The structural basis for the susceptibility of gangliosides to enzymatic degradation

The conformational properties of GM2, GalNacbeta-4(Neu5Acalpha-3) Galbeta-4Glcbeta-1Cer have been compared to those of 6'-GM2, in which the linkage between the GalNAc and Gal was altered from GalNacbeta-4Galbeta- to GalNacbeta-6Galbeta-, and to those of GD1a, Neu5Acalpha-3Galbeta-3GalNAcbeta-4(Neu5Acalpha-3 )Galbeta-4Glcbeta-1Cer, and GalNAc-GD1a. Our results revealed that unlike the compact and rigid oligosaccharide head group found in GM2, where the Neu5Ac and the GalNAc residues interact, the sugar chain of 6'-GM2 is in an open spatial arrangement, with the Neu5Ac no longer interacting with GalNAc, freely accessible to external interactions. The structure of GD1a can be regarded as that of GM2 with an extension of the terminal Neu5Acalpha-3Galbeta-disaccharide. The inner portion of GD1a is that of GM2 comprising the very rigid GalNAc-[Neu5Ac-]Gal trisaccharide. The terminal Neu5Ac-Gal linkage is flexible and fluctuates between two limiting conformations. In GalNAc-GD1a the outer sialic acid gains conformational rigidity due to the presence of the outer GalNAc in position 4 of galactose. This ganglioside has two 'core' GalNAc-[Neu5Ac-]Gal trisaccharide linked in tandem.

Structural basis for the resistance of Tay-Sachs ganglioside GM2 to enzymatic degradation

To understand the reason why, in the absence of GM2 activator protein, the GalNAc and the NeuAc in GM2 (GalNAcbeta1-->4(NeuAcalpha2-->3)Galbeta1-->4Glcbet a1-1'Cer) are refractory to beta-hexosaminidase A and sialidase, respectively, we have recently synthesized a linkage analogue of GM2 named 6'GM2 (GalNAcbeta1-->6(NeuAcalpha2-->3)Galbeta1-->4Glcbet a1-1'Cer). While GM2 has GalNAcbeta1-->4Gal linkage, 6'-GM2 has GalNAcbeta1-->6Gal linkage (Ishida, H., Ito, Y., Tanahashi, E., Li, Y.-T., Kiso, M., and Hasegawa, A. (1997) Carbohydr. Res. 302, 223-227). We have studied the enzymatic susceptibilities of GM2 and 6'GM2, as well as that of the oligosaccharides derived from GM2, asialo-GM2 (GalNAcbeta1-->4Galbeta1--> 4Glcbeta1-1'Cer) and 6'GM2. In addition, the conformational properties of both GM2 and 6'GM2 were analyzed using NMR spectroscopy and molecular mechanics computation. In sharp contrast to GM2, the GalNAc and the Neu5Ac of 6'GM2 were readily hydrolyzed by beta-hexosaminidase A and sialidase, respectively, without GM2 activator. Among the oligosaccharides derived from GM2, asialo-GM2, and 6'GM2, only the oligosaccharide from GM2 was resistant to beta-hexosaminidase A. Conformational analyses revealed that while GM2 has a compact and rigid oligosaccharide head group, 6'GM2 has an open spatial arrangement of the sugar units, with the GalNAc and the Neu5Ac freely accessible to external interactions. These results strongly indicate that the resistance of GM2 to enzymatic hydrolysis is because of the specific rigid conformation of the GM2 oligosaccharide.

Prevention of stroke in urban China: a community-based intervention trial

BACKGROUND AND PURPOSE

Stroke has been the second leading cause of death in large cities in China since the 1980s. Meanwhile, the prevalences of hypertension and smoking have steadily increased over the last 2 decades. Therefore, a community-based intervention trial was initiated in 7 Chinese cities in 1987. The overall goal of the study was to evaluate the effectiveness of an intervention aimed at reducing multiple risk factors for stroke. The primary study objective was to reduce the incidence of stroke by 25% over 3.5 years of intervention.

METHODS

In May 1987 in each of 7 the cities, 2 geographically separated communities with a registered population of about 10 000 each were selected as either intervention or control communities. In each community, a cohort containing about 2700 subjects (>/=35 years old) free of stroke was sampled, and a survey was administered to obtain baseline data and screen the eligible subjects for intervention. In each city, a program of treatment for hypertension, heart disease, and diabetes was instituted in the intervention cohort (n approximately 2700) and health education was provided to the full intervention community (n approximately 10 000). A follow-up survey was conducted in 1990. Comparisons of intervention and control cohorts in each city were pooled to yield a single summary.

RESULTS

A total of 18 786 subjects were recruited to the intervention cohort and 18 876 to the control cohort from 7 cities. After 3.5 years, 174 new stroke cases had occurred in the intervention cohort and 253 in the control cohort. The 3.5-year cumulative incidence of total stroke was significantly lower in the intervention cohort than the control cohort (0.93% versus 1.34%; RR=0.69; 95% CI, 0.57 to 0.84). The incidence rates of nonfatal and fatal stroke, as well as ischemic and hemorrhagic stroke, were significantly lower in the intervention cohort than the control cohort. The prevalence of hypertension increased by 4.3% in the intervention cohort and by 7.8% in the control cohort. The average systolic and diastolic blood pressures increased more in the control cohort than in the intervention cohort. Among hypertensive individuals in the intervention cohort, awareness of hypertension increased by 6.7% and the percentage of hypertensives who regularly took antihypertensive medication increased 13.2%. All of these indices became worse in the control cohort. The prevalence of heart diseases and diabetes increased significantly in the both cohorts (P<0.01). The prevalence of consumption of alcohol increased slightly, and that of smoking remained constant in both cohorts.

CONCLUSIONS

A community-based intervention for stroke reduction is feasible and effective in the cities of China. The reduction, due to the intervention, in the incidence of stroke in the intervention cohort was statistically significant after 3.5 years of intervention. The sharp reduction in the incidence of stroke may be due to the interventions having blunted the expected increase in hypertension that accompanies aging as well as to better and earlier treatment of hypertension, particularly borderline hypertension. Applied health education to all the residents of the community may have prevented some normotensive individuals from developing hypertension and improved overall health awareness and knowledge.

The 1.8 A structures of leech intramolecular trans-sialidase complexes: evidence of its enzymatic mechanism

Intramolecular trans-sialidase from leech (Macrobdella decora) is the first member of the sialidase superfamily found to exhibit strict specificity towards the cleavage of terminal Neu5Acalpha2-->3Gal linkage in sialoglycoconjugates. Its release of 2,7-anhydro-Neu5Ac instead of Neu5Ac indicates that it catalyzes an intramolecular trans-sialosyl reaction. Crystal structures of its complexes with an inactive substrate analogue 2-propenyl-Neu5Ac, and with the product 2,7-anhydro-Neu5Ac, have been determined to 1.8 A resolution. The boat conformation of the pyranose observed in the complexes supports the proposed enzymatic mechanism that O7 of an axial 6-glycerol group attacks the positively charged C2 of the intermediate. A generalized mechanism is proposed for the sialidase superfamily.

Structure of a Numb PTB domain-peptide complex suggests a basis for diverse binding specificity

The phosphotyrosine-binding (PTB) domain of Numb, a protein involved in asymmetric cell division, has recently been shown to bind to the adapter protein Lnx through an LDNPAY sequence, to the Numb-associated kinase (Nak) through a sequence that does not contain an NPXY motif and to GP(p)Y-containing peptides obtained from library screening. We show here that these diverse peptide sequences bind with comparable affinities to the Numb PTB domain at a common binding site on the surface of the protein. The NMR structure of the Numb PTB domain in complex with a GPpY-containing peptide reveals a novel mechanism of binding with the peptide in a helical turn that does not hydrogen bond to the PTB domain beta-sheet. These results suggest that PTB domains can potentially have multiple modes of peptide recognition and provide a structural basis from which the multiple functions of the Numb PTB domain during asymmetric cell division could arise.

Optimizing separation conditions for proteins and peptides using imaged capillary isoelectric focusing

Separation conditions for antibodies, glycoproteins and peptides were optimized to fully realize the potential of automated imaged capillary isoelectric focusing (imaged cIEF) for protein analysis. Two commercially available capillary coatings, polyacrylamide and fluorocarbon, were found to provide reproducible results for cIEF separations. Both coatings could last more than 100 runs under normal cIEF conditions. Up to 30 mM salts (Na+) could be added to samples to prevent protein precipitation before and during isoelectric focusing performed under imaged cIEF. Short analysis time of the imaged cIEF also aided in the prevention of protein precipitation. High current at the beginning of the focusing for samples in salt could be avoided by applying a voltage gradient. Additions of up to 6 M urea and 20% glycerol could enhance solubility of proteins and peptide. Imaged cIEF was applied to the quantitation of monoclonal antibodies.

In vitro maturation of follicular oocytes of the Giant Panda (Ailuropoda melanoleuca): a case report

The Giant Panda is an endangered species that would benefit from biotechnological assistance in reproduction. However, because there are only a few of these animals left in the world, scientists hesitate to use them for research procedures. We were fortunate to obtain ovaries from a Giant Panda that died of hepatic cirrhosis during the nonbreeding season. Oocytes were harvested within 4 h of death by dissecting the ovarian cortex in physiological saline and collecting the cumulus-oocyte complexes from the fluid, and then were classified into large (> 125 microns) and small (100 to 124 microns) follicular oocytes and placed in TCM199 supplemented with FSH (10 micrograms/mL) and LH (20 micrograms/mL). After culture for 22 h at 37 degrees C in air with 5% CO2, response was evaluated by growth of oocytes and presence of the first polar body. Of the 26 large follicular oocytes that were harvested, 12 were considered suitable for IVM, and 14 were degenerated, had a broken zona pellucida or had lost some cytoplasm. Of the 12 cultured oocytes, all grew to a mean diameter of 141.1(SD = +/- 6.7, n = 12), and 4 released the first polar body. None of the small follicular oocytes showed growth or other signs of maturation. We conclude from our preliminary results that it is possible to obtain functional Giant Panda oocytes from ovaries obtained post mortem during the nonbreeding season.

Hearing impairment among young Chinese in an urban area

To evaluate hearing levels among young Chinese in an urban area, audiometry was carried out in Jinan city, Shandong Province, China. The subjects were 442 healthy school children and students ranging in age from 6-19 y. All subjects were asked to complete a brief questionnaire on otological symptoms, personal histories and use of noisy playthings. Audiometric threshold testing was performed at the audiometric frequencies of 0.5, 1, 2, 4 and 8 kHz. Logistic regression analysis was used to analyse the items of personal histories related to hearing impairment. Forty-five subjects (10% of the subjects) were classified as abnormal. Nineteen ears of the abnormal subjects showed 4 kHz-dip and 38 ears showed high-frequency hearing impairment. Lower prevalence of hearing impairment was found when compared with young Chinese in a rural area (20%). The logistic regression analysis showed that head trauma may be the cause of hearing impairment among young Chinese in urban areas. Otological examinations for all children sustaining head trauma are recommended.

The crystal structure of an intramolecular trans-sialidase with a NeuAc alpha2-->3Gal specificity

BACKGROUND

Intramolecular trans-sialidase from leech (Macrobdella decora) is a unique enzyme which cleaves the terminal neuraminic acid (NeuAc) residue from sialoglycoconjugates, releasing 2, 7-anhydro-neuraminic acid (2,7-anhydro-NeuAc). It is the first enzyme found to exhibit strictly specific cleavage of NeuAc alpha2-->3Gal linkages in sialoglycoconjugates. The release of 2,7-anhydro-NeuAc instead of NeuAc implies a unique mechanism, in which the sialosyl linkage is transferred within the sialoglycoconjugate rather than hydrolyzed. The aims of the structural study were to gain structural insight into the strict specificity and unique mechanism of this unusual enzyme.

RESULTS

. The 2.0 A crystal structure of recombinant leech intramolecular trans-sialidase has been solved by multiple isomorphous replacement. The 1.8 A structure of the enzyme in complex with 2-deoxy-2, 3-didehydro-NeuAc was also solved. The refined model comprising residues 81-769 has a catalytic beta-propeller domain (C), a N-terminal lectin-like domain (II) and an irregular beta-stranded domain (III) inserted into the catalytic domain. The structure reveals several possible carbohydrate-binding features: domain II has a concave face, like that of other sialidases, and there is a suitable surface charge distribution at the domain III-C interface.

CONCLUSIONS

Structural comparisons showed closer evolutionary relationships to bacterial sialidases than to viral neuraminidases. Mainchain and sidechain atoms around Thr593 make the glycerol-binding pocket incapable of accommodating an extended equatorial 6-glycerol group, implying that the 6-glycerol group of the reaction intermediate may occupy an axial position, which is also required by the catalytic mechanism. The steric hindrance introduced by the bulky sidechain of Trp734 above the 2-carboxylate group may explain the lack of water involvement in the cleavage reaction and the substrate specificity.

Antibodies to GT1a ganglioside in patients with Guillain-Barré syndrome

Serum antibodies from 8 (13%) of 62 patients with the acute Guillain-Barré syndrome (GBS) and 1 of 3 patients with the Miller Fisher syndrome (MFS) recognized a minor ganglioside in bovine and human brain trisialoganglioside fractions. The ganglioside antigen migrated between GD1a and GD1b on thin-layer chromatograms. The structure of this ganglioside was established to be GT1a by thin-layer chromatography blotting and mass spectrometry. GT1a a ganglioside was also detected in human and bovine peripheral nerves by thin-layer chromatogram immunostaining. Serum from the GBS patients had IgM, IgG, or IgA antibodies against GT1a detectable by enzyme-linked immunosorbent assay (ELISA). Serum from the MFS patient also had elevated levels of IG against GT1a. None of the sera from 43 patients with other neurological diseases or from 24 healthy controls reacted with GT1a. Sera from 6 of 8 GBS patients with anti-Gt1a antibodies also reacted with GQ1b. There was no difference in the incidence of anti-GT1a immunoglobulins in acute GBS patients with or without oculomotor abnormalities. Levels of anti-GT1a antibodies correlated temporally wit clinical symptoms in GBS patients. Although the incidence of dysphagia was slightly higher in GBS patients with anti-GT1a antibodies than in those without, the number of patients studied may have been too small to detect an association between anti-GT1a antibodies and an a specific clinical variant of GBS. Our data demonstrate that a proportion of GBS patients have antibodies against GT1a ganglioside and suggest that these antibodies may play a role in the pathogenesis of neuropathy in GBS.

Specificity of mouse GM2 activator protein and beta-N-acetylhexosaminidases A and B. Similarities and differences with their human counterparts in the catabolism of GM2

Tay-Sachs disease, an inborn lysosomal disease featuring a buildup of GM2 in the brain, is caused by a deficiency of beta-hexosaminidase A (Hex A) or GM2 activator. Of the two human lysosomal Hex isozymes, only Hex A, not Hex B, cleaves GM2 in the presence of GM2 activator. In contrast, mouse Hex B has been reported to be more active than Hex A in cleaving GM2 (Burg, J., Banerjee, A., Conzelmann, E., and Sandhoff, K. (1983) Hoppe Seyler's Z. Physiol. Chem. 364, 821-829). In two independent studies, mice with the targeted disruption of the Hexa gene did not display the severe buildup of brain GM2 or the concomitant abnormal behavioral manifestations seen in human Tay-Sachs patients. The results of these two studies were suggested to be attributed to the reported GM2 degrading activity of mouse Hex B. To clarify the specificity of mouse Hex A and Hex B and to better understand the observed results of the mouse model of Tay-Sachs disease, we have purified mouse liver Hex A and Hex B and also prepared the recombinant mouse GM2 activator. Contrary to the findings of Burg et al., we found that the specificities of mouse Hex A and Hex B toward the catabolism of GM2 were not different from the corresponding human Hex isozymes. Mouse Hex A, but not Hex B, hydrolyzes GM2 in the presence of GM2 activator, whereas GM2 is refractory to mouse Hex B with or without GM2 activator. Importantly, we found that, in contrast to human GM2 activator, mouse GM2 activator could effectively stimulate the hydrolysis of GA2 by mouse Hex A and to a much lesser extent also by Hex B. These results provide clear evidence on the existence of an alternative pathway for GM2 catabolism in mice by converting GM2 to GA2 and subsequently to lactosylceramide. They also provide the explanation for the lack of excessive GM2 accumulation in the Hexa gene-disrupted mice.

Brownian dynamics study of ion transport in the vestibule of membrane channels

Brownian dynamics simulations have been carried out to study the transport of ions in a vestibular geometry, which offers a more realistic shape for membrane channels than cylindrical tubes. Specifically, we consider a torus-shaped channel, for which the analytical solution of Poisson's equation is possible. The system is composed of the toroidal channel, with length and radius of the constricted region of 80 A and 4 A, respectively, and two reservoirs containing 50 sodium ions and 50 chloride ions. The positions of each of these ions executing Brownian motion under the influence of a stochastic force and a systematic electric force are determined at discrete time steps of 50 fs for up to 2.5 ns. All of the systematic forces acting on an ion due to the other ions, an external electric field, fixed charges in the channel protein, and the image charges induced at the water-protein boundary are explicitly included in the calculations. We find that the repulsive dielectric force arising from the induced surface charges plays a dominant role in channel dynamics. It expels an ion from the vestibule when it is deliberately put in it. Even in the presence of an applied electric potential of 100 mV, an ion cannot overcome this repulsive force and permeate the channel. Only when dipoles of a favorable orientation are placed along the sides of the transmembrane segment can an ion traverse the channel under the influence of a membrane potential. When the strength of the dipoles is further increased, an ion becomes detained in a potential well, and the driving force provided by the applied field is not sufficient to drive the ion out of the well. The trajectory of an ion navigating across the channel mostly remains close to the central axis of the pore lumen. Finally, we discuss the implications of these findings for the transport of ions across the membrane.

Synthesis of aryl 3'-sulfo-beta-lactosides as fluorogenic and chromogenic substrates for ceramide glycanases

We have previously reported that 4-methylumbelliferyl 6'-O-benzyl-beta-lactoside (2) is a useful substrate for a fluorometric assay of ceramide glycanase (CGase) (L.-X. Wang, N. V. Pavlova, S.-C. Li, Y.-T. Li and Y. C. Lee, Glycoconjugate J., 13 (1996) 359-365). The introduction of a 6-O-benzyl group at the terminal Gal efficiently protected the substrate from its hydrolysis by exo-galactosidase, permitting the assay of CGase in crude biological materials. However, a drawback of this substrate is its low water-solubility and relatively high Km (at a mM level). Introduction of a sulfate group into 4-methylumbelliferyl beta-lactoside (1) led to the formation of 4-methylumbelliferyl 3'-O-sulfo-beta-lactoside (3), which was found to be a more effective substrate than 2. Moreover, the presence of a 3'-O-sulfate group not only increases the water solubility tremendously, but also protects the substrate from cleavage by exo-beta-galactosidase as the 6'-O-benzyl group in 2 does. In addition to the fluorogenic substrate (3), two sulfated chromogenic substrates, N-tetradecanoyl-4-O(3'-sulfo-beta-lactosyl)-3-nitro-L-tyrosine methyl ester (9) and 2-N-(tetradecanoylamino)-4-nitro-phenyl 3'-sulfo-beta-lactoside (12), were synthesized and their suitability for a photometric assay of CGase was evaluated. Substrates 9 and 12, with a long fatty acid chain attached to the aglycon part, have a Km value close to that of the natural substrate GM1 (at a microM level).

Malignant tumors in the rectum simulating solitary rectal ulcer syndrome in endoscopic biopsy specimens

Patients with solitary rectal ulcer syndrome (SRUS) frequently present with a mass that can be misinterpreted as cancer. In contrast, the occurrence and characteristics of SRUS-like histopathology produced by underlying malignancy have not been reported in detail. We report seven patients whose rectal mass that was induced by infiltrating carcinoma showed only histopathologic changes of SRUS on initial mucosal biopsy specimens. Carcinoma was evident in subsequent specimens after one to five repeat biopsies with delay in diagnosis from 1 week to 18 months in six patients. In one patient, infiltrating carcinoma was suggested on the first biopsy specimen by immunohistochemistry for cytokeratin. Three of the patients had primary rectal adenocarcinoma, two had metastatic carcinoma from stomach or ovary, and two had direct invasion of anal squamous cell carcinoma or prostatic adenocarcinoma. We conclude that the histopathology of SRUS may occasionally represent a characteristic but nonspecific mucosal reactive change to a deeper seated malignancy. The terminology "solitary rectal ulcer syndrome/mucosal prolapse changes" with a cautionary note may be useful for reporting biopsy results to emphasize the possibility of underlying primary or metastatic malignancy in the differential diagnosis.

alpha-KDOase activity in oyster and synthesis of alpha- and beta-4-methylumbelliferyl ketosides of 3-deoxy-D-manno-octulosonic acid

Although alpha- and beta-linked 3-deoxy-D-manno-octulosonic acid (KDO) is found in lipopolysaccharides (LPSs) of Gram-negative bacteria, capsular polysaccharides of microorganisms, and plants, very little is known about its degradation. Using both thin-layer chromatography and the periodate-thiobarbituric acid reaction, we found that the hepatopancreas of oyster (Crassostrea virginica) contained an enzyme (alpha-KDOase) capable of releasing alpha-linked KDO from LPSs. To facilitate the studies of alpha-KDOase, we have carried out the synthesis of 4-methylumbelliferyl-alpha-KDO (alpha-KDO-MU) by conjugating the glycosyl chloride of the per-O-acetylated methylester of KDO with methylumbelliferone by the SN2 type reaction and the catalyzed phase-transfer. In both cases, the beta-anomer was obtained as the major product with a yield of about 80%, whereas the yield of alpha-anomer was only about 7%. Attempts to increase the yield of alpha-anomer were not successful. alpha-KDO-MU was used as substrate to follow the purification of alpha-KDOase from oyster hepatopancreas. The pH optimum for oyster alpha-KDOase was determined to be 4.5 using Re-LPS as substrate and 3.0 using alpha-KDO-MU as substrate. The enzyme was found to be stable in the pH range of 3-8. This enzyme released KDO from different LPSs, including Re-LPS from Escherichia coli and Salmonella minnesota, Rd-LPS from S. minnesota, and de-O-acyl-Re-LPS (Kiang, J., Szu, S. C., Wang, L.X., Tang, M., and Lee, Y. C. (1997) Anal. Biochem. 245, 97-101).

High-affinity binding of the Drosophila Numb phosphotyrosine-binding domain to peptides containing a Gly-Pro-(p)Tyr motif

The phosphotyrosine-binding (PTB) domain is a recently identified protein module that has been characterized as binding to phosphopeptides containing an NPXpY motif (X = any amino acid). We describe here a novel peptide sequence recognized by the PTB domain from Drosophila Numb (dNumb), a protein involved in cell fate determination and asymmetric cell division during the development of the Drosophila nervous system. Using a Tyr-oriented peptide library to screen for ligands, the dNumb PTB domain was found to bind selectively to peptides containing a YIGPYphi motif (phi represents a hydrophobic residue). A synthetic peptide containing this sequence bound specifically to the isolated dNumb PTB domain in solution with a dissociation constant (Kd) of 5.78 +/- 0.74 microM. Interestingly, the affinity of this peptide for the dNumb PTB domain was increased (Kd = 1.41 +/- 0.10 microM) when the second tyrosine in the sequence was phosphorylated. Amino acid substitution studies of the phosphopeptide demonstrated that a core motif of sequence GP(p)Y is required for high-affinity binding to the dNumb PTB domain. Nuclear magnetic resonance experiments performed on isotopically labeled protein complexed with either Tyr- or pTyr-containing peptides suggest that the same set of amino acids in the dNumb PTB domain is involved in binding both phosphorylated and nonphosphorylated forms of the peptide. The in vitro selectivity of the dNumb PTB domain is therefore markedly different from those of the Shc and IRS-1 PTB domains, in that it interacts preferentially with a GP(p)Y motif, rather than NPXpY, and does not absolutely require ligand phosphorylation for binding. Our results suggest that the PTB domain is a versatile protein module, capable of exhibiting varied binding specificities.

TWH regulates the development of subsets of spinal cord neurons

Thymocyte winged helix (TWH) is a putative transcription factor expressed in the developing neural tube. At midgestation, TWH expression identifies subsets of spinal cord motor neurons and interneurons. TWH-expressing motor neurons were restricted to specific spinal cord levels, distinguishing motor neurons at lumbar from those at cervical levels. To understand the developmental role of TWH, we replaced the TWH gene with the lacZ reporter gene and generated mice with a homozygous disruption of the TWH gene. TWH(-/-) mutant mice had increased perinatal mortality, retarded postnatal growth, and motor weakness. The TWH(-/-) mutation resulted in alterations in the sizes and position of different neuronal populations. Our results demonstrate that TWH plays a critical role in neuronal development and suggest that TWH regulates the early differentiation of neural progenitors.

Crystallization and preliminary X-ray characterization of GM2-activator protein

G(M2) activator protein is a glycolipid transfer protein cofactor necessary for the hydrolytic degradation of G(M2) ganglioside by beta-hexosaminidase A. Its absence in human tissue results in symptoms of type AB Tay-Sachs disease. The protein prepared by recombinant techniques using an E. coli expression system, has been crystallized by the vapor-diffusion technique. The crystals are well ordered and belong to the orthorhombic space group P2(1)2(1)2(1). The unit-cell dimensions are a = 42.40, b = 39.82, c = 113.61 A. One molecule is contained in the asymmetric unit.

Structural organization and expression of the gene for the mouse GM2 activator protein

The GM2 activator protein is an essential component for the degradation of GM2 ganglioside by hexosaminidase A in vivo. Mutations in the human gene coding for the GM2 activator protein cause the AB variant of GM2-gangliosidosis, a condition that is clinically indistinguishable from Tay-Sachs disease. To understand better factors affecting the expression of the GM2 activator protein gene (Gm2a) in mouse tissues, we have determined its exon-intron organization and analyzed its promoter region. Gm2a is about 14 kb, has four exons, and the 5' flanking region contains a CAAT box, Sp1 binding sites, AP-1, AP-2 sites, and a pair of IRE sites. A 1.2-kb fragment upstream from the initiation codon was shown to have promoter activity in NIH 3T3 cells. Similarities between the elements present in Gm2a and Hexa promoters might in part explain their similar expression patterns in mouse tissues. The different levels of GM2 activator protein mRNA in liver, kidney, brain, and testis are not owing to the use of different transcription start sites, because a single start site was found 50 bp upstream from the initiation codon in each these tissues. Northern blot analysis demonstrated variation in the GM2 activator protein mRNA expression during mouse development. Gm2a was mapped to Chromosome (Chr) 11, where it co-segregated with Csfgm.

Structural organization and expression of the gene for the mouse GM2 activator protein

The GM2 activator protein is an essential component for the degradation of GM2 ganglioside by hexosaminidase A in vivo. Mutations in the human gene coding for the GM2 activator protein cause the AB variant of GM2-gangliosidosis, a condition that is clinically indistinguishable from Tay-Sachs disease. To understand better factors affecting the expression of the GM2 activator protein gene (Gm2a) in mouse tissues, we have determined its exon-intron organization and analyzed its promoter region.Gm2a is about 14 kb, has four exons, and the 5' flanking region contains a CAAT box, Spl binding sites, AP-1, AP-2 sites, and a pair of IRE sites. A 1.2-kb fragment upstream from the initiation codon was shown to have promoter activity in NIH 3T3 cells. Similarities between the elements present in Gm2a and Hexa promoters might in part explain their similar expression patterns in mouse tissues. The different levels of GM2 activator protein mRNA in liver, kidney, brain, and testis are not owing to the use of different transcription start sites, because a single start site was found 50 bp upstream from the initiation codon in each these tissues. Northern blot analysis demonstrated variation in the GM2 activator protein mRNA expression during mouse development. Gm2a was mapped to Chromosome (Chr) 11, where it co-segregated with Csfgm.

Comparison of methods for measurement of apolipoprotein B and cholesterol in low-density lipoproteins

We describe a new method for the direct measurement of LDL-apolipoprotein (apo) B by using a commercial kit that isolates LDL by immunoseparation. We evaluated immunoseparation of LDL for apo B and cholesterol measurement in 46 dyslipidemic patients with LDL-cholesterol (LDL-C) between 1.5 and 8.2 mmol/L, 11 of whom had plasma triglyceride (TG) concentrations >4.0 mmol/L. There was a reasonable correlation (r = 0.94, n = 40) between LDL-apo B obtained after immunoseparation and d >1.006 kg/L apo B obtained after ultracentrifugation. LDL-C by the immunoseparation method also correlated well (r = 0.98, n = 46) with the d >1.006 kg/L cholesterol after ultracentrifugation. These results show that immunoseparation can be used to determine LDL-apo B, even in hypertriglyceridemic samples. This method may provide a quick and simple alternative for the identification of hyperapobetalipoproteinemia, even when TG concentrations are high.

Interaction of GM2 activator protein with glycosphingolipids

GM2 activator protein is a protein cofactor that has been shown to stimulate the enzymatic hydrolysis of both GalNAc and NeuAc from GM2 (Wu, Y. Y., Lockyer, J. M., Sugiyama, E., Pavlova, N.V., Li, Y.-T., and Li, S.-C. (1994) J. Biol. Chem. 269, 16276-16283). To understand the mechanism by which GM2 activator stimulates the hydrolysis of GM2, we examined the interaction of this activator protein with GM2 as well as with other glycosphingolipids by TLC overlay and Sephacryl S-200 gel filtration. The TLC overlay analysis unveiled the binding specificity of GM2 activator, which was not previously revealed. Under the conditions optimal for the activator protein to stimulate the hydrolysis of GM2 by beta-hexosaminidase A, GM2 activator was found to bind avidly to acidic glycosphingolipids, including gangliosides and sulfated glycosphingolipids, but not to neutral glycosphingolipids. The gangliosides devoid of sialic acids, such as asialo-GM1 and asialo-GM2, and the GM2 derivatives whose carboxyl function in the NeuAc had been modified by methyl esterification or reduction, were only very weakly bound to GM2 activator. These results indicate that the negatively charged sugar residue or sulfate group in gangliosides is one of the important sites recognized by GM2 activator. For comparison, we also studied in parallel the complex formation between glycosphingolipids and saposin B, a separate activator protein with broad specificity to stimulate the hydrolysis of various glycosphingolipids. We found that saposin B bound to neutral glycosphingolipids and gangliosides equally well, and there was an exceptionally strong binding to sulfatide. In contrast to previous reports, we found that GM2 activator formed complexes with GM2 and other gangliosides in different proportions depending on the ratio between the activator protein and the ganglioside in the incubation mixture prior to gel filtration. We were not able to detect the specific binding of GM2 activator to GM2 when GM2 was mixed with GM1 or GM3. Thus, the specificity or the mode of action of GM2 activator cannot be simply explained by its interaction with glycosphingolipids based on complex formation. The binding of GM2 activator to a wide variety of negatively charged glycosphingolipids may indicate that this activator protein has functions other than assisting the enzymatic hydrolysis of GM2.

Characterization of the phosphotyrosine-binding domain of the Drosophila Shc protein

The phosphotyrosine-binding (PTB) domain of Drosophila Shc (dShc) binds in vitro to phosphopeptides containing the sequence motif NPXpY, and physically associates with the activated Drosophila epidermal growth factor receptor homologue (DER) in vivo. The structural elements, specificity and binding kinetics of the dShc PTB domain have now been characterized. The dShc PTB domain appeared similar to the insulin-like receptor substrate-1 PTB domain in secondary structure as suggested by Fourier transform infrared spectroscopy. Surface plasmon resonance measurements indicated that the dShc PTB domain bound with high affinity to phosphopeptides (Der) derived from the Tyr1228 site of the DER receptor. The kinetics of the dShc PTB domain-Der phosphopeptide interaction differed from those of a typical SH2 domain-ligand interaction, in that the PTB domain displayed slower on/off rates. Competition binding assays using truncated versions of the Der peptides revealed that high affinity binding to the dShc PTB domain requires, in addition to the NPXpY motif, the presence of hydrophobic residues at both positions -5 and -7 relative to phosphotyrosine. The dShc PTB domain showed a similar binding specificity to the human Shc (hShc) PTB domain, but subtle differences were noted; such that the hShc PTB domain bound preferentially to a phosphopeptide from the mammalian nerve growth factor receptor, whereas the dShc PTB domain bound preferentially to phosphopeptides from the Drosophila DER receptor. The invertebrate dShc PTB domain therefore possesses a binding specificity for tyrosine-phosphorylated peptides that is optimally suited for recognition of the activated DER receptor.

Hearing impairment among young Chinese in a rural area

To evaluate hearing levels in Chinese young people, audiometry was carried out at a rural village in Shandong Prefecture. The subjects were 282 healthy school children and students ranging in age from 7-17 y. All subjects were asked to complete a brief questionnaire on otological symptoms, personal histories and use of noisy playthings. Audiometric threshold testing was performed at the audiometric frequencies of 0.5, 1, 2, 4 and 8 kHz. Cluster analysis was used to estimate the associations between questions in the questionnaire and hearing impairment. Fifty-six subjects (20% subjects) were excluded from the normal groups. Twenty-two ears of the excluded subjects showed 4 kHz-dip and 38 ears showed high frequency hearing loss. An increased prevalence of hearing impairment was found when compared with young Japanese (1% from the nationwide school health survey) and with young Chinese in Shandong Prefecture (0.5%). In the questionnaire, 4 questions on dizziness, head trauma, aminoglycoside administration, and suspicion of Meniere's syndrome, were included in the cluster of hearing impairment. The cause of this hearing impairment was proposed to be the potentiating effects of aminoglycoside antibiotics and exposure to noise.