr330 to Ala and Ser334 to Lys. Although the properties of FGK2615 were fundamentally similar to those of the parent enzyme, the thermostability and Km for ATP had changed. The thermostability of FGK2615 was apparently increased; the temperature at which the enzyme activity is inactivated by 50% for a 30-min incubation of FGK2615 was determined to be 72.1 degrees C which was 3.1 degrees C higher than that of the parent FGK. Four additional mutants each having a single amino acid replacement (Glu327 to Asp, Ser329 to Asp, Thr330 to Ala and Ser334 to Lys) were prepared and their thermostability and Km for substrates were evaluated. The effect of the substitution of Ser329 to Asp is discussed.

A novel hyperthermophilic archaeal glyoxylate reductase from Thermococcus litoralis. Characterization, gene cloning, nucleotide sequence and expression in Escherichia coli

A novel NADH-dependent glyoxylate reductase has been found in a hyperthermophilic archaeon Thermococcus litoralis DSM 5473. This is the first evidence for glyoxylate metabolism and its corresponding enzyme in hyperthermophilic archaea. NADH-dependent glyoxylate reductase was purified approximately 560-fold from a crude extract of the hyperthermophile by five successive column chromatographies and preparative PAGE. The molecular mass of the purified enzyme was estimated to be 76 kDa, and the enzyme consisted of a homodimer with a subunit molecular mass of approximately 37 kDa. The optimum pH and temperature for enzyme activity were approximately 6.5 and 90 degrees C, respectively. The enzyme was extremely thermostable; the activity was stable up to 90 degrees C. The glyoxylate reductase catalyzed the reduction of glyoxylate and hydroxypyruvate, and the relative activity for hydroxypyruvate was approximately one-quarter that of glyoxylate in the presence of NADH as an electron donor. NADPH exhibited rather low activity as an electron donor compared with NADH. The Km values for glyoxylate, hydroxypyruvate, and NADH were determined to be 0.73, 1.3 and 0.067 mM, respectively. The gene encoding the enzyme was cloned and expressed in Escherichia coli. The nucleotide sequence of the glyoxylate reductase gene was determined and found to encode a peptide of 331 amino acids with a calculated relative molecular mass of 36,807. The amino-acid sequence of the T. litoralis enzyme showed high similarity with those of probable dehydrogenases in Pyrococcus horikoshii and P. abyssi. The purification of the enzyme from recombinant E. coli was much simpler compared with that from T. litoralis; only two steps of heat treatment and dye-affinity chromatography were needed.

Anti-apolipoprotein A-I autoantibody: characterization of monoclonal autoantibodies from patients with systemic lupus erythematosus

OBJECTIVE

The autoantibody to apolipoprotein A-I (apoA-I), a major constituent of high density lipoproteins (HDL), has been detected in sera of patients with systemic lupus erythematosus (SLE). We established a series of monoclonal anti-apoA-I antibodies (MAAI) from 2 patients with SLE and report the reactivities of MAAI with oxidized HDL, anionic substances, and blood coagulation factors.

METHODS

Peripheral blood B cells from patients with SLE were immortalized by Epstein-Barr virus, and B cells secreting anti-apoA-I antibodies (AAI) were fused with mouse myeloma cells. Six MAAI reactive with human apoA-I in both ELISA and immunoblotting analysis were established. The reactivities of MAAI with HDL, ssDNA and dsDNA, phospholipids such as cardiolipin (CL), and coagulation factors were examined by ELISA.

RESULTS

Although all MAAI bound effectively to apoA-I after the protein had been denatured and transferred to the filter membrane (in immunoblotting analyses), they bound less effectively to apoA-I present in HDL. Both oxidation of HDL in the presence of Mn2+ and an association of apoA-I with autoxidized trilinolein strongly enhanced the binding of MAAI to apoA-I, suggesting that MAAI recognize a defined region of apoA-I, which is exposed upon interacting with oxidatively modified lipids. MAAI showed a functional heterogeneity in their cross-reactivity with self-components: some MAAI were shown to cross-react with anionic substances such as CL and ssDNA, and one MAAI was shown to bind effectively to thrombin.

CONCLUSION

We identified a novel family of AAI that shows preferential binding to apoA-I in oxidatively modified HDL. These AAI are composed of antibodies with heterogeneous cross-reactivities to various self-components such as anionic phospholipids, ssDNA, and thrombin.

Existence of variant gamma delta T cells in Crohn's disease

BACKGROUND AND OBJECTIVES

gamma delta T cell populations are well-known for their unique distribution (e.g. intra-epithelial lymphocytes). Though their ligands play a major role in the immune response they have remained largely obscure. To shed light on this issue, we have analyzed in this study the complementarity determining region (CDR) 3 of the T cell receptor (TCR) V delta 2 chains. This provides an insight into the antigenic immune response in the intestinal mucosa in sickness and health.

METHODOLOGY

Total RNA was extracted from surgically resected intestinal mucosa of patients with Crohn's disease (CD) and controls. TCR V delta 2 cDNA was PCR-amplified using V delta 2 sense primer and C delta antisense primer. The PCR products were then subcloned in pUC18 plasmid. From each sample, 20 subclones were randomly selected and subjected to nucleotide sequence analysis.

RESULTS

Sequence analysis revealed that the CDR3 sequences of the TCR V delta 2 chains were unique to each individual. The evidence also showed a significant restriction of the junctional diversity of the TCR V delta 2 chains while no such restriction was found for CD.

CONCLUSIONS

The marked complexity of the TCR V delta 2 junctional sequences and the oligoclonality of the TCR V delta 2 genes in the control subjects are indicative of a positive selection and expansion of specific T cells in the normal, healthy condition. In CD patients, however, the expression of distinct, non-overlapping TCR V delta 2 clonotypes can be found, suggesting polyclonal activation of gamma delta T cells in the diseased colon of CD patients. These findings have led us to conclude that accumulation of multiple gamma delta T cell clonotypes may be involved in the pathogenesis of CD.

Purification, characterization, and application of a novel dye-linked L-proline dehydrogenase from a hyperthermophilic archaeon, Thermococcus profundus

The distribution of dye-linked L-amino acid dehydrogenases was investigated in several hyperthermophiles, and the activity of dye-linked L-proline dehydrogenase (dye-L-proDH, L-proline:acceptor oxidoreductase) was found in the crude extract of some Thermococcales strains. The enzyme was purified to homogeneity from a hyperthermophilic archaeon, Thermococcus profundus DSM 9503, which exhibited the highest specific activity in the crude extract. The molecular mass of the enzyme was about 160 kDa, and the enzyme consisted of heterotetrameric subunits (alpha(2) beta(2)) with two different molecular masses of about 50 and 40 kDa. The N-terminal amino acid sequences of the alpha-subunit (50-kDa subunit) and the beta-subunit (40-kDa subunit) were MRLTEHPILDFSERRGRKVTIHF and XRSEAKTVIIGGGIIGLSIAYNLAK, respectively. Dye-L-proDH was extraordinarily stable among the dye-linked dehydrogenases under various conditions: the enzyme retained its full activity upon incubation at 70 degrees C for 10 min, and ca. 40% of the activity still remained after heating at 80 degrees C for 120 min. The enzyme did not lose the activity upon incubation over a wide range of pHs from 4.0 to 10.0 at 50 degrees C for 10 min. The enzyme exclusively catalyzed L-proline dehydrogenation using 2,6-dichloroindophenol (Cl2Ind) as an electron acceptor. The Michaelis constants for L-proline and Cl2Ind were determined to be 2.05 and 0.073 mM, respectively. The reaction product was identified as Delta(1)-pyrroline-5-carboxylate by thin-layer chromatography. The prosthetic group of the enzyme was identified as flavin adenine dinucleotide by high-pressure liquid chromatography. In addition, the simple and specific determination of L-proline at concentrations from 0.10 to 2.5 mM using the stable dye-L-proDH was achieved.

Glutamate dehydrogenase from the aerobic hyperthermophilic archaeon Aeropyrum pernix K1: enzymatic characterization, identification of the encoding gene, and phylogenetic implications

NADP-dependent glutamate dehydrogenase (L-glutamate: NADP oxidoreductase, deaminating, EC 1.4.1.4) from the aerobic hyperthermophilic archaeon Aeropyrum pernix K1 (JCM 9820) was purified to homogeneity for characterization. The enzyme retained its full activity on heating at 95 degrees C for 30 min, and the maximum activity in L-glutamate deamination was obtained around 100 degrees C. The enzyme showed a strict specificity for L-glutamate and NADP on oxidative deamination and for 2-oxoglutarate and NADPH on reductive amination. The Km values for NADP, L-glutamate, NADPH, 2-oxoglutarate, and ammonia were 0.039, 3.3, 0.022, 1.7, and 83 mM, respectively. On the basis of the N-terminal amino acid sequence, the encoding gene was identified in the A. pernix K1 genome, cloned, and expressed in Escherichia coli. Analysis of the nucleotide sequence revealed an open reading frame of 1257 bp starting with a minor TTG codon and encoding a protein of 418 amino acids with a molecular weight of 46170. Phylogenetic analysis revealed that the glutamate dehydrogenase from A. pernix K1 clustered with those from aerobic Sulfolobus solfataricus, Sulfolobus shibatae, and anaerobic Pyrobaculum islandicum in Crenarchaeota, and it separated from another cluster of the enzyme from Thermococcales in Euryarchaeota. The branching pattern of the enzymes from A. pernix K1, S. solfataricus, S. shibatae, and Pb. islandicum in the phylogenetic tree coincided with that of 16S rDNAs obtained from the same organisms.

Biochemical characterization, cloning, and sequencing of ADP-dependent (AMP-forming) glucokinase from two hyperthermophilic archaea, Pyrococcus furiosus and Thermococcus litoralis

The ADP-dependent (AMP-forming) glucokinases from the hyperthermophilic archaea Pyrococcus furiosus and Thermococcus litoralis catalyze the phosphorylation of glucose using ADP as the essential phosphoryl group donor. Both enzymes were purified to homogeneity and characterized with regard to each other. The enzymes had similar enzymological properties as to substrate specificity, coenzyme specificity, optimum pH, and thermostability. However, a difference was observed in the subunit composition; while the T. litoralis enzyme is a monomer with a molecular mass of 52 kDa, the P. furiosus enzyme has a molecular mass of about 100 kDa and consists of two subunits with identical molecular masses of 47 kDa. The genes encoding these enzymes were cloned and sequenced. The gene for the P. furiosus enzyme contains an open reading frame for 455 amino acids with a molecular weight of 51,265, and that for the T. litoralis enzyme contains an open reading frame for 467 amino acids with a molecular weight of 53,621. About 59% similarity in amino acid sequence was observed between these two enzymes, whereas they did not show similarity with any ATP-dependent kinases that have been reported so far. In addition, two phosphate binding domains, and adenosine and glucose binding motifs commonly conserved in the eukaryotic hexokinase family were not observed.

Molecular and structural studies of Japanese patients with sialidosis type 1

To gain insight into the pathogenesis of sialidosis type 1, we performed molecular investigations of two unrelated Japanese patients. Both of them are compound heterozygotes for base substitutions of 649G-to-A and 727G-to-A, which result in amino acid alterations V217M and G243R, respectively. Using homology modeling, the structure of human lysosomal neuraminidase was constructed and the structural changes caused by these missense mutations were deduced. The predicted change due to V217M was smaller than that caused by G243R, the latter resulting in a drastic, widespread alteration. The overexpressed gene products containing these mutations had the same molecular weight as that of the wild type, although the amounts of the products were moderately decreased. A biochemical study demonstrated that the expressed neuraminidase containing a V217M mutation was partly transported to lysosomes and showed residual enzyme activity, although a G243R mutant was retained in the endoplasmic reticulum/Golgi area and had completely lost the enzyme activity. Considering the data, we surmise that the V217M substitution may be closely associated with the phenotype of sialidosis type 1 with a late onset and moderate clinical course.

Structural and functional study of K453E mutant protective protein/cathepsin A causing the late infantile form of galactosialidosis

To clarify the molecular basis of the late infantile form of galactosialidosis, we characterized a defective protective protein/cathepsin A (PPCA) gene product with the K453E mutation newly found in an Arabic patient with this disease. Immunocytochemical, expression, and metabolic studies revealed that the precursor PPCA was synthesized but not processed to the mature form, and it was degraded in the mutant. A structural model of the mutant PPCA was constructed by amino acid substitution of 453glutamic acid for lysine in the crystal structure of the wild type PPCA precursor reported. The results show that the K453E mutation is located at the dimer interface of the PPCA and reduces the hydrogen bond formation in the dimer. This structural change may cause instability of the PPCA dimer.

Angiokeratoma corporis diffusum associated with galactosialidosis

We describe a 34-year-old Japanese man with generalized angiokeratomas and various neurological symptoms since childhood. A number of reddish papules were scattered over his entire body and were especially numerous on his elbows, knees, penis and scrotum. An electron-microscopic study revealed a number of vacuoles in the cytoplasm of the vascular endothelial cells. This finding suggests that the angiokeratomas resulted from an injury of the endothelial cells due to the storage of metabolic material. A laboratory examination demonstrated a deficiency of both the beta-galactosidase and neuramidase activity in his leukocytes and fibroblasts. A restriction site analysis of PCR-amplified genomic DNA revealed that the patient had an mRNA splicing junction mutation at the 5' donor splice site of the exon 7/intron 7 junction in the protective protein gene.

Characterization of two alpha-galactosidase mutants (Q279E and R301Q) found in an atypical variant of Fabry disease

The mutant products Q279E ((279)Gln to Glu) and R301Q ((301)Arg to Gln) of the X-chromosomal inherited alpha-galactosidase (EC 3.2.1. 22) gene, found in unrelated male patients with variant Fabry disease (late-onset cardiac form) were characterized. In contrast to patients with classic Fabry disease, who have no detectable alpha-galactosidase activity, atypical variants have residual enzyme activity. First, the properties of insect cell-derived recombinant enzymes were studied. The K(m) and V(max) values of Q279E, R301Q, and wild-type alpha-galactosidase toward an artificial substrate, 4-methylumbelliferyl-alpha-D-galactopyranoside, were almost the same. In order to mimic intralysosomal conditions, the degradation of the natural substrate, globotriaosylceramide, by the alpha-galactosidases was analyzed in a detergent-free-liposomal system, in the presence of sphingolipid activator protein B (SAP-B, saposin B). Kinetic analysis revealed that there was no difference in the degradative activity between the mutants and wild-type alpha-galactosidase activity toward the natural substrate. Then, immunotitration studies were carried out to determine the amounts of the mutant gene products naturally occurring in cells. Cultured lymphoblasts, L-57 (Q279E) and L-148 (R301Q), from patients with variant Fabry disease, and L-20 (wild-type) from a normal subject were used. The 50% precipitation doses were 7% (L-57) and 10% (L-148) of that for normal lymphoblast L-20, respectively. The residual alpha-galactosidase activity was 3 and 5% of the normal level in L-57 and L-148, respectively. The quantities of immuno cross-reacting materials roughly correlated with the residual alpha-galactosidase activities in lymphoblast cells from the patients. Compared to normal control cells, fibroblast cells from a patient with variant Fabry disease, Q279E mutation, secreted only small amounts of alpha-galactosidase activity even in the presence of 10 mM NH(4)Cl. It is concluded that Q279E and R301Q substitutions do not significantly affect the enzymatic activity, but the mutant protein levels are decreased presumably in the ER of the cells.

Enzymatic corrections for cells derived from Fabry disease patients by a recombinant adenovirus vector

Fabry disease is an X-linked inherited metabolic disorder caused by a deficiency of alpha-galactosidase (alpha-gal), resulting in the accumulation of ceramide trihexoside (CTH) in body fluids and in many organs and tissues. We constructed a recombinant adenovirus with a human alpha-gal cDNA (AxCAG alpha-gal), and transfected this vector to skin fibroblasts from Fabry patients. Transfected cells expressed high amounts of alpha-gal in their cytoplasm, and a high level of alpha-gal activity was detected in the medium. The accumulated CTH in the fibroblasts disappeared 3 days after infection. The secreted alpha-gal also eliminated the accumulated CTH from uninfected patient's cells. The enzyme may be taken up through mannose-6-phosphate receptors, as the addition of mannose-6-phosphate to the medium completely inhibited the uptake of the enzyme. The infected cells continued to express alpha-gal for more than 10 days. These results suggest that AxCAG alpha-gal could be used as enzyme replacement gene therapy for Fabry disease.

Inhibition of progressive reduction of islet beta-cell mass in spontaneously diabetic Goto-Kakizaki rats by alpha-glucosidase inhibitor

The Goto-Kakizaki (GK) rat, an animal model of type 2 diabetes, exhibits mild hyperglycemia with a reduction of beta-cell mass. The mechanism for islet structural changes in this model and whether the changes are affected by metabolic control are not known. In the present study, we examined the process of islet changes in male GK rats aged 6, 8, 12, 24, and 36 weeks. Treatment effects with an alpha-glucosidase inhibitor (Voglibose; Takeda, Osaka, Japan) for 24 weeks (12 to 36 weeks of age) were also evaluated. The beta-cell mass increased until 8 weeks of age in both GK and control rats, but the increase was significantly (P < .01) smaller in GK rats versus at 8 weeks of age. Thereafter, the beta-cell mass decreased in GK rats, whereas it remained constant in controls. Voglibose treatment significantly (P < .01) inhibited the reduction of beta-cell mass in GK rats. Proliferative activity of beta cells as measured by bromodeoxyuridine (BrdU) uptake was significantly (P < .05) lower in GK rats versus control rats at 6 and 8 weeks, but the difference disappeared after 12 weeks of age, regardless of Voglibose treatment. The present study thus demonstrates a progressive loss of beta cells in GK rats that was mitigated by Voglibose treatment. We consider that the beta-cell loss in GK rats was due to an early impairment in proliferative activity and reduced survival. Voglibose did not appear to stimulate beta-cell proliferation, but exerted its effect via a reduction of hyperglycemia.

Endothelin-1 in the brain of patients with galactosialidosis: its abnormal increase and distribution pattern

Endothelin-1 is a peptidic substrate in vitro of lysosomal protective protein/cathepsin A (PPCA) with serine carboxypeptidase activity. Endothelin-1-specific immunoreactivity has been demonstrated to be markedly increased and distributed abnormally in the neurons and glial cells within autopsied brain regions, including the cerebellum, hippocampal formation, and spinal cord, of patients affected with galactosialidosis, a human PPCA deficiency. The genetic defect of the endothelin-1 degrading activity of PPCA is suggested to cause some of the neurological abnormalities of this disease.

Retrovirus-mediated transfer of human alpha-galactosidase A gene to human CD34+ hematopoietic progenitor cells

Fabry disease, caused by a deficiency of lysosomal enzyme alpha-galactosidase A (alpha-gal A), is one of the inherited disorders potentially treatable by gene transfer to hematopoietic stem cells. In this study, a high-titer amphotropic retroviral producer cell line, MFG-alpha-gal A, was established. CD34+ cells from normal umbilical cord blood were transduced by centrifugal enhancement. The alpha-gal A activity in transduced cells increased 3.6-fold above the activity in nontransduced cells. Transduction efficiency measured by PCR for the integrated alpha-gal A cDNA in CFU-GM colonies was in the range of 42-88% (average, 63%). The expression of functional enzyme in TFI erythroleukemia was sustained for as long as cells remained in culture (84 days) and for 28 days in LTC-IC cultures of CD34+ cells. The ability of the transduced CD34+ cells to secrete the enzyme and to correct enzyme-deficient Fabry fibroblasts was assessed by cocultivation of these cells. The enzyme was secreted into the medium from transduced CD34+ cells and taken up by Fabry fibroblasts through mannose 6-phosphate receptors. These findings suggest that genetically corrected hematopoietic stem/progenitor cells can be an enzymatic source for neighboring enzyme-deficient cells, and can potentially be useful for gene therapy of Fabry disease.

The NAD-dependent glutamate dehydrogenase from the hyperthermophilic archaeon Pyrobaculum islandicum: cloning, sequencing, and expression of the enzyme gene(1)

The NAD-dependent glutamate dehydrogenase (GluDH) gene from the hyperthermophilic archaeon Pyrobaculum islandicum was cloned and expressed in Escherichia coli. Analysis of the nucleotide sequence revealed an open reading frame of 1266 bp encoding a protein of 421 amino acids with a molecular weight of 46,905. In the alignment of the amino acid sequence with those of mesophilic Clostridium symbiosum NAD-dependent GluDH and hyperthermophilic NADP-dependent enzymes from Thermococcus profundus and Pyrococcus furiosus, substitutions in the residues involved in dinucleotide binding were observed. On the other hand, the residues involved in glutamate binding were well conserved. This is the first description of the primary structure of NAD-dependent GluDH in hyperthermophilic archaea.

Stable expression of protective protein/cathepsin A-green fluorescent protein fusion genes in a fibroblastic cell line from a galactosialidosis patient. Model system for revealing the intracellular transport of normal and mutated lysosomal enzymes

Fibroblastic cell lines derived from a galactosialidosis patient, stably expressing the chimaeric green fluorescent protein variant (EGFP) gene fused to the wild-type and mutant human lysosomal protective protein/cathepsin A (PPCA) cDNA, were first established as a model system for revealing the sorting and processing of lysosomal enzymes and for investigating the molecular bases of their deficiencies. In the cell line expressing the wild-type PPCA-EGFP chimaera gene (EGFP-PPwild), an 81 kDa form (27 kDa EGFP fused to the C-terminus of the 54 kDa PPCA precursor) was produced, then processed into the mature 32/20 kDa two-chain form free of the EGFP domain. The intracellular cathepsin A, alpha-N-acetylneuraminidase and beta-galactosidase activities, which are deficient in the parent fibroblastic cells, could also be significantly restored in the cells. In contrast with the uniform and strong fluorescence throughout the cytoplasm and nucleus in the mock-cell line expressing only EGFP cDNA, weak reticular and punctate fluorescence was distributed throughout the EGFP-PPwild cell line. Bafilomycin A1, a potent inhibitor of vacuolar ATPase and intracellular acidification, induced the distribution of Golgi-like perinuclear fluorescence throughout the living and fixed cells, in which only the 81 kDa product was detected. After removal of the agent, time-dependent transport of the chimaeric protein from the Golgi apparatus to the prelysosomal structure in living cells was monitored with a confocal laser scanning microscope system. Leupeptin caused the distribution of lysosome-like granular fluorescence throughout the cytoplasm in the fixed cells, although it was hardly observed in living cells. The latter agent also dose-dependently induced an increase in the intracellular amount of the 81 kDa product containing the EGFP domain and inhibited the restoration of cathepsin A activity in the EGFP-PPwild cells after the removal of bafilomycin A1. In parallel, both the mature two-chain form and PPCA function disappeared. These results suggested that the chimaera gene product was transported to acidic compartments (endosomes/lysosomes), where proteolytic processing of the PPCA precursor/zymogen, quenching of the fluorescence, and random degradation of the EGFP portion occurred. A cell line stably expressing a chimaeric gene with a mutant PPCA cDNA containing an A1184-->G (Y395C) mutation, commonly detected in Japanese severe early-infantile type of galactosialidosis patients, showed an endoplasmic reticulum (ER)-like reticular fluorescence pattern. The PPCA-immunoreactive gene product was hardly detected in this cell line. The mutant chimaeric product was suggested to be degraded rapidly in the ER before transport to post-ER compartments. A cell line expressing the chimaeric gene with a T746-->A (Y249N) PPCA mutation exhibited both ER-like reticular and granular fluorescence on the reticular structure that was stronger than that in the EGFP-PPwild cells. Some of them contained large fluorescent inclusion-body-like structures. The ineffectiveness of transport inhibitors in the distribution changes in the two mutant chimaeric proteins suggested that they were not delivered to acidic compartments. Therefore this expression system can possibly be applied to the direct analysis of the sorting defects of mutant gene products in living cells and will be useful for the molecular investigation of lysosomal diseases, including galactosialidosis.

Late endosomal membranes rich in lysobisphosphatidic acid regulate cholesterol transport

The fate of free cholesterol released after endocytosis of low-density lipoproteins remains obscure. Here we report that late endosomes have a pivotal role in intracellular cholesterol transport. We find that in the genetic disease Niemann-Pick type C (NPC), and in drug-treated cells that mimic NPC, cholesterol accumulates in late endosomes and sorting of the lysosomal enzyme receptor is impaired. Our results show that the characteristic network of lysobisphosphatidic acid-rich membranes contained within multivesicular late endosomes regulates cholesterol transport, presumably by acting as a collection and distribution device. The results also suggest that similar endosomal defects accompany the anti-phospholipid syndrome and NPC.

Missense mutations in the gp91-phox gene encoding cytochrome b558 in patients with cytochrome b positive and negative X-linked chronic granulomatous disease

Chronic granulomatous disease (CGD) is a disorder of host defense due to genetic defects of the superoxide (O2-) generating NADPH oxidase in phagocytes. A membrane-bound cytochrome b558, a heterodimer consisting of gp91-phox and p22-phox, is a critical component of the oxidase. The X-linked form of the disease is due to defects in the gp91-phox gene. We report here biochemical and genetic analyses of patients with typical and atypical X-linked CGD. Immunoblots showed that neutrophils from one patient had small amounts of p22-phox and gp91-phox and a low level of O2- forming oxidase activity, in contrast to the complete absence of both subunits in two patients with typical CGD. Using polymerase chain reactions (PCR) on cDNA and genomic DNA, we found novel missense mutations of gp91-phox in the two typical patients and a point mutation in the variant CGD, a characteristic common to two other patients with similar variant CGD reported previously. Spectrophotometric analysis of the neutrophils from the variant patient provided evidence for the presence of heme of cytochrome b558. Recently, we reported another variant CGD with similar amounts of both subunits, but without oxidase activity or the heme spectrum. A predicted mutation at amino acid 101 in gp91-phox was also confirmed in this variant CGD by PCR of the genomic DNA. These results on four patients, including those with two variant CGD, are discussed with respect to the missense mutated sites and the heme binding ligands in gp91-phox.

Expression of protective protein in human tissue

The authors investigated by immunohistochemistry the distribution of protective protein in human tissues. Immunoreactivity was observed in the cytoplasm, revealing a granular pattern and cell type specificity. The most intense staining was observed in the large neurons of brain, distal and collecting tubular cells of kidney, epithelial cells of bronchus, and Leydig cells of testis. In a patient with galactosialidosis type IIa, all these stains were absent. The neurons that were most strongly stained in the control group, such as the Betz cells, neurons in the basal forebrain, motor neurons in the cranial nerve nuclei, and ventral horn cells of the spinal cord, were markedly ballooned in the patient with galactosialidosis.

GM2 gangliosidosis AB variant: clinical and biochemical studies of a Japanese patient

OBJECTIVE

To determine the clinical features and biochemical basis of the first Japanese patient with the GM2 gangliosidosis AB variant.

METHODS

The clinical manifestations and laboratory findings in the patient were investigated. Cultured fibroblasts from the patient were analyzed by means of immunofluorescence staining with an anti-GM2 ganglioside monoclonal antibody and thin-layer chromatography and immunostaining. GM1 ganglioside catabolism in cultured cells was analyzed by pulse labeling, and the amount of GM2 activator in cells was determined by Western blot analysis. Gene analysis was performed according to standard protocols.

RESULTS

The patient showed progressive neurologic manifestations of quite early onset. Muscular weakness and hypotonia became evident by 1 month of age, and the patient then developed a startle reaction, severe psychomotor retardation, and myoclonic seizures. Immunocytochemical analysis clearly revealed the accumulation of GM2 ganglioside in cultured fibroblasts from the patient, and thin-layer chromatography confirmed it. Western blot and metabolic studies showed a complete deficiency of GM2 activator. Gene analysis did not reveal any mutations in the protein coding region of the GM2 activator gene.

CONCLUSION

The clinical features and biochemical basis of this Japanese patient with GM2 gangliosidosis AB variant were determined. Immunocytochemical analysis using cultured fibroblasts as samples is available for the diagnosis of this disease.

Urinary excretion of the vitronectin receptor (integrin alpha V beta 3) in patients with Fabry disease

A renal disorder is one of the important manifestations of Fabry disease, but the details of the pathogenesis have not been clarified yet. We examined the possibility that the vitronectin receptor (VNR, integrin alpha V beta 3), one of the integrins, is involved in the progression of the renal injury in Fabry disease. We measured the urinary excretion of beta 3 originating from VNR in Fabry patients by immunoblotting analysis and enzyme-linked immunosorbent assay (ELISA). Immunofluorescent microscopic analyses for VNR and globotriaosylceramide were performed on urinary sediments from Fabry patients. Furthermore, beta 3 and vitronectin in kidney tissues were analyzed immunohistochemically. Immunoblotting analysis and ELISA showed that the urinary excretion of beta 3 originating from VNR was significantly increased in the Fabry group compared with both the pathological and healthy control groups. Immunofluorescent microscopy revealed the expression of VNR and accumulation of globotriaosylceramide in urinary sediments from the Fabry patients. Increased expression of beta 3 was observed in glomerular epithelial cells, and in Bowman's capsular epithelial layer and tubular cells, and the amount of vitronectin was moderately increased in the kidney tissues from the Fabry patients. The urinary excretion of VNR was increased, and the expression of VNR was observed in Fabry kidney tissues. The expression of VNR may be involved in the progression of the renal injury in this disease.

Stabilizing effect of lysosomal beta-galactosidase on the catalytic activity of protective protein/cathepsin A secreted by human platelets

The 32/20-kDa two-chain form of protective protein/cathepsin A (CathA) secreted by human platelets was thermostable in the aggregation supernatant at acidic pH, but was denatured at neutral pH. Leupeptin partly protected the CathA against denaturation, which was not observed in the supernatant after depletion of the cosecreted lysosomal acid beta-galactosidase (beta-Gal) by affinity separation with p-aminophenylthiogalactose (PATG)-agarose beads even at pH 4.8. The purified recombinant human beta-Gal proteins, the 84-kDa precursor and 64-kDa mature-like enzyme (the tryptic product of the 84-kDa precursor), also protected the CathA against denaturation at neutral pH in part. Biospecific interaction analysis revealed that the CathA secreted by platelets dose dependently bound to the immobilized recombinant beta-Gal proteins. The association rate constant of CathA with the 64-kDa mature-like beta-Gal was 4.0 x 10(6) (M-1 s-1) at acidic pH, which was three times larger than that with the 84-kDa beta-Gal precursor. The calculated affinity constants for the enzyme molecules at acidic pH were approximately 1 x 10(9) (M-1), and those at neutral pH were two orders lower. These results first demonstrated that beta-Gal stabilizes the catalytic activity of CathA through direct binding in vitro. The affinity was shown to increase with removal of the carboxy-terminal domain of the beta-Gal precursor.

Two mutations remote from an exon/intron junction in the beta-hexosaminidase beta-subunit gene affect 3'-splice site selection and cause Sandhoff disease

Four unrelated Japanese patients with infantile Sandhoff disease (beta-hexosaminidase beta-subunit deficiency) have been studied for the molecular basis of their severe phenotype. Two patients had complex base substitutions; one patient was homoallelic for a triple mutation (P417L, K121R, and S255R) and the other was a compound heterozygote of a double (P417L and K121R) mutation and the triple mutation. K121R is known to be a functional polymorphism, while P417L (exon 11, +8 C-->T) generates predominantly an abnormally spliced mRNA at base +112 of exon 11 and has been described in two patients with a juvenile form of the disease. The mild phenotype is attributed to the presence of a small amount of normally spliced mRNA. S255R is a novel mutation without prior description in the literature. An expression study of the normally spliced cDNA with the double and the triple mutations gave about 70% and 30% of normal activity, respectively. This finding suggests that S255R further reduces the catalytic activity of the already below-threshold amount of normally spliced mRNA and accounts for the more severe phenotype in our patients. In the other two patients, a novel disease-causing base transition was found within intron 10, away from the intron/exon junction (-17 a-->g). This mutation caused abnormal 3' splicing at position -37 of intron 10, and no normally spliced product was detectable upon RT-PCR analysis. We noted an unusually low splice site score (61.8) for the exon 10/intron 11 junction and suspected that this might be partially responsible for the aberrant splicing in these mutations. To test this hypothesis, we constructed four chimeric cDNAs all with an additional intron 10 inserted and evaluated their splicing efficiency. They, respectively, had the normal sequence, P417L (exon 11, +8 C-->T), the intronic mutation (-17 a-->g), and the intronic mutation with an artificially engineered intron 10/exon 11 junction of a higher splice site score (85.1). Of the total transcripts, 67% and 32% were correctly spliced in the normal chimeric construct and P417L, respectively, while no normally spliced product was generated either in the chimeric construct with -17 a-->g or in that with a high splice site score. The sequence around the adenosine -17 residue upstream of the normal acceptor splice site in this report, UGCAAU (-21 to -16), matches the consensus branchpoint sequence YNYRAY (Y, pyrimidine; R, purine; N, any base) reported in the literature. The mutation in this study is most likely to abolish lariat formation because the artificial site of the high splice site score did not improve splicing efficiency.