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  1. Article: CBS domains: structure, function, and pathology in human proteins.

    Ignoul, Sofie / Eggermont, Jan

    American journal of physiology. Cell physiology

    2005  Volume 289, Issue 6, Page(s) C1369–78

    Abstract: The cystathionine-beta-synthase (CBS) domain is an evolutionarily conserved protein domain that is present in the proteome of archaebacteria, prokaryotes, and eukaryotes. CBS domains usually come in tandem repeats and are found in cytosolic and membrane ... ...

    Abstract The cystathionine-beta-synthase (CBS) domain is an evolutionarily conserved protein domain that is present in the proteome of archaebacteria, prokaryotes, and eukaryotes. CBS domains usually come in tandem repeats and are found in cytosolic and membrane proteins performing different functions (metabolic enzymes, kinases, and channels). Crystallographic studies of bacterial CBS domains have shown that two CBS domains form an intramolecular dimeric structure (CBS pair). Several human hereditary diseases (homocystinuria, retinitis pigmentosa, hypertrophic cardiomyopathy, myotonia congenital, etc.) can be caused by mutations in CBS domains of, respectively, cystathionine-beta-synthase, inosine 5'-monophosphate dehydrogenase, AMP kinase, and chloride channels. Despite their clinical relevance, it remains to be established what the precise function of CBS domains is and how they affect the structural and/or functional properties of an enzyme, kinase, or channel. Depending on the protein in which they occur, CBS domains have been proposed to affect multimerization and sorting of proteins, channel gating, and ligand binding. However, recent experiments revealing that CBS domains can bind adenosine-containing ligands such ATP, AMP, or S-adenosylmethionine have led to the hypothesis that CBS domains function as sensors of intracellular metabolites.
    MeSH term(s) AMP-Activated Protein Kinases ; Animals ; Chloride Channels/genetics ; Chloride Channels/metabolism ; Cystathionine beta-Synthase/chemistry ; Cystathionine beta-Synthase/genetics ; Cystathionine beta-Synthase/metabolism ; Dimerization ; Genetic Diseases, Inborn/genetics ; Humans ; IMP Dehydrogenase/genetics ; IMP Dehydrogenase/metabolism ; Models, Molecular ; Multienzyme Complexes/genetics ; Multienzyme Complexes/metabolism ; Mutation ; Protein Structure, Tertiary ; Protein-Serine-Threonine Kinases/genetics ; Protein-Serine-Threonine Kinases/metabolism
    Chemical Substances Chloride Channels ; Multienzyme Complexes ; IMP Dehydrogenase (EC 1.1.1.205) ; Protein-Serine-Threonine Kinases (EC 2.7.11.1) ; AMP-Activated Protein Kinases (EC 2.7.11.31) ; Cystathionine beta-Synthase (EC 4.2.1.22)
    Language English
    Publishing date 2005-11-07
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Review
    ZDB-ID 392098-7
    ISSN 1522-1563 ; 0363-6143
    ISSN (online) 1522-1563
    ISSN 0363-6143
    DOI 10.1152/ajpcell.00282.2005
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Human ClC-6 is a late endosomal glycoprotein that associates with detergent-resistant lipid domains.

    Ignoul, Sofie / Simaels, Jeannine / Hermans, Diane / Annaert, Wim / Eggermont, Jan

    PloS one

    2007  Volume 2, Issue 5, Page(s) e474

    Abstract: Background: The mammalian CLC protein family comprises nine members (ClC-1 to -7 and ClC-Ka, -Kb) that function either as plasma membrane chloride channels or as intracellular chloride/proton antiporters, and that sustain a broad spectrum of cellular ... ...

    Abstract Background: The mammalian CLC protein family comprises nine members (ClC-1 to -7 and ClC-Ka, -Kb) that function either as plasma membrane chloride channels or as intracellular chloride/proton antiporters, and that sustain a broad spectrum of cellular processes, such as membrane excitability, transepithelial transport, endocytosis and lysosomal degradation. In this study we focus on human ClC-6, which is structurally most related to the late endosomal/lysomal ClC-7.
    Principal findings: Using a polyclonal affinity-purified antibody directed against a unique epitope in the ClC-6 COOH-terminal tail, we show that human ClC-6, when transfected in COS-1 cells, is N-glycosylated in a region that is evolutionary poorly conserved between mammalian CLC proteins and that is located between the predicted helices K and M. Three asparagine residues (N410, N422 and N432) have been defined by mutagenesis as acceptor sites for N-glycosylation, but only two of the three sites seem to be simultaneously N-glycosylated. In a differentiated human neuroblastoma cell line (SH-SY5Y), endogenous ClC-6 colocalizes with LAMP-1, a late endosomal/lysosomal marker, but not with early/recycling endosomal markers such as EEA-1 and transferrin receptor. In contrast, when transiently expressed in COS-1 or HeLa cells, human ClC-6 mainly overlaps with markers for early/recycling endosomes (transferrin receptor, EEA-1, Rab5, Rab4) and not with late endosomal/lysosomal markers (LAMP-1, Rab7). Analogously, overexpression of human ClC-6 in SH-SY5Y cells also leads to an early/recycling endosomal localization of the exogenously expressed ClC-6 protein. Finally, in transiently transfected COS-1 cells, ClC-6 copurifies with detergent-resistant membrane fractions, suggesting its partitioning in lipid rafts. Mutating a juxtamembrane string of basic amino acids (amino acids 71-75: KKGRR) disturbs the association with detergent-resistant membrane fractions and also affects the segregation of ClC-6 and ClC-7 when cotransfected in COS-1 cells.
    Conclusions: We conclude that human ClC-6 is an endosomal glycoprotein that partitions in detergent resistant lipid domains. The differential sorting of endogenous (late endosomal) versus overexpressed (early and recycling endosomal) ClC-6 is reminiscent of that of other late endosomal/lysosomal membrane proteins (e.g. LIMP II), and is consistent with a rate-limiting sorting step for ClC-6 between early endosomes and its final destination in late endosomes.
    MeSH term(s) Amino Acid Sequence ; Animals ; Antibodies/chemistry ; Antibodies/immunology ; Blotting, Western ; COS Cells ; Cell Line, Tumor ; Cercopithecus aethiops ; Chloride Channels/immunology ; Chloride Channels/metabolism ; Electrophoresis, Polyacrylamide Gel ; Glycosylation ; Humans ; Immunohistochemistry ; Lipid Metabolism ; Molecular Sequence Data ; Sequence Homology, Amino Acid
    Chemical Substances Antibodies ; CLCN6 protein, human ; Chloride Channels
    Language English
    Publishing date 2007-05-30
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ISSN 1932-6203
    ISSN (online) 1932-6203
    DOI 10.1371/journal.pone.0000474
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Human ClC-6 is a late endosomal glycoprotein that associates with detergent-resistant lipid domains.

    Sofie Ignoul / Jeannine Simaels / Diane Hermans / Wim Annaert / Jan Eggermont

    PLoS ONE, Vol 2, Iss 5, p e

    2007  Volume 474

    Abstract: BACKGROUND: The mammalian CLC protein family comprises nine members (ClC-1 to -7 and ClC-Ka, -Kb) that function either as plasma membrane chloride channels or as intracellular chloride/proton antiporters, and that sustain a broad spectrum of cellular ... ...

    Abstract BACKGROUND: The mammalian CLC protein family comprises nine members (ClC-1 to -7 and ClC-Ka, -Kb) that function either as plasma membrane chloride channels or as intracellular chloride/proton antiporters, and that sustain a broad spectrum of cellular processes, such as membrane excitability, transepithelial transport, endocytosis and lysosomal degradation. In this study we focus on human ClC-6, which is structurally most related to the late endosomal/lysomal ClC-7. PRINCIPAL FINDINGS: Using a polyclonal affinity-purified antibody directed against a unique epitope in the ClC-6 COOH-terminal tail, we show that human ClC-6, when transfected in COS-1 cells, is N-glycosylated in a region that is evolutionary poorly conserved between mammalian CLC proteins and that is located between the predicted helices K and M. Three asparagine residues (N410, N422 and N432) have been defined by mutagenesis as acceptor sites for N-glycosylation, but only two of the three sites seem to be simultaneously N-glycosylated. In a differentiated human neuroblastoma cell line (SH-SY5Y), endogenous ClC-6 colocalizes with LAMP-1, a late endosomal/lysosomal marker, but not with early/recycling endosomal markers such as EEA-1 and transferrin receptor. In contrast, when transiently expressed in COS-1 or HeLa cells, human ClC-6 mainly overlaps with markers for early/recycling endosomes (transferrin receptor, EEA-1, Rab5, Rab4) and not with late endosomal/lysosomal markers (LAMP-1, Rab7). Analogously, overexpression of human ClC-6 in SH-SY5Y cells also leads to an early/recycling endosomal localization of the exogenously expressed ClC-6 protein. Finally, in transiently transfected COS-1 cells, ClC-6 copurifies with detergent-resistant membrane fractions, suggesting its partitioning in lipid rafts. Mutating a juxtamembrane string of basic amino acids (amino acids 71-75: KKGRR) disturbs the association with detergent-resistant membrane fractions and also affects the segregation of ClC-6 and ClC-7 when cotransfected in COS-1 cells. CONCLUSIONS: We conclude that human ClC-6 is an endosomal glycoprotein that partitions in detergent resistant lipid domains. The differential sorting of endogenous (late endosomal) versus overexpressed (early and recycling endosomal) ClC-6 is reminiscent of that of other late endosomal/lysosomal membrane proteins (e.g. LIMP II), and is consistent with a rate-limiting sorting step for ClC-6 between early endosomes and its final destination in late endosomes.
    Keywords Medicine ; R ; Science ; Q
    Subject code 572
    Language English
    Publishing date 2007-01-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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