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Shi XZ, Zhong X, Yu XQ. Drosophila melanogaster NPC2 proteins bind bacterial cell wall components and may function in immune signal pathways. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2012; 42:545-56. [PMID: 22580186 PMCID: PMC3358802 DOI: 10.1016/j.ibmb.2012.04.002] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 03/22/2012] [Accepted: 04/13/2012] [Indexed: 05/14/2023]
Abstract
ML (MD-2 (myeloid differentiation factor-2)-related Lipid-recognition) is a conserved domain identified in MD-2, MD-1, NPC2 (Niemann-Pick disease type C2), and mite major allergen protein from animals, plants, and fungi. Vertebrate members of the ML family proteins, such as NPC2 and MD-2, play important roles in lipid metabolism and immune signaling pathway. MD-2 is an essential co-receptor in the lipopolysaccharide (LPS)/Toll-like receptor 4 (TLR4) signaling pathway. Insects contain multiple ML genes, arbitrarily named md-2- or npc2-like genes. However, whether insect ML genes have functions similar to vertebrate md-2 is unknown. In Drosophila melanogaster, there are eight npc2 genes (npc2a-h), and they can be further divided into three subgroups based on the numbers of cysteine residues (6, 7 and 8 Cys) in the mature proteins. The purpose of this study is to investigate whether any Drosophila npc2 genes may have functions in immune signaling pathways. We chose npc2a, npc2e and npc2h genes representing the three subgroups for this study. We showed that recombinant NPC2a, NPC2e and NPC2h not only bound to LPS and lipid A, but also bound to peptidoglycan (PG) and lipoteichoic acid (LTA), a property that has not been reported previously for vertebrate NPC2 or MD-2. More importantly, we showed that over-expression of NPC2a and NPC2e activated diptericin promoter reporter in S2 cells stimulated by PG, suggesting that NPC2e and NPC2a may play a role in the immune deficiency (Imd) pathway. This is the first in vitro study about NPC2 proteins in innate immunity of D. melanogaster.
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Affiliation(s)
| | | | - Xiao-Qiang Yu
- Send correspondence to: Xiao-Qiang Yu, PhD, Division of Cell Biology and Biophysics, School of Biological Sciences, University of Missouri-Kansas City, 5007 Rockhill Road, Kansas City, MO 64110, Telephone: (816)-235-6379, Fax: (816)-235-1503,
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2
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Martin DR, Cox NR, Morrison NE, Kennamer DM, Peck SL, Dodson AN, Gentry AS, Griffin B, Rolsma MD, Baker HJ. Mutation of the GM2 activator protein in a feline model of GM2 gangliosidosis. Acta Neuropathol 2005; 110:443-50. [PMID: 16200419 DOI: 10.1007/s00401-005-1040-6] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2005] [Revised: 04/29/2005] [Accepted: 04/30/2005] [Indexed: 12/01/2022]
Abstract
The G(M2) activator protein is required for successful degradation of G(M2) ganglioside by the A isozyme of lysosomal beta-N-acetylhexosaminidase (EC 3.2.1.52). Deficiency of the G(M2) activator protein leads to a relentlessly progressive accumulation of G(M2) ganglioside in neuronal lysosomes and subsequent fatal deterioration of central nervous system function. G(M2) activator deficiency has been described in humans, dogs and mice. This manuscript reports the discovery and characterization of a feline model of G(M2) activator deficiency that exhibits many disease traits typical of the disorder in other species. Cats deficient in the G(M2) activator protein develop clinical signs at approximately 14 months of age, including motor incoordination and exaggerated startle response to sharp sounds. Affected cats exhibit central nervous system abnormalities such as swollen neurons, membranous cytoplasmic bodies, increased sialic acid content and elevated levels of G(M2) ganglioside. As is typical of G(M2) activator deficiency, hexosaminidase A activity in tissue homogenates appears normal when assayed with a commonly used synthetic substrate. When the G(M2) activator cDNA was sequenced from normal and affected cats, a deletion of 4 base pairs was identified as the causative mutation, resulting in alteration of 21 amino acids at the C terminus of the G(M2) activator protein.
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Affiliation(s)
- Douglas R Martin
- Scott-Ritchey Research Center, College of Veterinary Medicine, Auburn University, Auburn, AL 36849-5525, USA.
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Sandhoff K, Kolter T. Biosynthesis and degradation of mammalian glycosphingolipids. Philos Trans R Soc Lond B Biol Sci 2003; 358:847-61. [PMID: 12803917 PMCID: PMC1693173 DOI: 10.1098/rstb.2003.1265] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Glycolipids are a large and heterogeneous family of sphingolipids that form complex patterns on eukaryotic cell surfaces. This molecular diversity is generated by only a few enzymes and is a paradigm of naturally occurring combinatorial synthesis. We report on the biosynthetic principles leading to this large molecular diversity and focus on sialic acid-containing glycolipids of the ganglio-series. These glycolipids are particularly concentrated in the plasma membrane of neuronal cells. Their de novo synthesis starts with the formation of the membrane anchor, ceramide, at the endoplasmic reticulum (ER) and is continued by glycosyltransferases of the Golgi complex. Recent findings from genetically engineered mice are discussed. The constitutive degradation of glycosphingolipids (GSLs) occurs in the acidic compartments, the endosomes and the lysosomes. Here, water-soluble glycosidases sequentially cleave off the terminal carbohydrate residues from glycolipids. For glycolipid substrates with short oligosaccharide chains, the additional presence of membrane-active sphingolipid activator proteins (SAPs) is required. A considerable part of our current knowledge about glycolipid degradation is derived from a class of human diseases, the sphingolipidoses, which are caused by inherited defects within this pathway. A new post-translational modification is the attachment of glycolipids to proteins of the human skin.
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Affiliation(s)
- Konrad Sandhoff
- Kekulé-Institut für Organische Chemie und Biochemie der Universität, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany.
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Kolodny EH. Molecular genetics of the beta-hexosaminidase isoenzymes: an introduction. ADVANCES IN GENETICS 2002; 44:101-26. [PMID: 11596976 DOI: 10.1016/s0065-2660(01)44074-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Affiliation(s)
- E H Kolodny
- Department of Neurology, New York University School of Medicine, New York, USA
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Mahuran DJ. Biochemical consequences of mutations causing the GM2 gangliosidoses. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1455:105-38. [PMID: 10571007 DOI: 10.1016/s0925-4439(99)00074-5] [Citation(s) in RCA: 199] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The hydrolysis of GM2-ganglioside is unusual in its requirements for the correct synthesis, processing, and ultimate combination of three gene products. Whereas two of these proteins are the alpha- (HEXA gene) and beta- (HEXB) subunits of beta-hexosaminidase A, the third is a small glycolipid transport protein, the GM2 activator protein (GM2A), which acts as a substrate specific co-factor for the enzyme. A deficiency of any one of these proteins leads to storage of the ganglioside, primarily in the lysosomes of neuronal cells, and one of the three forms of GM2-gangliosidosis, Tay-Sachs disease, Sandhoff disease or the AB-variant form. Studies of the biochemical impact of naturally occurring mutations associated with the GM2 gangliosidoses on mRNA splicing and stability, and on the intracellular transport and stability of the affected protein have provided some general insights into these complex cellular mechanisms. However, such studies have revealed little in the way of structure-function information on the proteins. It appears that the detrimental effect of most mutations is not specifically on functional elements of the protein, but rather on the proteins' overall folding and/or intracellular transport. The few exceptions to this generalization are missense mutations at two codons in HEXA, causing the unique biochemical phenotype known as the B1-variant, and one codon in both the HEXB and GM2A genes. Biochemical characterization of these mutations has led to the localization of functional residues and/or domains within each of the encoded proteins.
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Affiliation(s)
- D J Mahuran
- Research Institute, The Hospital for Sick Children, Toronto, Ont, Canada.
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Chen B, Rigat B, Curry C, Mahuran DJ. Structure of the GM2A gene: identification of an exon 2 nonsense mutation and a naturally occurring transcript with an in-frame deletion of exon 2. Am J Hum Genet 1999; 65:77-87. [PMID: 10364519 PMCID: PMC1378077 DOI: 10.1086/302463] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Deficiency of the GM2 activator protein, encoded by GM2A, results in the rare AB-variant form of GM2 gangliosidosis. Four mutations have been identified, but the human gene structure has been only partially characterized. We report a new patient from a Laotian deme whose cells are deficient in both GM2-activator mRNA and protein. However, reverse transcription (RT)-PCR detected some normal-sized cDNA and a smaller cDNA species, which was not seen in the RT-PCR products from normal controls. Sequencing revealed that, although the patient's normal-sized cDNA contained a single nonsense mutation in exon 2, his smaller cDNA was the result of an in-frame deletion of exon 2. Long PCR was used to amplify introns 1 and 2 from patient and normal genomic DNA, and no differences in size, in 5' and 3' end sequences, or in restriction-mapping patterns were observed. From these data we developed a set of four PCR primers that can be used to identify GM2A mutations. We use this procedure to demonstrate that the patient is likely homozygous for the nonsense mutation. Other reports have associated nonsense mutations with dramatically reduced levels of mRNA and with an increased level of skipping of the exon containing the mutation, thus reestablishing an open reading frame. However, a recent article has concluded that, in some cases, the latter observation is caused by an artifact of RT-PCR. In support of this conclusion, we demonstrate that, if the competing, normal-sized cDNA is removed from the initial RT-PCR products, from both patient and normal cells, by an exon 2-specific restriction digest; a second round of PCR produces similar amounts of exon 2-deleted cDNA.
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Affiliation(s)
- B Chen
- Research Institute, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
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Mahuran DJ. The GM2 activator protein, its roles as a co-factor in GM2 hydrolysis and as a general glycolipid transport protein. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1393:1-18. [PMID: 9714704 DOI: 10.1016/s0005-2760(98)00057-5] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Although there is only one documented function carried out by the GM2 activator protein in the lysosome, new information suggests that other less obvious roles may also be played by this protein in vivo. This information includes data demonstrating that the GM2 activator is a secretory, as well as a lysosomal protein, and that cells possess a carbohydrate-independent mechanism to re-capture the activator, with or without bound lipid, from the extracellular fluid. Additionally the GM2 activator has been shown to bind, solubilize and transport a broad spectrum of lipid molecules, such as glycolipids, gangliosides and at least one phosphoacylglycerol, between liposomes. At pH 7 the GM2 activator's rate of lipid transport is reduced by only 50% from its maximum rate which is achieved at approx. pH 5, suggesting that the GM2 activator may serve as a general intra- and/or inter-cellular lipid transport protein in vivo. Since the late 1970s the lysosomal form of the GM2 activator has been known to act as a substrate-specific co-factor for the hydrolysis of GM2 ganglioside by beta-hexosaminidase A. Gangliosides are a class of negatively charged glycolipids particularly abundant in neuronal cells which have been linked to numerous in vivo functions, such as memory formation and signal transduction events. Deficiency of the GM2 activator protein results in the storage of GM2 ganglioside and severe neurological disease, the AB-variant form of GM2 gangliosidosis, usually culminating in death before the age of 4 years. The exact mode-of-action of the GM2 activator in its role as a co-factor, and its specificity for various glycolipids are currently matters of debate in the literature.
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Affiliation(s)
- D J Mahuran
- Research Institute, The Hospital for Sick Children, 555 University Ave, Toronto, Ont. M5G 1X8, Canada.
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Smiljanic-Georgijev N, Rigat B, Xie B, Wang W, Mahuran DJ. Characterization of the affinity of the G(M2) activator protein for glycolipids by a fluorescence dequenching assay. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1339:192-202. [PMID: 9187239 DOI: 10.1016/s0167-4838(97)00002-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The G(M2) activator protein is a substrate specific cofactor for degradation of G(M2) ganglioside by lysosomal beta-hexosaminidase A. Mutations in the gene encoding the activator result in the AB-variant form of G(M2) gangliosidosis. The activator protein contains at least three functional elements; a hydrophobic binding pocket, an oligosaccharide binding site(s), and an area that interacts with hexosaminidase A. In this report a fluorescence dequenching assay specific for only the hydrophobic binding pocket is evaluated and optimized. It is shown that various glycolipids inhibit the transport between liposomes of a self-quenching fluorescent lipid probe, octadecylrhodamine, by the activator protein. The level of inhibition produced by each glycolipid is then used to characterize the oligosaccharide-binding specificity of the activator. The fluorescence dequenching assay is also used to evaluate the functionality of a truncated form of the activator protein. Our results indicate that this simple assay can be used to determine structure-function relationships within the normal or mutant forms of the activator. The data suggest that the C-terminus of the activator is required to produce a functional hydrophobic binding pocket.
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Affiliation(s)
- N Smiljanic-Georgijev
- Research Institute, The Hospital for Sick Children, University of Toronto, Ont., Canada
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Bertoni C, Appolloni MG, Stirling JL, Li SC, Li YT, Orlacchio A, Beccari T. Structural organization and expression of the gene for the mouse GM2 activator protein. Mamm Genome 1997; 8:90-3. [PMID: 27518306 DOI: 10.1007/s003359900364] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/1995] [Accepted: 10/13/1996] [Indexed: 10/18/2022]
Abstract
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.
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Affiliation(s)
- C Bertoni
- Dipartimento di Biologia Cellulare e Molecolare, Sezione di Biochimica e Biologia Molecolare, Università di Perugia, Via del Giochetto, 06126, Perugia, Italy
| | - M G Appolloni
- Dipartimento di Biologia Cellulare e Molecolare, Sezione di Biochimica e Biologia Molecolare, Università di Perugia, Via del Giochetto, 06126, Perugia, Italy
| | - J L Stirling
- Division of Life Sciences, King's College London, Campden Hill, W8 7AH, London, UK
| | - S C Li
- Department of Biochemistry, Tulane University Medical Center, 70112, New Orleans, Louisiana, USA
| | - Y T Li
- Department of Biochemistry, Tulane University Medical Center, 70112, New Orleans, Louisiana, USA
| | - A Orlacchio
- Dipartimento di Biologia Cellulare e Molecolare, Sezione di Biochimica e Biologia Molecolare, Università di Perugia, Via del Giochetto, 06126, Perugia, Italy
| | - T Beccari
- Dipartimento di Biologia Cellulare e Molecolare, Sezione di Biochimica e Biologia Molecolare, Università di Perugia, Via del Giochetto, 06126, Perugia, Italy
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Tassi C, Beccari T, Costanzi E, Orlacchio A. Beta-N-acetylhexosaminidase in spinal muscular atrophy fibroblasts. Clin Chim Acta 1993; 221:203-8. [PMID: 8149638 DOI: 10.1016/0009-8981(93)90035-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- C Tassi
- Department of Experimental Medicine and Biochemical Sciences, University of Perugia, Italy
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Bellachioma G, Stirling JL, Orlacchio A, Beccari T. Cloning and sequence analysis of a cDNA clone coding for the mouse GM2 activator protein. Biochem J 1993; 294 ( Pt 1):227-30. [PMID: 7689829 PMCID: PMC1134589 DOI: 10.1042/bj2940227] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
A cDNA (1.1 kb) containing the complete coding sequence for the mouse GM2 activator protein was isolated from a mouse macrophage library using a cDNA for the human protein as a probe. There was a single ATG located 12 bp from the 5' end of the cDNA clone followed by an open reading frame of 579 bp. Northern blot analysis of mouse macrophage RNA showed that there was a single band with a mobility corresponding to a size of 2.3 kb. We deduce from this that the mouse mRNA, in common with the mRNA for the human GM2 activator protein, has a long 3' untranslated sequence of approx. 1.7 kb. Alignment of the mouse and human deduced amino acid sequences showed 68% identity overall and 75% identity for the sequence on the C-terminal side of the first 31 residues, which in the human GM2 activator protein contains the signal peptide. Hydropathicity plots showed great similarity between the mouse and human sequences even in regions of low sequence similarity. There is a single N-glycosylation site in the mouse GM2 activator protein sequence (Asn151-Phe-Thr) which differs in its location from the single site reported in the human GM2 activator protein sequence (Asn63-Val-Thr).
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Affiliation(s)
- G Bellachioma
- Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Universita di Perugia, Italy
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Swallow DM, Islam I, Fox MF, Povey S, Klima H, Schepers U, Sandhoff K. Regional localization of the gene coding for the GM2 activator protein (GM2A) to chromosome 5q32-33 and confirmation of the assignment of GM2AP to chromosome 3. Ann Hum Genet 1993; 57:187-93. [PMID: 8257088 DOI: 10.1111/j.1469-1809.1993.tb01594.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The gene coding for the GM2 activator protein (GM2A) was previously mapped by us to chromosome 5 by an ELISA-based technique. Here we confirm this assignment using a PCR analysis of somatic cell hybrids and describe a regional localization to chromosome 5q32-33 by in situ hybridization. We also confirm the assignment of a pseudogene GM2AP to chromosome 3.
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Affiliation(s)
- D M Swallow
- MRC Human Biochemical Genetics Unit, Galton Laboratory, University College London, UK
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