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William E Balch

Publications and source records attributed to William E Balch.

32 records · Page 2Linked to original sources
PubMed2004

COPII-dependent export of cystic fibrosis transmembrane conductance regulator from the ER uses a di-acidic exit code.

Cystic fibrosis (CF) is a childhood hereditary disease in which the most common mutant form of the CF transmembrane conductance regulator (CFTR) DeltaF508 fails to exit the endoplasmic reticulum (ER). Export of wild-type CFTR from the ER requires the coat complex II (COPII) machinery, as it is sensitive to Sar1 mutants that disrupt normal coat assembly and disassembly. In contrast, COPII is not used to deliver CFTR to ER-associated degradation. We find that exit of wild-type CFTR from the ER is blocked by mutation of a consensus di-acidic ER exit motif present in the first nucleotide binding domain. Mutation of the code disrupts interaction with the COPII coat selection complex Sec23/Sec24. We propose that the di-acidic exit code plays a key role in linking CFTR to the COPII coat machinery and is the primary defect responsible for CF in DeltaF508-expressing patients.

Animals↗
PubMed2004

Ca2+ binding protects against gelsolin amyloidosis.

Amyloid diseases occur when native or mutant polypeptides misfold and aggregate to form deposits in the extracellular space. There are at least 20 proteins associated with amyloid diseases, including the well-known amyloid-beta peptide that is the causative agent for Alzheimer's disease (AD). This review describes familial amyloidosis of Finnish type (FAF), an amyloid disease caused by mutations in plasma gelsolin, a secreted protein that contains multiple Ca2+-binding domains. The FAF mutations result in a loss of the Ca2+-binding site in domain 2 of plasma gelsolin. The resulting decreased stability gives rise to susceptibility to the protease furin in the Golgi. Furin cleavage generates a secreted fragment that undergoes a second proteolytic event in the extracellular matrix to produce a peptide that self-assembles into amyloid plaques. Thus, Ca2+ binding in native plasma gelsolin protects against amyloid disease.

Amyloidosis, Familial↗
PubMed2004

Mise en place-this bud's for the Golgi.

Selective cargo export from the endoplasmic reticulum is brought about by the budding of COPII vesicles. While the main structural components of the COPII coat have been identified and characterized, the regulatory event(s) promoting COPII vesicle biogenesis and cargo selection still remains largely unknown. New data by Glick and colleagues suggest that Sec12 and COPII function may be downstream of important early events coordinated by transitional ER (tER) exit sites.

Animals↗
PubMed2003

Gelsolin domain 2 Ca2+ affinity determines susceptibility to furin proteolysis and familial amyloidosis of finnish type.

Mutation of aspartic acid 187 to asparagine (D187N) or tyrosine (D187Y) in domain 2 of the actin-modulating protein gelsolin causes the neurodegenerative disease familial amyloidosis of Finnish type (FAF). These mutations render plasma gelsolin susceptible to aberrant proteolysis by furin in the trans-Golgi network, the initial proteolytic event in the formation of 71 and 53 residue fragments that assemble into amyloid fibrils. Ca(2+) binding stabilizes wild-type domain 2 gelsolin against denaturation and proteolysis, but the FAF variants are unable to bind and be stabilized by Ca(2+). Though the chain of events initiating FAF has been elucidated recently, uncertainty remains about the mechanistic details that allow the FAF variants to be processed. To test the hypothesis that impaired Ca(2+) binding in the D187 variants, but not other factors specific to residue 187, increases susceptibility to aberrant proteolysis and subsequent amyloidogenesis, we designed the gelsolin variant E209Q to remove a different Ca(2+) ligand from the same Ca(2+) site that is affected in the FAF variants. Here, we show that E209Q domain 2 does not bind Ca(2+) and is not stabilized against denaturation or furin proteolysis, analogous to the behavior exhibited by the FAF variants. Transfection of full-length E209Q into COS cells results in secretion of both the full-length and furin-processed fragments, as observed with D187N and D187Y. Mutation of the furin consensus sequence in D187N and E209Q gelsolin prevents cleavage during secretion, indicating that inhibition of proprotein convertases (furin) represents a viable therapeutic approach for the treatment of FAF. Mutations that diminish domain 2 Ca(2+) binding allow furin access to an otherwise protected cleavage site, initiating the proteolytic cascade that leads to gelsolin amyloidogenesis and FAF.

Amyloid Neuropathies, Familial↗
PubMed2003

Molecular evolution of the Rab-escort-protein/guanine-nucleotide-dissociation-inhibitor superfamily.

Prenylation of Rab GTPases regulating vesicle traffic by Rab geranylgeranyltransferase (RabGGTase) requires a complex formed by the association of newly synthesized Rab proteins with Rab-escort-protein (REP), the choroideremia-gene-product that is mutated in disease, leading to loss of vision. After delivery to the membrane by the REP-Rab complex, subsequent recycling to the cytosol requires the REP-related guanine-nucleotide-dissociation-inhibitor (GDI). Although REP and GDI share common Rab-binding properties, GDI cannot assist in Rab prenylation and REP cannot retrieve Rab proteins from the membranes. We have now isolated REP mutant proteins that are able to partially function as both REP and GDI. These results provide molecular insight into the functional and evolutionary organization of the REP/GDI superfamily.

Alkyl and Aryl Transferases↗
PubMed2003

Amyloid as a natural product.

Amyloid fibrils, such as those found in Alzheimer's and the gelsolin amyloid diseases, result from the misassembly of peptides produced by either normal or aberrant intracellular proteolytic processing. A paper in this issue by Marks and colleagues (Berson et al., 2003) demonstrates that intra-melanosome fibrils are formed through normal biological proteolytic processing of an integral membrane protein. The resulting peptide fragment assembles into fibrils promoting the formation of melanin pigment granules. These results, along with the observation that amyloid fibril formation by bacteria is highly orchestrated, suggest that fibril formation is an evolutionary conserved biological pathway used to generate natural product nanostructures.

Amyloid↗
PubMed2003

Pathological and functional amyloid formation orchestrated by the secretory pathway.

Amyloidogenesis has historically been associated with pathology in a class of neurodegenerative diseases known as amyloid diseases. Recent studies have shown that proteolysis by furin during secretion initiates both variant gelsolin amyloidogenesis, associated with the disease familial amyloidosis of Finnish type, and Pmel17 fiber formation, which is necessary for the functional biogenesis of melanosomes. Proteolysis combined with organelle-dependent environment changes orchestrate amyloidogenesis associated with both pathological processes and a functional pathway.

Amyloid↗
PubMed2003

Geranylgeranyl switching regulates GDI-Rab GTPase recycling.

Rab GTPases, key regulators of membrane targeting and fusion, require the covalent attachment of geranylgeranyl lipids to their C terminus for function. To elucidate the role of lipid in Rab recycling, we have determined the crystal structure of Rab guanine nucleotide dissociation inhibitor (alphaGDI) in complex with a geranylgeranyl (GG) ligand (H(2)N-Cys-(S-GG)-OMe). The lipid is bound beneath the Rab binding platform in a shallow hydrophobic groove. Mutation of the binding pocket in the brain-specific alphaGDI leads to mental retardation. Strikingly, lipid binding acts through a conserved allosteric switching mechanism to promote release of the GDI-Rab[GDP] complex from the membrane.

Diterpenes↗
PubMed2002

Rab-alphaGDI activity is regulated by a Hsp90 chaperone complex.

The Rab-specific alphaGDP-dissociation inhibitor (alphaGDI) regulates the recycling of Rab GTPases. We have now identified a novel alphaGDI complex from synaptic membranes that contains three chaperone components: Hsp90, Hsc70 and cysteine string protein (CSP). We find that the alphaGDI-chaperone complex is dissociated in response to Ca(2+)-induced neurotransmitter release, that chaperone complex dissociation is sensitive to the Hsp90 inhibitor geldanamycin (GA) and that GA inhibits the ability of alphaGDI to recycle Rab3A during neurotransmitter release. We propose that alphaGDI interacts with a specialized membrane-associated Rab recycling Hsp90 chaperone system on the vesicle membrane to coordinate the Ca(2+)-dependent events triggering Rab-GTP hydrolysis with retrieval of Rab-GDP to the cytosol.

Adenosine Triphosphate↗
PubMed2002

Chemical chaperones increase the cellular activity of N370S beta -glucosidase: a therapeutic strategy for Gaucher disease.

Gaucher disease is a lysosomal storage disorder caused by deficient lysosomal beta-glucosidase (beta-Glu) activity. A marked decrease in enzyme activity results in progressive accumulation of the substrate (glucosylceramide) in macrophages, leading to hepatosplenomegaly, anemia, skeletal lesions, and sometimes CNS involvement. Enzyme replacement therapy for Gaucher disease is costly and relatively ineffective for CNS involvement. Chemical chaperones have been shown to stabilize various proteins against misfolding, increasing proper trafficking from the endoplasmic reticulum. We report herein that the addition of subinhibitory concentrations (10 microM) of N-(n-nonyl)deoxynojirimycin (NN-DNJ) to a fibroblast culture medium for 9 days leads to a 2-fold increase in the activity of N370S beta-Glu, the most common mutation causing Gaucher disease. Moreover, the increased activity persists for at least 6 days after the withdrawal of the putative chaperone. The NN-DNJ chaperone also increases WT beta-Glu activity, but not that of L444P, a less prevalent Gaucher disease variant. Incubation of isolated soluble WT enzyme with NN-DNJ reveals that beta-Glu is stabilized against heat denaturation in a dose-dependent fashion. We propose that NN-DNJ chaperones beta-Glu folding at neutral pH, thus allowing the stabilized enzyme to transit from the endoplasmic reticulum to the Golgi, enabling proper trafficking to the lysosome. Clinical data suggest that a modest increase in beta-Glu activity may be sufficient to achieve a therapeutic effect.

1-Deoxynojirimycin↗
PubMed2002

The delta subunit of AP-3 is required for efficient transport of VSV-G from the trans-Golgi network to the cell surface.

Vesicular stomatitis virus glycoprotein (VSV-G) is a transmembrane protein that functions as the surface coat of enveloped viral particles. We report the surprising result that VSV-G uses the tyrosine-based di-acidic motif (-YTDIE-) found in its cytoplasmic tail to recruit adaptor protein complex 3 for export from the trans-Golgi network. The same sorting code is used to recruit coat complex II to direct efficient transport from the endoplasmic reticulum to the Golgi apparatus. These results demonstrate that a single sorting sequence can interact with sequential coat machineries to direct transport through the secretory pathway. We propose that use of this compact sorting domain reflects a need for both efficient endoplasmic reticulum export and concentration of VSV-G into specialized post-trans-Golgi network secretory-lysosome type transport containers to facilitate formation of viral coats at the cell surface.

Adaptor Protein Complex 3↗
PubMed2002

Protein engineering for crystallization of the GTPase Sar1 that regulates ER vesicle budding.

Sar1 is an important and unique GTPase that regulates vesicle budding from the ER membrane. An effort to crystallize full-length hamster Sar1 was unsuccessful owing to the aggregation of Sar1 in solution as indicated by dynamic light-scattering measurements. It was presumed that a patch of hydrophobic residues in the N-terminal region of Sar1 was responsible for the aggregation. To attempt to improve protein crystallizability, the N-terminal residues of Sar1 were progressively truncated and the solution behavior of the resulting Sar1 variants was monitored by dynamic light scattering. Truncation of the first nine residues from the N-terminus led to a Sar1 variant that is monodisperse in solution. This well behaved Sar1 variant yielded crystals in just a few days that were ultimately refined to diffraction quality.

Animals↗
PubMed2002

Non-conventional trafficking of the cystic fibrosis transmembrane conductance regulator through the early secretory pathway.

The mechanism(s) of cystic fibrosis transmembrane conductance regulator (CFTR) trafficking from the endoplasmic reticulum (ER) through the Golgi apparatus, the step impaired in individuals afflicted with the prevalent CFTR-DeltaF508 mutation leading to cystic fibrosis, is largely unknown. Recent morphological observations suggested that CFTR is largely absent from the Golgi in situ (Bannykh, S. I., Bannykh, G. I., Fish, K. N., Moyer, B. D., Riordan, J. R., and Balch, W. E. (2000) Traffic 1, 852-870), raising the possibility of a novel trafficking pathway through the early secretory pathway. We now report that export of CFTR from the ER is regulated by the conventional coat protein complex II (COPII) in all cell types tested. Remarkably, in a cell type-specific manner, processing of CFTR from the core-glycosylated (band B) ER form to the complex-glycosylated (band C) isoform followed a non-conventional pathway that was insensitive to dominant negative Arf1, Rab1a/Rab2 GTPases, or the SNAp REceptor (SNARE) component syntaxin 5, all of which block the conventional trafficking pathway from the ER to the Golgi. Moreover, CFTR transport through the non-conventional pathway was potently blocked by overexpression of the late endosomal target-SNARE syntaxin 13, suggesting that recycling through a late Golgi/endosomal system was a prerequisite for CFTR maturation. We conclude that CFTR transport in the early secretory pathway can involve a novel pathway between the ER and late Golgi/endosomal compartments that may influence developmental expression of CFTR on the cell surface in polarized epithelial cells.

ADP-Ribosylation Factor 1↗