Isolation of human glycogen branching enzyme cDNAs by screening complementation in yeast

Glycogen metabolism and structure: A review

Glycogen is a glucose polymer that plays a crucial role in glucose homeostasis by functioning as a short-term energy storage reservoir in animals and bacteria. Abnormalities in its metabolism and structure can cause several problems, including diabetes, glycogen storage diseases (GSDs) and muscular disorders. Defects in the enzymes involved in glycogen synthesis or breakdown, resulting in either excessive accumulation or insufficient availability of glycogen in cells seem to account for the most common pathogenesis. This review discusses glycogen metabolism and structure, including molecular architecture, branching dynamics, and the role of associated components within the granules. The review also discusses GSD type XV and Lafora disease, illustrating the broader implications of aberrant glycogen metabolism and structure. These conditions also impart information on important regulatory mechanisms of glycogen, which hint at potential therapeutic targets. Knowledge gaps and potential future research directions are identified.

WTAP/IGF2BP3-mediated GBE1 expression accelerates the proliferation and enhances stemness in pancreatic cancer cells via upregulating c-Myc

BACKGROUND

Pancreatic cancer (PC) is one of the most malignant cancers with highly aggressiveness and poor prognosis. N6-methyladenosine (m6A) have been indicated to be involved in PC development. Glucan Branching Enzyme 1 (GBE1) is mainly involved in cell glycogen metabolism. However, the function of GBE1 and Whether GBE1 occurs m6A modification in PC progression remains to be illustrated.

METHODS

The clinical prognosis of GBE1 was analyzed through online platform. The expression of GBE1 was obtained from online platform and then verified in normal and PC cell lines. Lentivirus was used to generated GBE1 stable-overexpression or knockdown PC cells. Cell Counting Kit (CCK-8), colony formation assay, sphere formation assay and flow cytometry assay were conducted to analyze cell proliferation and stemness ability in vitro. Subcutaneous and orthotopic mouse models were used to verify the function of GBE1 in vivo. RNA immunoprecipitation (RIP) assay, RNA stability experiment and western blots were conducted to explore the molecular regulation of GBE1 in PC.

RESULTS

GBE1 was significantly upregulated in PC and associated with poor prognosis of PC patients. Functionally, GBE1 overexpression facilitated PC cell proliferation and stemness-like properties, while knockdown of GBE1 attenuated the malignancy of PC cells. Importantly, we found the m6A modification of GBE1 RNA, and WTAP and IGF2BP3 was revealed as the m6A regulators to increase GBE1 mRNA stability and expression. Furthermore, c-Myc was discovered as a downstream gene of GBE1 and functional rescue experiments showed that overexpression of c-Myc could rescue GBE1 knockdown-induced PC cell growth inhibition.

CONCLUSIONS

Our study uncovered the oncogenic role of GBE1/c-Myc axis in PC progression and revealed WTAP/IGF2BP3-mediated m6A modification of GBE1, which highlight the potential application of GBE1 in the targeted therapy of PC.

Severe neuromuscular forms of glycogen storage disease type IV: Histological, clinical, biochemical, and molecular findings in a large French case series

Glycogen storage disease type IV (GSD IV), also called Andersen disease, or amylopectinosis, is a highly heterogeneous autosomal recessive disorder caused by a glycogen branching enzyme (GBE, 1,4-alpha-glucan branching enzyme) deficiency secondary to pathogenic variants on GBE1 gene. The incidence is evaluated to 1:600 000 to 1:800 000 of live births. GBE deficiency leads to an excessive deposition of structurally abnormal, amylopectin-like glycogen in affected tissues (liver, skeletal muscle, heart, nervous system, etc.). Diagnosis is often guided by histological findings and confirmed by GBE activity deficiency and molecular studies. Severe neuromuscular forms of GSD IV are very rare and of disastrous prognosis. Identification and characterization of these forms are important for genetic counseling for further pregnancies. Here we describe clinical, histological, enzymatic, and molecular findings of 10 cases from 8 families, the largest case series reported so far, of severe neuromuscular forms of GSD IV along with a literature review. Main antenatal features are: fetal akinesia deformation sequence or arthrogryposis/joint contractures often associated with muscle atrophy, decreased fetal movement, cystic hygroma, and/or hydrops fetalis. If pregnancy is carried to term, the main clinical features observed at birth are severe hypotonia and/or muscle atrophy, with the need for mechanical ventilation, cardiomyopathy, retrognathism, and arthrogryposis. All our patients were stillborn or died within 1 month of life. In addition, we identified five novel GBE1 variants.

Stochastic modelling of a three-dimensional glycogen granule synthesis and impact of the branching enzyme

In humans, glycogen storage diseases result from metabolic inborn errors, and can lead to severe phenotypes and lethal conditions. Besides these rare diseases, glycogen is also associated to widely spread societal burdens such as diabetes. Glycogen is a branched glucose polymer synthesised and degraded by a complex set of enzymes. Over the past 50 years, the structure of glycogen has been intensively investigated. Yet, the interplay between the detailed three-dimensional glycogen structure and the related enzyme activity is only partially characterised and still to be fully understood. In this article, we develop a stochastic coarse-grained and spatially resolved model of branched polymer biosynthesis following a Gillespie algorithm. Our study largely focusses on the role of the branching enzyme, and first investigates the properties of the model with generic parameter values, before comparing it to in vivo experimental data in mice. It arises that the ratio of glycogen synthase over branching enzyme reaction rates drastically impacts the structure of the granule. We deeply investigate the mechanism of branching and parametrise it using distinct lengths. Not only do we consider various possible sets of values for these lengths, but also distinct rules to apply them. We show how combining various values for these lengths finely tunes glycogen macromolecular structure. Comparing the model with experimental data confirms that we can accurately reproduce glycogen chain length distributions in wild type mice. Additional granule properties obtained for this fit are also in good agreement with typically reported values in the experimental literature. Nonetheless, we find that the mechanism of branching must be more flexible than usually reported. Overall, our model provides a theoretical basis to quantify the effect that single enzymatic parameters, in particular of the branching enzyme, have on the chain length distribution. Our generic model and methods can be applied to any glycogen data set, and could in particular contribute to characterise the mechanisms responsible for glycogen storage disorders.

Molecular basis for the regulation of human glycogen synthase by phosphorylation and glucose-6-phosphate

Glycogen synthase (GYS1) is the central enzyme in muscle glycogen biosynthesis. GYS1 activity is inhibited by phosphorylation of its amino (N) and carboxyl (C) termini, which is relieved by allosteric activation of glucose-6-phosphate (Glc6P). We present cryo-EM structures at 3.0-4.0 Å resolution of phosphorylated human GYS1, in complex with a minimal interacting region of glycogenin, in the inhibited, activated and catalytically competent states. Phosphorylations of specific terminal residues are sensed by different arginine clusters, locking the GYS1 tetramer in an inhibited state via intersubunit interactions. The Glc6P activator promotes conformational change by disrupting these interactions and increases the flexibility of GYS1, such that it is poised to adopt a catalytically competent state when the sugar donor UDP-glucose (UDP-glc) binds. We also identify an inhibited-like conformation that has not transitioned into the activated state, in which the locking interaction of phosphorylation with the arginine cluster impedes subsequent conformational changes due to Glc6P binding. Our results address longstanding questions regarding the mechanism of human GYS1 regulation.

GBE1 Is an Independent Prognostic Marker and Associated With CD163+ Tumor-Associated Macrophage Infiltration in Lung Adenocarcinoma

Glycogen branching enzyme (GBE1) is a critical gene that participates in regulating glycogen metabolism. However, the correlations between GBE1 expression and the prognosis and tumor-associated macrophages in lung adenocarcinoma (LUAD) also remain unclear. Herein, we firstly analyzed the expression level of GBE1 in LUAD tissues and adjacent lung tissues via The Cancer Genome Atlas (TCGA) database. The effect of GBE1 on prognosis was estimated by utilizing TCGA database and the PrognoScan database. The relationships between the clinical characteristics and GBE1 expression were evaluated via TCGA database. We then investigated the relationships between GBE1 and infiltration of immune cells in LUAD by utilizing the CIBERSORT algorithm and Tumor Immune Estimation Resource (TIMER) database. In addition, we used a tissue microarray (TMA) containing 92 LUAD tissues and 88 adjacent lung tissues with immunohistochemistry staining to verify the association between GBE1 expression and clinical characteristics, as well as the immune cell infiltrations. We found the expression level of GBE1 was significantly higher in LUAD tissues. High expression of GBE1 was associated with poorer overall survival (OS) in LUAD. In addition, high expression of GBE1 was correlated with advanced T classification, N classification, M classification, TNM stage, and lower grade. Moreover, GBE1 was positively correlated with infiltrating levels of CD163⁺ tumor-associated macrophages in LUAD. In conclusion, the expression of GBE1 is associated with the prognosis and CD163⁺ tumor-associated macrophage infiltration in LUAD, suggesting that it has potential to be prognostic and immunological biomarkers in LUAD.

Whole Transcriptome Analysis Reveals a Potential Regulatory Mechanism of LncRNA-FNIP2/miR-24-3p/FNIP2 Axis in Chicken Adipogenesis

Lipid biosynthesis is a complex process, which is regulated by multiple factors including lncRNA. However, the role of lncRNA in chicken abdominal fat accumulation is still unclear. In this research, we collected liver tissues from six high abdominal fat rate Sanhuang broilers and six low abdominal fat rate Sanhuang broilers to perform lncRNA sequencing and small RNA sequencing. A total of 2,265 lncRNAs, 245 miRNAs, and 5,315 mRNAs were differently expressed. Among of them, 1,136 differently expressed genes were enriched in the metabolic process. A total of 36 differently expressed genes, which were considered as differently expressed lncRNAs' targets, were enriched in the metabolic process. In addition, we also found out that eight differently expressed miRNAs could target 19 differently expressed genes. FNIP2 and PEX5L were shared in a cis-regulatory network and a differently expressed miRNA target relationship network. LncRNA-FNIP2/miR-24-3p/FNIP2 axis was considered as a potential candidate that may participate in lipid synthesis. Experimentally, the objective reality of lncRNA-FNIP2/miR-24-3p/FNIP2 axis was clarified and the regulation effect of lncRNA-FNIP2/miR-24-3p/FNIP2 axis on synthesis was validated. In brief, our study reveals a potential novel regulatory mechanism that lncRNA-FNIP2/miR-24-3p/FNIP2 axis was considered as being involved in lipid synthesis during chicken adipogenesis in liver.

Cellular Control of Viscosity Counters Changes in Temperature and Energy Availability

Cellular functioning requires the orchestration of thousands of molecular interactions in time and space. Yet most molecules in a cell move by diffusion, which is sensitive to external factors like temperature. How cells sustain complex, diffusion-based systems across wide temperature ranges is unknown. Here, we uncover a mechanism by which budding yeast modulate viscosity in response to temperature and energy availability. This "viscoadaptation" uses regulated synthesis of glycogen and trehalose to vary the viscosity of the cytosol. Viscoadaptation functions as a stress response and a homeostatic mechanism, allowing cells to maintain invariant diffusion across a 20°C temperature range. Perturbations to viscoadaptation affect solubility and phase separation, suggesting that viscoadaptation may have implications for multiple biophysical processes in the cell. Conditions that lower ATP trigger viscoadaptation, linking energy availability to rate regulation of diffusion-controlled processes. Viscoadaptation reveals viscosity to be a tunable property for regulating diffusion-controlled processes in a changing environment.

Hypoxia-induced GBE1 expression promotes tumor progression through metabolic reprogramming in lung adenocarcinoma

Hypoxia mediates a metabolic switch from oxidative phosphorylation to glycolysis and increases glycogen synthesis. We previously found that glycogen branching enzyme (GBE1) is downstream of the hypoxia-inducible factor-1 (HIF1) signaling pathway in lung adenocarcinoma (LUAD) cells; however, the molecular mechanism underlying HIF1 regulation of GBE1 expression remains unknown. Herein, the effect of GBE1 on tumor progression via changes in metabolic signaling under hypoxia in vitro and in vivo was evaluated, and GBE1-related genes from human specimens and data sets were analyzed. Hypoxia induced GBE1 upregulation in LUAD cells. GBE1-knockdown A549 cells showed impaired cell proliferation, clone formation, cell migration and invasion, angiogenesis, tumor growth, and metastasis. GBE1 mediated the metabolic reprogramming of LUAD cells. The expression of gluconeogenesis pathway molecules, especially fructose-1,6-bisphosphatase (FBP1), was markedly higher in shGBE1 A549 cells than it was in the control cells. FBP1 inhibited the tumor progression of LUAD. GBE1-mediated FBP1 suppression via promoter methylation enhanced HIF1α levels through NF-κB signaling. GBE1 may be a negative prognostic biomarker for LUAD patients. Altogether, hypoxia-induced HIF1α mediated GBE1 upregulation, suppressing FBP1 expression by promoter methylation via NF-κB signaling in LUAD cells. FBP1 blockade upregulated HIF1α, triggered the switch to anaerobic glycolysis, and enhanced glucose uptake. Therefore, targeting HIF1α/GBE1/NF-κB/FBP1 signaling may be a potential therapeutic strategy for LUAD.

Two cases of a non-progressive hepatic form of glycogen storage disease type IV with atypical liver pathology

Glycogen storage disease type IV (GSD IV) is a rare inborn metabolic disorder characterized by the accumulation of amylopectin-like glycogen in the liver or other organs. The hepatic subtype may appear normal at birth but rapidly develops to liver cirrhosis in infancy. Liver pathological findings help diagnose the hepatic form of the disease, supported by analyses of enzyme activity and GBE1 gene variants. Pathology usually shows periodic acid-Schiff (PAS) positive hepatocytes resistant to diastase. We report two cases of hepatic GSD IV with pathology showing PAS positive hepatocytes that were mostly digested by diastase, which differ from past cases. Gene analysis was critical for the diagnosis. Both cases were found to have the same variants c.288delA (p.Gly97GlufsTer46) and c.1825G > A (p.Glu609Lys). These findings suggest that c.1825G > A variant might be a common variant in the non-progressive hepatic form of GSD IV.

Glycogen storage disease type IV: dilated cardiomyopathy as the isolated initial presentation in an adult patient

Glycogen storage disease type IV (GSD IV, Andersen disease) is a rare autosomal recessive condition. The childhood neuromuscular subtype of GSD IV is characterised by a progressive skeletal myopathy with cardiomyopathy also reported in some individuals. We report a case of a 19-year-old man who presented with severe non-ischaemic dilated cardiomyopathy (NIDCM) necessitating heart transplantation, with biopsy showing aggregations of polyglucosan bodies in cardiac myocytes. He had no signs or symptoms of muscle weakness, liver dysfunction or neurologic involvement. A homozygous GBE1 c.607C>A (p.His203Asn) variant was identified. Our case is unusual in that our patient presented with an isolated NIDCM in the absence of other clinical manifestations of GSD IV. This case highlights the importance of considering storage disorders in young adults presenting with isolated NIDCM of unknown aetiology. It also emphasises the potential synergy between histopathological evaluation and genomic testing in enhancing diagnostic certainty.

Lung adenocarcinoma-intrinsic GBE1 signaling inhibits anti-tumor immunity

BACKGROUND

Changes in glycogen metabolism is an essential feature among the various metabolic adaptations used by cancer cells to adjust to the conditions imposed by the tumor microenvironment. Our previous study showed that glycogen branching enzyme (GBE1) is downstream of the HIF1 pathway in hypoxia-conditioned lung cancer cells. In the present study, we investigated whether GBE1 is involved in the immune regulation of the tumor microenvironment in lung adenocarcinoma (LUAD).

METHODS

We used RNA-sequencing analysis and the multiplex assay to determine changes in GBE1 knockdown cells. The role of GBE1 in LUAD was evaluated both in vitro and in vivo.

RESULTS

GBE1 knockdown increased the expression of chemokines CCL5 and CXCL10 in A549 cells. CD8 expression correlated positively with CCL5 and CXCL10 expression in LUAD. The supernatants from the GBE1 knockdown cells increased recruitment of CD8+ T lymphocytes. However, the neutralizing antibodies of CCL5 or CXCL10 significantly inhibited cell migration induced by shGBE1 cell supernatants. STING/IFN-I pathway mediated the effect of GBE1 knockdown for CCL5 and CXCL10 upregulation. Moreover, PD-L1 increased significantly in shGBE1 A549 cells compared to those in control cells. Additionally, in LUAD tumor tissues, a negative link between PD-L1 and GBE1 was observed. Lastly, blockade of GBE1 signaling combined with anti-PD-L1 antibody significantly inhibited tumor growth in vivo.

CONCLUSIONS

GBE1 blockade promotes the secretion of CCL5 and CXCL10 to recruit CD8+ T lymphocytes to the tumor microenvironment via the IFN-I/STING signaling pathway, accompanied by upregulation of PD-L1 in LUAD cells, suggesting that GBE1 could be a promising target for achieving tumor regression through cancer immunotherapy in LUAD.

Case of Neonatal Fatality from Neuromuscular Variant of Glycogen Storage Disease Type IV

Glycogen storage disease type IV (GSD-IV), or Andersen disease, is a rare autosomal recessive disorder that results from the deficiency of glycogen branching enzyme (GBE). This in turn results in accumulation of abnormal glycogen molecules that have longer outer chains and fewer branch points. GSD-IV manifests in a wide spectrum, with variable phenotypes depending on the degree and type of tissues in which this abnormal glycogen accumulates. Typically, GSD-IV presents with rapidly progressive liver cirrhosis and death in early childhood. However, there is a severe congenital neuromuscular variant of GSD-IV that has been reported in the literature, with fewer than 20 patient cases thus far. We report an unusual case of GSD-IV neuromuscular variant in a late preterm female infant who was born to non-consanguineous healthy parents with previously healthy children. Prenatally, our patient was found to have decreased fetal movement and polyhydramnios warranting an early delivery. Postnatally, she had severe hypotonia and respiratory failure, with no hepatic or cardiac involvement. Extensive metabolic and neurological workup revealed no abnormalities. However, molecular analysis by whole-exome sequencing revealed two pathogenic variants in the GBE1 gene. Our patient was thus a compound heterozygote of the two pathogenic variants: one of these was inherited from the mother [p.L490WfsX5 (c.1468delC)], and the other pathogenic variant was a de novo change [p.E449X (c.1245G>T)]. As expected in GSD-IV, diffuse intracytoplasmic periodic acid-Schiff-positive, diastase-resistant inclusions were found in the cardiac myocytes, hepatocytes, and skeletal muscle fibers of our patient.

A Case of Glycogen Storage Disease IV with Rare Homozygous Mutations in the Glycogen Branching Enzyme Gene

Glycogen storage disease (GSD) IV is a rare autosomal recessive inherited disorder caused by mutations in the gene coding for glycogen branching enzyme leading to progressive liver disease. GSD IV is associated with mutations in GBE1, which encodes the glycogen branching enzyme. We report a case of GSD IV with rare homozygous mutations in the GBE1 gene (c.791G>A (p.Gly264Glu), which was successfully treated by liver transplantation.

Analysis of GBE1 mutations via protein expression studies in glycogen storage disease type IV: A report on a non-progressive form with a literature review

Background

Glycogen storage disease type IV (GSD IV), caused by GBE1 mutations, has a quite wide phenotypic variation. While the classic hepatic form and the perinatal/neonatal neuromuscular forms result in early mortality, milder manifestations include non-progressive form (NP-GSD IV) and adult polyglucosan body disease (APBD). Thus far, only one clinical case of a patient with compound heterozygous mutations has been reported for the molecular analysis of NP-GSD IV. This study aimed to elucidate the molecular basis in a NP-GSD IV patient via protein expression analysis and to obtain a clearer genotype-phenotype relationship in GSD IV.

Case presentation

A Japanese boy presented hepatosplenomegaly at 2 years of age. Developmental delay, neurological symptoms, and cardiac dysfunction were not apparent. Observation of hepatocytes with periodic acid-Schiff-positive materials resistant to diastase, coupled with resolution of hepatosplenomegaly at 8 years of age, yielded a diagnosis of NP-GSD IV. Glycogen branching enzyme activity was decreased in erythrocytes. At 13 years of age, he developed epilepsy, which was successfully controlled by carbamazepine.

Molecular analysis

In this study, we identified compound heterozygous GBE1 mutations (p.Gln46Pro and p.Glu609Lys). The branching activities of the mutant proteins expressed using E. coli were examined in a reaction with starch. The result showed that both mutants had approximately 50% activity of the wild type protein.

Conclusion

This is the second clinical report of a NP-GSD IV patient with a definite molecular elucidation. Based on the clinical and genotypic overlapping between NP-GSD IV and APBD, we suggest both are in a continuum.

The dynamic life of the glycogen granule

Glycogen, the primary storage form of glucose, is a rapid and accessible form of energy that can be supplied to tissues on demand. Each glycogen granule, or "glycosome," is considered an independent metabolic unit composed of a highly branched polysaccharide and various proteins involved in its metabolism. In this Minireview, we review the literature to follow the dynamic life of a glycogen granule in a multicompartmentalized system, i.e. the cell, and how and where glycogen granules appear and the factors governing its degradation. A better understanding of the importance of cellular compartmentalization as a regulator of glycogen metabolism is needed to unravel its role in brain energetics.

Glycogen metabolism has a key role in the cancer microenvironment and provides new targets for cancer therapy

Metabolic reprogramming is a hallmark of cancer cells and contributes to their adaption within the tumour microenvironment and resistance to anticancer therapies. Recently, glycogen metabolism has become a recognised feature of cancer cells since it is upregulated in many tumour types, suggesting that it is an important aspect of cancer cell pathophysiology. Here, we provide an overview of glycogen metabolism and its regulation, with a focus on its role in metabolic reprogramming of cancer cells under stress conditions such as hypoxia, glucose deprivation and anticancer treatment. The various methods to detect glycogen in tumours in vivo as well as pharmacological modulators of glycogen metabolism are also reviewed. Finally, we discuss the therapeutic value of targeting glycogen metabolism as a strategy for combinational approaches in cancer treatment.

Structural basis of glycogen branching enzyme deficiency and pharmacologic rescue by rational peptide design

Glycogen branching enzyme 1 (GBE1) plays an essential role in glycogen biosynthesis by generating α-1,6-glucosidic branches from α-1,4-linked glucose chains, to increase solubility of the glycogen polymer. Mutations in the GBE1 gene lead to the heterogeneous early-onset glycogen storage disorder type IV (GSDIV) or the late-onset adult polyglucosan body disease (APBD). To better understand this essential enzyme, we crystallized human GBE1 in the apo form, and in complex with a tetra- or hepta-saccharide. The GBE1 structure reveals a conserved amylase core that houses the active centre for the branching reaction and harbours almost all GSDIV and APBD mutations. A non-catalytic binding cleft, proximal to the site of the common APBD mutation p.Y329S, was found to bind the tetra- and hepta-saccharides and may represent a higher-affinity site employed to anchor the complex glycogen substrate for the branching reaction. Expression of recombinant GBE1-p.Y329S resulted in drastically reduced protein yield and solubility compared with wild type, suggesting this disease allele causes protein misfolding and may be amenable to small molecule stabilization. To explore this, we generated a structural model of GBE1-p.Y329S and designed peptides ab initio to stabilize the mutation. As proof-of-principle, we evaluated treatment of one tetra-peptide, Leu-Thr-Lys-Glu, in APBD patient cells. We demonstrate intracellular transport of this peptide, its binding and stabilization of GBE1-p.Y329S, and 2-fold increased mutant enzymatic activity compared with untreated patient cells. Together, our data provide the rationale and starting point for the screening of small molecule chaperones, which could become novel therapies for this disease.

Metabolic and mitochondrial myopathies

Metabolic and mitochondrial myopathies encompass a heterogeneous group of disorders that result in impaired energy production in skeletal muscle. Symptoms of premature muscle fatigue, sometimes leading to myalgia, rhabdomyolysis, and myoglobinuria, typically occur with exercise that would normally depend on the defective metabolic pathway. But in another group of these disorders, the dominant muscle symptom is weakness. This article reviews the clinical features, diagnosis, and management of these diseases with emphasis on the recent literature.

Association of the congenital neuromuscular form of glycogen storage disease type IV with a large deletion and recurrent frameshift mutation

Anderson disease, also known as glycogen storage disease type IV (MIM 232500), is a rare autosomal recessive disorder caused by a deficiency of glycogen branching enzyme. Glycogen storage disease type IV has a broad clinical spectrum ranging from a perinatal lethal form to a nonprogressive later-onset disease in adults. Here, we report 2 unrelated infants who were born small for their gestational age and who had profound hypotonia at birth and thus needed mechanical ventilation. Both of these patients shared the same frameshift mutation (c.288delA, pGly97GlufsX46) in the GBE1 gene. In addition, both of these patients were found to have 2 different large deletions in the GBE1 gene; exon 7 and exons 2 to 7, respectively, on the other alleles. This case report also highlights the need for a more comprehensive search for large deletion mutations associated with glycogen storage disease type IV, especially if routine GBE1 gene sequencing results are equivocal.

Glycogen storage disease type IV: novel mutations and molecular characterization of a heterogeneous disorder

Glycogen storage disease type IV (GSD IV; Andersen disease) is caused by a deficiency of glycogen branching enzyme (GBE), leading to excessive deposition of structurally abnormal, amylopectin-like glycogen in affected tissues. The accumulated glycogen lacks multiple branch points and thus has longer outer branches and poor solubility, causing irreversible tissue and organ damage. Although classic GSD IV presents with early onset of hepatosplenomegaly with progressive liver cirrhosis, GSD IV exhibits extensive clinical heterogeneity with respect to age at onset and variability in pattern and extent of organ and tissue involvement. With the advent of cloning and determination of the genomic structure of the human GBE gene (GBE1), molecular analysis and characterization of underlying disease-causing mutations is now possible. A variety of disease-causing mutations have been identified in the GBE1 gene in GSD IV patients, many of whom presented with diverse clinical phenotypes. Detailed biochemical and genetic analyses of three unrelated patients suspected to have GSD IV are presented here. Two novel missense mutations (p.Met495Thr and p.Pro552Leu) and a novel 1-bp deletion mutation (c.1999delA) were identified. A variety of mutations in GBE1 have been previously reported, including missense and nonsense mutations, nucleotide deletions and insertions, and donor and acceptor splice-site mutations. Mutation analysis is useful in confirming the diagnosis of GSD IV--especially when higher residual GBE enzyme activity levels are seen and enzyme analysis is not definitive--and allows for further determination of potential genotype/phenotype correlations in this disease.

[Glycogenosis type IV (Andersen disease). Clinical data, pathology, and genetics in a fatal perinatal case]

Here we report the case of a newborn with glycogenosis type IV (Andersen disease), who died shortly after birth. The diagnosis was established in the first instance by light microscopy and histochemistry, and subsequently ultrastructurally. DNA could be extracted from a fibroblast cell culture by sequencing the causative GBE1 gene (glycogen branching enzyme 1). Two compound heterozygous mutations in the gene were identified. The differential diagnosis should include Lafora disease as well as polyglucosan body disease. Since there is no effective therapy for glycogenosis type IV to date, prenatal diagnosis is mandatory.

AMP-activated protein kinase--a sensor of glycogen as well as AMP and ATP?

The classical role of the AMP-activated protein kinase (AMPK) is to act as a sensor of the immediate availability of cellular energy, by monitoring the concentrations of AMP and ATP. However, the beta subunits of AMPK contain a glycogen-binding domain, and in this review we develop the hypothesis that this is a regulatory domain that allows AMPK to act as a sensor of the status of cellular reserves of energy in the form of glycogen. We argue that the pool of AMPK that is bound to the glycogen particle is in an active state when glycogen particles are fully synthesized, causing phosphorylation of glycogen synthase at site 2 and providing a feedback inhibition of further extension of the outer chains of glycogen. However, when glycogen becomes depleted, the glycogen-bound pool of AMPK becomes inhibited due to binding to alpha1-->6-linked branch points exposed by the action of phosphorylase and/or debranching enzyme. This allows dephosphorylation of site 2 on glycogen synthase by the glycogen-bound form of protein phosphatase-1, promoting rapid resynthesis of glycogen and replenishment of glycogen stores. This is an extension of the classical role of AMPK as a 'guardian of cellular energy', in which it ensures that cellular energy reserves are adequate for medium-term requirements. The literature concerning AMPK, glycogen structure and glycogen-binding proteins that led us to this concept is reviewed.

Living Donor Liver Transplantation in a Korean Child with Glycogen Storage Disease Type IV and a GBE1 Mutation

Glycogen storage disease type IV (GSD-IV) is an autosomal recessive disease caused by a deficient glycogen branching enzyme (GBE), encoded by the GBE1 gene, resulting in the accumulation of abnormal glycogen deposits in the liver and other tissues. We treated a 20-month-old girl who presented with progressive liver cirrhosis and was diagnosed with GSD-IV, as confirmed by GBE1 gene mutation analysis, and underwent living related heterozygous donor liver transplantation. Direct sequencing of the GBE1 gene revealed that the patient was compound heterozygous for a known c.1571G>A (p.Gly264Glu) mutation a novel c.791G>A (Arg524Gln) mutation. This is the first report of a Korean patient with GSD-IV confirmed by mutation analysis, who was treated successfully by liver transplantation.

Multisystem involvement in a patient due to accumulation of amylopectin-like material with diminished branching enzyme activity

We report a 13-year-old boy with multisystem involvement secondary to accumulation of amylopectin-like material. He was born to consanguineous parents at full term without any complications and his maternal perinatal history was uneventful. His parents were cousins. He had normal growth and development except for his weight. His sister died from an unexplained cardiomyopathy at the age of 8 years. Our patient's initial symptom was severe heart failure. Since he also had a complaint of muscle weakness, electromyography was performed which showed muscle involvement. The diagnosis was suggested by tissue biopsy of skeletal muscle showing intracellular, basophilic, diastase-resistant, periodic acid-Schiff-positive inclusion bodies and was confirmed by the presence of a completed branching enzyme deficiency. Similar intracytoplasmic inclusion-like bodies were also found in liver biopsy, but very few in number compared with the skeletal muscle. The patient died from an intercurrent infection. Postmortem endomyocardial biopsy revealed the same intracytoplasmic inclusions as described above affecting almost all myocardial cells. Ultrastructural examination of liver biopsy was nondiagnostic; however, myocardium showed prominent, large, intracytoplasmic deposits. Glycogen branching enzyme gene sequence was normal, and thus classical branching enzyme deficiency was excluded. Our patient represents the first molecular study performed on a patient in whom there was multiple system involvement secondary to accumulation of amylopectin-like material. We suggest that this is an as yet undefined and different phenotype of glycogen storage disease associated with multisystemic involvement.

Null mutations and lethal congenital form of glycogen storage disease type IV

Glycogen branching enzyme deficiency (glycogen storage disease type IV, GSD-IV) is a rare autosomal recessive disorder of the glycogen synthesis with high mortality. Two female newborns showed severe hypotonia at birth and both died of cardiorespiratory failure, at 4 and 12 weeks, respectively. In both patients, muscle biopsies showed deposits of PAS-positive diastase-resistant material and biochemical analysis in cultured fibroblasts showed markedly reduced glycogen branching enzyme activity. Direct sequencing of GBE1 gene revealed that patient 1 was homozygous for a novel c.691+5 g>c in intron 5 (IVS5+5 g>c). RT-PCR analysis of GBE1 transcripts from fibroblasts cDNA showed that this mutation produce aberrant splicing. Patient 2 was homozygous for a novel c.1643G>A mutation leading to a stop at codon 548 in exon 13 (p.W548X). These data underscore that in GSD-IV a severe phenotype correlates with null mutations, and indicate that RNA analysis is necessary to characterize functional consequences of intronic mutations.

Glycogen storage disease: clinical, biochemical, and molecular heterogeneity

Glycogen storage diseases (GSDs) are characterized by abnormal inherited glycogen metabolism in the liver, muscle, and brain and divided into types 0 to X. GSD type I, glucose 6-phosphatase system, has types Ia, Ib, Ic, and Id, glucose 6-phosphatase, glucose 6-phosphate translocase, pyrophosphate translocase, and glucose translocase deficiencies, respectively. GSD type II is caused by defective lysosomal alpha-glucosidase (GAA), subdivided into 4 onset forms. GSD type III, amylo-1,6-glucosidase deficiency, is subdivided into 6 forms. GSD type IV, Andersen disease or amylopectinosis, is caused by deficiency of the glycogen-branching enzyme in numerous forms. GSD type V, McArdle disease or muscle phosphorylase deficiency, is divided into 2 forms. GSD type VI is characterized by liver phosphorylase deficiency. GSD type VII, phosphofructokinase deficiency, has 2 subtypes. GSD types VIa, VIII, IX, or X are supposedly caused by tissue-specific phosphorylase kinase deficiency. GSD type 0, glycogen synthase deficiency, is divided into 2 subtypes.

Heterologous expression and characterization of a novel branching enzyme from the thermoalkaliphilic anaerobic bacterium Anaerobranca gottschalkii

The gene encoding the branching enzyme (BE) from the thermoalkaliphilic, anaerobic bacterium Anaerobranca gottschalkii was fused with a twin arginine translocation protein secretory-pathway-dependent signal sequence from Escherichia coli and expressed in Staphylococcus carnosus. The secreted BE was purified using hydrophobic interaction and gel filtration chromatography. The monomeric enzyme (72 kDa) shows maximal activity at 50 degrees C and pH 7.0. With amylose the BE displays high transglycosylation and extremely low hydrolytic activity. The conversion of amylose and linear dextrins was analysed by applying high-performance anion exchange chromatography and quantitative size-exclusion chromatography. Amylose (10(4)-4 x 10(7) g/mol) was converted to a major extent to products displaying molecular masses of 10(4)-4 x 10(5) g/mol, indicating that the enzyme could be applicable for the production of starch or dextrins with narrow molecular mass distributions. The majority of the transferred oligosaccharides, determined after enzymatic hydrolysis of the newly synthesized alpha-1,6 linkages, ranged between 10(3) and 10(4) g/mol, which corresponds to a degree of polymerisation (DP) of 6-60. The minimal donor chain length is DP 16. Furthermore, the obtained results support the hypotheses of a random endocleavage mechanism of BE and the occurrence of interchain branching.

Fatal infantile neuromuscular presentation of glycogen storage disease type IV

Glycogen storage disease type IV or Andersen disease is an autosomal recessive disorder due to deficiency of glycogen branching enzyme. Typically, glycogen storage disease type IV presents with rapidly progressive liver cirrhosis and death in childhood. Variants include a cardiopathic form of childhood, a relatively benign myopathic form of young adults, and a late-onset neurodegenerative disorder (adult polyglucosan body disease). A severe neuromuscular variant resembling Werdnig-Hoffmann disease has also been described in two patients. The objective was to describe two additional infants with the neuromuscular variant and novel mutations in the GBE1 gene. Branching enzyme assay, Western blot, RT-PCR and sequencing were performed in muscle biopsies from both patients. The cDNA of patient 1 was subcloned and sequenced to define the mutations. Muscle biopsies showed accumulation of periodic acid Schiff-positive, diastase-resistant storage material in both patients and increased lysosomal enzyme activity in patient 1. Branching enzyme activity in muscle was negligible in both patients, and Western blot showed decreased branching enzyme protein. Patient 1 had two single base pair deletions, one in exon 10 (1238delT) and the other in exon 12 (1467delC), and each parent was heterozygous for one of the deletions. Patient 2 had a large homozygous deletion that spanned 627 bp and included exons 8-12. Patient 1, who died at 41 days, had neurophysiological and neuropathological features of Spinal Muscular Atrophy. Patient 2, who died at 5(1/2) weeks, had a predominantly myopathic process. The infantile neuromuscular form of glycogen storage disease type IV is considered extremely rare, but our encountering two patients in close succession suggests that the disease may be underdiagnosed.

Severe neonatal onset of glycogenosis type IV: clinical and laboratory findings leading to diagnosis in two siblings

Glycogenosis type IV is an autosomal recessive disease, exceptionally diagnosed at birth: only very few reports of the fatal perinatal neuromuscular form have been described. We report on two sibling male newborns who died at 10 and 4 weeks of age with clinical signs of a systemic storage disease. Prenatal history included polyhydramnios, reduced fetal movements and fetal hydrops, and Caesarean section was performed at 36 weeks of gestational age because of fetal distress. At birth, both babies showed severe hypotonia, hyporeflexia and no spontaneous breathing activity. They never showed active movements, sucking and swallowing and were respirator-dependent until death. A muscle biopsy revealed, in both patients, the presence of PAS-positive and partially diastase-resistant cytoplasmic inclusions containing granular and filamentous amylopectin-like material. This suggested that the stored material consisted of abnormal glycogen. At autopsy, ultrastructural examination of cardiac and skeletal muscle, liver, kidney and brain showed PAS-positive diastase-resistant eosinophilic cytoplasmic inclusions. Determination of branching enzyme activity, in cultured fibroblasts from the second patient, showed markedly reduced enzyme activity, confirming diagnosis of glycogenosis type IV. Our patients showed the full spectrum of both prenatal signs (hydrops, polyhydramnios) and postnatal signs (hypotonia, hyporeflexia, absence of active movements, cardiomegaly), which have been reported previously. They suffered from a very severe form of glycogenosis type IV with clinical and histological involvement of many tissues and organs. Diagnosis was accomplished on the second baby and required several biochemical and histological studies, in order to rule out both neuromuscular disorders and the most common storage diseases with neonatal onset. In our experience, the correct interpretation of the histological findings was essential in the search for the diagnosis.

Identification of a novel protein interacting with laforin, the EPM2a progressive myoclonus epilepsy gene product

We have identified an interacting partner protein (encoded by the human EPM2AIP1 gene (approved symbol)) for laforin, the product of the EPM2A gene, which is mutated in an autosomal recessive form of adolescent progressive myoclonus epilepsy. The EPM2AIP1 gene was identified in a screen for laforin-interacting proteins with a human brain cDNA library using the yeast two-hybrid system. The specificity of the interaction was confirmed by coimmunoprecipitation of in vivo-transfected protein and by using EPM2A deletion constructs. Subcellular colocalization of laforin and EPM2AIP1 protein was also demonstrated. The human EPM2AIP1 gene, corresponding to the KIAA0766 cDNA clone in the databases, was characterized and shown, like EPM2A, to be ubiquitously expressed. The gene, which comprises one large exon 1824 nucleotides in length and has alternative 3' untranslated regions, maps to human chromosome 3p22.1. The function is currently not known and extensive analyses do not reveal any homology to other proteins or any obvious structural motifs. Because genetic heterogeneity in Lafora disease has been described, mutational analysis of the EPM2AIP1 gene was performed on non-EPM2A patients, but no mutations were found. The identification of this first binding partner for laforin promises to be an important step toward unraveling the underlying pathogenesis of this severest form of teenage-onset epilepsy.

Structural features of the glycogen branching enzyme encoding genes from aspergilli

A maltose binding protein, p78, was purified to homogeneity from Aspergillus nidulans by a single column chromatography step on cross-linked amylose. The partial amino acid sequence was highly homologous to the glycogen branching enzymes (GBEs) of human and yeast, and p78 did show branching enzyme activity. The genomic gene and its cDNA encoding GBE (p78) were isolated from the A. nidulans genomic and cDNA libraries. Furthermore, a cDNA encoding A. oryzae GBE was entirely sequenced. A. nidulans GBE shared overall and significant amino acid sequence identity with GBEs from A. oryzae (83.9%), Saccharomyces cerevisiae (61.1%) and human (63.0%), and with starch branching enzymes from green plants (55-56%).

Functional genomics: lessons from yeast

Functional genomics represents a systematic approach to elucidating the function of the novel genes revealed by complete genome sequences. Such an approach should adopt a hierarchical strategy since this will both limit the number of experiments to be performed and permit a closer and closer approximation to the function of any individual gene to be achieved. Moreover, hierarchical analyses have, in their early stages, tremendous integrative power and functional genomics aims at a comprehensive and integrative view of the workings of living cells. The first draft of the human genome sequence has just been produced, and the complete genome sequences of a number of eukaryotic human pathogens (including the parasitic protozoa Plasmodium, Leishmania, and Trypanosoma) will soon be available. However, the most rapid progress in the elucidation of gene function will initially be made using model organisms. Yeast is an excellent eukaryotic model and at least 40% of single-gene determinants of human heritable diseases find homologues in yeast. We have adopted a systematic approach to the functional analysis of the Saccharomyces cerevisiae genome. A number of the approaches for the functional analysis of novel yeast genes are discussed. The different approaches are grouped into four domains: genome, transcriptome, proteome, and metabolome. The utility of genetic, biochemical, and physico-chemical methods for the analysis of these domains is discussed, and the importance of framing precise biological questions, when using these comprehensive analytical methods, is emphasized. Finally, the prospects for elucidating the function of protozoan genes by using the methods pioneered with yeast, and even exploiting Saccharomyces itself, as a surrogate, are explored.

Lafora's disease: towards a clinical, pathologic, and molecular synthesis

Lafora's disease is one of five inherited progressive myoclonus epilepsy syndromes. It is an autosomal-recessive disorder with onset in late childhood or adolescence. Characteristic seizures include myoclonic and occipital lobe seizures with visual hallucinations, scotomata, and photoconvulsions. The course of the disease consists of worsening seizures and an inexorable decline in mental and other neurologic functions that result in dementia and death within 10 years of onset. Pathology reveals pathognomonic polyglucosan inclusions that are not seen in any other progressive myoclonus epilepsy. Lafora's disease is one of several neurologic conditions associated with brain polyglucosan bodies. Why Lafora's polyglucosan bodies alone are associated with epilepsy is unknown and is discussed in this article. Up to 80% of patients with Lafora's disease have mutations in the EPM2A gene. Although common mutations are rare, simple genetic tests to identify most mutations have been established. At least one other still-unknown gene causes Lafora's disease. The EPM2A gene codes for the protein laforin, which localizes at the plasma membrane and the rough endoplasmic reticulum and functions as a dual-specificity phosphatase. Work toward establishing the connection between laforin and Lafora's disease polyglucosans is underway, as are attempts to replace it into the central nervous system of patients with Lafora's disease.

Update on genetic disorders affecting white matter

The classification of diseases affecting white matter has changed dramatically with the use of magnetic resonance imaging. Classical leukodystrophies, such as metachromatic leukodystrophy and Krabbe's disease, account for only a small number of inherited diseases that affect white matter. Magnetic resonance imaging has clarified genetic disorders that result in white matter changes or leukoencephalopathies. The term leukoencephalopathy is used to reflect the broader number of diseases that may cause as either primary or secondary changes in myelin development. This review attempts to categorize white matter disorders into classes such as lipid, myelin protein, organic acids, and defects in energy metabolism, in addition to other causes.

Glycogen storage myopathies

The glycogen storage myopathies are caused by enzyme defects in the glycogenolytic or in the glycolytic pathway affecting skeletal muscle alone or in conjunction with other tissues. The authors review recent findings in this area, including a new entity, aldolase deficiency, and the wealth of molecular genetic data that are rapidly accumulating. Despite this progress, genotype-phenotyp3 correlations are still murky in most glycogen storage myopathies.

The molecular diagnosis of metabolic myopathies

The metabolic myopathies are distinguished by extensive clinical and genetic heterogeneity within and between individual disorders. There are a number of explanations for the variability observed that go beyond single gene mutations or degrees of heteroplasmy in the case of mitochondrial DNA mutations. Some of the contributing factors include protein subunit interactions, tissue-specificity, modifying genetic factors, and environmental triggers. Advances in the molecular analysis of metabolic myopathies during the last decade have not only improved the diagnosis of individual disorders but also helped to characterize the contributing factors that make these disorders so complex.

A novel missense mutation in the glycogen branching enzyme gene in a child with myopathy and hepatopathy

We have identified a novel missense mutation in the gene for glycogen branching enzyme (GBE 1) in a 16-month-old infant with a combination of hepatic and muscular features, an atypical clinical presentation of glycogenosis type IV (GSD IV). The patient was heterozygous for a G-to-A substitution at codon 524 (R524Q), changing an encoded arginine (CGA) to glutamine (CAA), while the GBE1 gene on the other allele was not expressed. This case broadens the spectrum of mutations in patients with GSD IV and confirms the clinical and molecular heterogeneity of this disease.

The molecular background of glycogen metabolism disorders

The molecular pathology of classical glycogen storage disorders, glycogen synthase deficiency and Fanconi-Bickel syndrome is reviewed. The isolation of the respective cDNAs, the chromosomal localization of the genes and the elucidation of the genomic organization enabled mutation analysis in most disorders. The findings have shed light on the multi-protein structure of the glucose-6-phosphatase system, the phosphorylase kinase enzymatic complex and the molecular background of the differential tissue expression in debranching enzyme deficiency. The immediate practical benefit of these studies is our extending ability to predict the outcome of clinical variants and to offer genetic counseling to most families. The elucidation of the tertiary structure of these proteins and their structure-function relationship poses major challenges for the future.

Adult polyglucosan body disease in Ashkenazi Jewish patients carrying the Tyr329Ser mutation in the glycogen-branching enzyme gene

Adult polyglucosan body disease (APBD) is a late-onset, slowly progressive disorder of the nervous system caused by glycogen branching enzyme (GBE) deficiency in a subgroup of patients of Ashkenazi Jewish origin. Similar biochemical finding is shared by glycogen storage disease type IV (GSD IV) that, in contrast to APBD, is an early childhood disorder with primarily systemic manifestations. Recently, the GBE cDNA was cloned and several mutations were characterized in different clinical forms of GSD IV. To examine whether mutations in the GBE gene account for APBD, we studied 7 patients from five Jewish families of Ashkenazi ancestry. The diagnosis was based on the typical clinical and pathological findings, and supported by reduced GBE activity. We found that the clinical and biochemical APBD phenotype in all five families cosegregated with the Tyr329Ser mutation, not detected in 140 controls. As this mutation was previously identified in a nonprogressive form of GSD IV and was shown in expression studies to result in a significant residual GBE activity, present findings explain the late onset and slowly progressive course of APBD in our patients. We conclude that APBD represents an allelic variant of GSD IV, but the reason for the difference in primary tissue involvement must be established.

Glycogen storage diseases and the liver

Carbohydrate metabolism in the liver is responsible for plasma glucose homeostasis. Liver glycogen storage diseases are metabolic disorders which result in abnormal storage amounts and/or forms of glycogen, and often (but not always) have hepatomegaly and hypoglycaemia as presenting features. To understand the clinical complexity of the glycogen storage diseases, it is necessary to understand the properties and regulation of the proteins involved in glycogen metabolism. Advances in treatment have greatly improved metabolic control and hence the quality of life and survival. However, the lack of understanding of the molecular basis of some of the clinical features of glycogen storage diseases makes it difficult logically to devise optimal treatment regimens to prevent some of the long-term complications. Recently, molecular biology has greatly advanced our understanding of the proteins and genes involved in liver glycogen metabolism and has led to better and less invasive methods of diagnosis of these disorders.

Glycogenin-2, a novel self-glucosylating protein involved in liver glycogen biosynthesis

Glycogenin is a self-glucosylating protein involved in the initiation phase of glycogen biosynthesis. A single mammalian gene had been reported to account for glycogen biogenesis in liver and muscle, the two major repositories of glycogen. We describe the characterization of novel forms of glycogenin, designated glycogenin-2 (GN-2), encoded by a second gene that is expressed preferentially in certain tissues, including liver, heart, and pancreas. Cloning of cDNAs encoding glycogenin-2 indicated the existence of multiple species, including three liver forms (GN-2alpha, GN-2beta, and GN-2gamma) generated in part by alternative splicing. Overall, GN-2 has 40-45% identity to muscle glycogenin but is 72% identical over a 200-residue segment thought to contain the catalytic domain. GN-2 expressed in Escherichia coli or COS cells is active in self-glucosylation assays, and self-glucosylated GN-2 can be elongated by skeletal muscle glycogen synthase. Antibodies raised against GN-2 produced in E. coli recognized proteins of Mr approximately 66,000 present in extracts of rat liver and in cultured H4IIEC3 hepatoma cells. In H4IIEC3 cells, most of the GN-2 was present as a free protein but some was covalently associated with glycogen fractions and was only released by treatment with alpha-amylase. H4IIEC3 cells also expressed the muscle form of glycogenin (glycogenin-1), which was attached to a chromatographically separable glycogen fraction.

From gene to screen with yeast

With the complete sequence now available, the yeast genome project enters a post-sequencing phase that will concentrate on a comprehensive determination of gene function. Novel techniques have been developed to undertake genome-wide functional analysis at the levels of phenotype, transcript and protein. These include techniques for the efficient deletion of individual genes while tagging the deletants with specific oligonucleotide signatures, as well as strategies to quantify the physiological effects of such deletions by comparing growth rates and metabolite profiles under a range of conditions. Comprehensive approaches to the study of gene expression include hybridization array technology to identify and quantify transcripts, and the exploitation of mass spectometry to identify proteins resolved by two-dimensional gel electrophoresis. Yeast presents opportunities for the discovery of new human medicines both via the recognition of functional homologies between human and yeast genes and by the use of yeast to express human coding sequences specifying potential drug targets.

Evidence for essential arginine residues at the active sites of maize branching enzymes

Alignment of 23 branching enzyme (BE) amino acid sequences from various species showed conservation of two arginine residues. Phenylglyoxal (PGO) was used to investigate the involvement of arginine residues of maize BEI and BEII in catalysis. BE was significantly inactivated by PGO in triethanolamine buffer at pH 8.5. The inactivation followed a time- and concentration-dependent manner and showed pseudo first-order kinetics. Slopes of 0.73 (BEI) and 1.05 (BEII) were obtained from double log plots of the observed rates of inactivation against the concentrations of PGO, suggesting that loss of BE activity results from as few as one arginine residue modified by PGO. BE inactivation was positively correlated with [14C]PGO incorporation into BE protein and was considerably protected by amylose and/or amylopectin, suggesting that the modified arginine residue may be involved in substrate binding or located near the substrate-binding sites of maize branching enzymes I and II.

Accurate mapping of the "acid meat" RN gene on genetic and physical maps of pig chromosome 15

It has been shown that a major gene, called RN, is responsible for the RTN technological yield, a meat quality porcine trait. Experimental families informative for the segregation of RN gene were constituted from animals belonging to the Laconie composite line. We have previously mapped the RN gene to Chromosome (Chr) 15 (Milan et al. Genet. Sel. Evol. 27, 195-199, 1995). A Chr 15 map was established with 16 markers. The RN gene was found to be located between markers Sw120 and Sw936, at 2 cM from Sw936 (LOD = 38.1). In addition, by localizing Sw936 at 15q21-22 using DISC-PCR, we also located RN on the physical map.