1
|
Han L, Ding G, Liu Y, Huang J, Wu J. Characterization of Sphingomyelin Phosphodiesterase Expression in Bumblebee (Bombus lantschouensis). JOURNAL OF INSECT SCIENCE (ONLINE) 2018; 18:5144942. [PMID: 30371875 PMCID: PMC6202439 DOI: 10.1093/jisesa/iey106] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Indexed: 06/08/2023]
Abstract
Sphingomyelin phosphodiesterase (SMPD) is a hydrolase that plays a major role in metabolic reactions involving sphingomyelin. Here, we describe an analysis of the cDNA sequence and gene structure of SMPD in bumblebee (Bombus lantschouensis). The expression of SMPD in different tissues and at different developmental stages and reproductive statuses was examined by real-time polymerase chain reaction (PCR). The results showed that the SMPD cDNA has a length of 2000 bp and contains an open reading frame (ORF) of 1,801 nucleotides that encodes a polypeptide of 599 amino acids. The full-length SMPD gene is 4228 bp and contains eight exons and seven introns. A comparative analysis revealed that the SMPD gene sequence in B. lantschouensis shares high sequence identity with those in other Bombus species. The SMPD gene is expressed broadly in various tissues and presents higher transcript levels in the ovary, midgut, and epidermis and thoracic tissues. Among the different developmental stages, the highest expression of SMPD was detected at the Pw pupal stage (pupae with an unpigmented body cuticle and white eyes), and the expression of this gene decreased from the Pp (pupae with pink eyes) to the Pdd (dark-eye pupae with a dark-pigmented cuticle) stages. In addition, SMPD expression was significantly upregulated after female egg laying. In conclusion, our results show that the bumblebee SMPD gene might play a key role at the Pw developmental stage and in female oviposition.
Collapse
Affiliation(s)
- Lei Han
- Key Laboratory of Insect-Pollinator Biology of the Ministry of Agriculture, Institute of Apicultural Research, Chinese Academy of Agricultural Sciences, Xiangshan, Haidian District, Beijing, China
| | - Guiling Ding
- Key Laboratory of Insect-Pollinator Biology of the Ministry of Agriculture, Institute of Apicultural Research, Chinese Academy of Agricultural Sciences, Xiangshan, Haidian District, Beijing, China
| | - Yanjie Liu
- Key Laboratory of Insect-Pollinator Biology of the Ministry of Agriculture, Institute of Apicultural Research, Chinese Academy of Agricultural Sciences, Xiangshan, Haidian District, Beijing, China
| | - Jiaxing Huang
- Key Laboratory of Insect-Pollinator Biology of the Ministry of Agriculture, Institute of Apicultural Research, Chinese Academy of Agricultural Sciences, Xiangshan, Haidian District, Beijing, China
| | - Jie Wu
- Key Laboratory of Insect-Pollinator Biology of the Ministry of Agriculture, Institute of Apicultural Research, Chinese Academy of Agricultural Sciences, Xiangshan, Haidian District, Beijing, China
| |
Collapse
|
2
|
Huta BP, Mehlenbacher MR, Nie Y, Lai X, Zubieta C, Bou-Abdallah F, Doyle RP. The Lysosomal Protein Saposin B Binds Chloroquine. ChemMedChem 2015; 11:277-82. [PMID: 26616259 DOI: 10.1002/cmdc.201500494] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Indexed: 11/09/2022]
Abstract
Chloroquine (CQ) has been widely used in the treatment of malaria since the 1950s, though toxicity and resistance is increasingly limiting its use in the clinic. More recently, CQ is also becoming recognized as an important therapeutic compound for the treatment of autoimmune disorders and has shown activity as an anticancer agent. However, the full extent of CQ pharmacology in humans is still unclear. Herein, we demonstrate that the lysosomal protein saposin B (sapB), critical for select lipid degradation, binds CQ with implications for both CQ function and toxicity. Using isothermal titration calorimetry (ITC) and fluorescence quenching experiments, CQ was shown to bind to the dimeric form of sapB at both pH 5.5 and pH 7.4 with an average binding affinity of 2.3×10(4) m(-1). X-ray crystallography confirmed this, and the first complete crystal structure of sapB with a bound small molecule (CQ) is reported. The results suggest that sapB might play a role in mitigating CQ-based toxicity and that sapB might itself be overwhelmed by CQ causing impaired lipid degradation.
Collapse
Affiliation(s)
- Brian P Huta
- Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY, 13244, USA
| | - Matthew R Mehlenbacher
- Department of Chemistry, State University of New York at Potsdam, Potsdam, NY, 13676, USA
| | - Yan Nie
- Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY, 13244, USA
| | - Xuelei Lai
- European Synchrotron Radiation Facility, Grenoble, 38054, France
| | - Chloe Zubieta
- Laboratoire de Physiologie Cellulaire & Végétale, iRTSV, UMR 5168, CNRS/CEA/INRA/Univ. Grenoble Alpes, Grenoble, 38054, France.
| | - Fadi Bou-Abdallah
- Department of Chemistry, State University of New York at Potsdam, Potsdam, NY, 13676, USA.
| | - Robert P Doyle
- Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY, 13244, USA.
| |
Collapse
|
3
|
Abstract
Lysosomes are cellular stomachs. They degrade macromolecules and release their components as nutrients into the cytosol. Digestion of sphingolipids and other membrane lipids occurs at luminal intraendosomal vesicles and IMs (intraendosomal membranes). Sphingolipid and membrane digestion needs catabolic hydrolases with the help of lipid-binding proteins [SAPs (sphingolipid activator proteins)] and anionic lipids such as BMP [bis(monoacylglycero)phosphate]. Inherited defects of hydrolases or SAPs or uptake of cationic amphiphilic drugs cause lipid accumulation, eventually leading to death, especially in inherited sphingolipid storage diseases. IMs are formed during endocytosis and their lipid composition is adjusted for degradation. Their cholesterol content, which stabilizes membranes, decreases and the level of negatively charged BMP, which stimulates sphingolipid degradation, increases. At the level of late endosomes, cholesterol is transported out of the luminal vesicles preferentially by cholesterol-binding proteins, NPC (Niemann-Pick type C)-2 and NPC-1. Their defects lead to an endolysosomal accumulation of cholesterol and sphingolipids in Niemann-Pick type C disease. BMP and ceramide stimulate NPC-2-mediated cholesterol transfer, whereas sphingomyelin inhibits it. Anionic membrane lipids also activate sphingomyelin degradation by ASM (acid sphingomyelinase), facilitating cholesterol export by NPC-2. ASM is a non-specific phospholipase C and degrades more than 23 phospholipids. SAPs are membrane-perturbing proteins which solubilize lipids, facilitating glycolipid digestion by presenting them to soluble catabolic enzymes at acidic pH. High BMP and low cholesterol levels favour lipid extraction and membrane disintegration by saposin A and B. The simultaneous inherited defect of saposins A-D causes a severe membrane and sphingolipid storage disease, also disrupting the water permeability barrier of the skin.
Collapse
|
4
|
Meyer RC, Giddens MM, Coleman BM, Hall RA. The protective role of prosaposin and its receptors in the nervous system. Brain Res 2014; 1585:1-12. [PMID: 25130661 DOI: 10.1016/j.brainres.2014.08.022] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Revised: 07/18/2014] [Accepted: 08/10/2014] [Indexed: 12/12/2022]
Abstract
Prosaposin (also known as SGP-1) is an intriguing multifunctional protein that plays roles both intracellularly, as a regulator of lysosomal enzyme function, and extracellularly, as a secreted factor with neuroprotective and glioprotective effects. Following secretion, prosaposin can undergo endocytosis via an interaction with the low-density lipoprotein-related receptor 1 (LRP1). The ability of secreted prosaposin to promote protective effects in the nervous system is known to involve activation of G proteins, and the orphan G protein-coupled receptors GPR37 and GPR37L1 have recently been shown to mediate signaling induced by both prosaposin and a fragment of prosaposin known as prosaptide. In this review, we describe recent advances in our understanding of prosaposin, its receptors and their importance in the nervous system.
Collapse
Affiliation(s)
- Rebecca C Meyer
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, United States
| | - Michelle M Giddens
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, United States
| | - Brilee M Coleman
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, United States
| | - Randy A Hall
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322, United States.
| |
Collapse
|
5
|
Schulze H, Sandhoff K. Sphingolipids and lysosomal pathologies. Biochim Biophys Acta Mol Cell Biol Lipids 2013; 1841:799-810. [PMID: 24184515 DOI: 10.1016/j.bbalip.2013.10.015] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Revised: 10/16/2013] [Accepted: 10/19/2013] [Indexed: 01/12/2023]
Abstract
Endocytosed (glyco)sphingolipids are degraded, together with other membrane lipids in a stepwise fashion by endolysosomal enzymes with the help of small lipid binding proteins, the sphingolipid activator proteins (SAPs), at the surface of intraluminal lysosomal vesicles. Inherited defects in a sphingolipid-degrading enzyme or SAP cause the accumulation of the corresponding lipid substrates, including cytotoxic lysosphingolipids, such as galactosylsphingosine and glucosylsphingosine, and lead to a sphingolipidosis. Analysis of patients with prosaposin deficiency revealed the accumulation of intra-endolysosmal vesicles and membrane structures (IM). Feeding of prosaposin reverses the storage, suggesting inner membrane structures as platforms of sphingolipid degradation. Water soluble enzymes can hardly attack sphingolipids embedded in the membrane of inner endolysosomal vesicles. The degradation of sphingolipids with few sugar residues therefore requires the help of the SAPs, and is strongly stimulated by anionic membrane lipids. IMs are rich in anionic bis(monoacylglycero)phosphate (BMP). This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.
Collapse
Affiliation(s)
- Heike Schulze
- LIMES, Membrane Biology & Lipid Biochemistry Unit, c/o Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Gerhard-Domagk-Str. 1, D-53115 Bonn, Germany
| | - Konrad Sandhoff
- LIMES, Membrane Biology & Lipid Biochemistry Unit, c/o Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Gerhard-Domagk-Str. 1, D-53115 Bonn, Germany.
| |
Collapse
|
6
|
Sun Y, Zamzow M, Ran H, Zhang W, Quinn B, Barnes S, Witte DP, Setchell KDR, Williams MT, Vorhees CV, Grabowski GA. Tissue-specific effects of saposin A and saposin B on glycosphingolipid degradation in mutant mice. Hum Mol Genet 2013; 22:2435-50. [PMID: 23446636 DOI: 10.1093/hmg/ddt096] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Individual saposin A (A-/-) and saposin B (B-/-)-deficient mice show unique phenotypes caused by insufficient degradation of myelin-related glycosphingolipids (GSLs): galactosylceramide and galactosylsphingosine and sulfatide, respectively. To gain insight into the interrelated functions of saposins A and B, combined saposin AB-deficient mice (AB-/-) were created by knock-in point mutations into the saposins A and B domains on the prosaposin locus. Saposin A and B proteins were undetectable in AB-/- mice, whereas prosaposin, saposin C and saposin D were expressed near wild-type (WT) levels. AB-/- mice developed neuromotor deterioration at >61 days and exhibited abnormal locomotor activity and enhanced tremor. AB-/- mice (~96 days) lived longer than A-/- mice (~85 days), but shorter than B-/- mice (~644 days). Storage materials were observed in Schwann cells and neuronal processes by electron microscopy. Accumulation of p62 and increased levels of LC3-II were detected in the brainstem suggesting altered autophagy. GSL analyses by (liquid chromatography) LC/MS identified substantial increases in lactosylceramide in AB-/- mouse livers. Sulfatide accumulated, but galactosylceramide remained at WT levels, in the AB-/- mouse brains and kidneys. Brain galactosylsphingosine in AB-/- mice was ~68% of that in A-/- mice. These findings indicate that combined saposins A and B deficiencies attenuated GalCer-β-galactosylceramidase and GM1-β-galactosidase functions in the degradation of lactosylceramide preferentially in the liver. Blocking sulfatide degradation from the saposin B deficiency diminished galactosylceramide accumulation in the brain and kidney and galctosylsphingosine in the brain. These analyses of AB-/- mice continue to delineate the tissue differential interactions of saposins in GSL metabolism.
Collapse
Affiliation(s)
- Ying Sun
- The Division of Human Genetics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Abstract
Saposins or sphingolipid activator proteins (SAPs) are small, nonenzymatic glycoproteins that are ubiquitously present in lysosomes. SAPs comprise the five molecules saposins A-D and the GM2 activator protein. Saposins are essential for sphingolipid degradation and membrane digestion. On the one hand, they bind the respective hydrolases required to catabolize sphingolipid molecules; on the other hand, saposins can interact with intralysosomal membrane structures to render lipids accessible to their degrading enzymes. Thus, saposins bridge the physicochemical gap between lipid substrate and hydrophilic hydrolases. Accordingly, defects in saposin function can lead to lysosomal lipid accumulation. In addition to their specific functions in sphingolipid metabolism, saposins have membrane-perturbing properties. At the low pH of lysosomes, saposins get protonated and exhibit a high binding affinity for anionic phospholipids. Based on their universal principle to interact with membrane bilayers, we present the immunological functions of saposins with regard to lipid antigen presentation to CD1-restricted T cells, processing of apoptotic bodies for antigen delivery and cross-priming, as well as their potential antimicrobial impact.
Collapse
Affiliation(s)
- Alexandre Darmoise
- Program in Cellular and Molecular Medicine at Children's Hospital, Immune Disease Institute, Department of Pathology, Harvard Medical School, Boston, MA, USA
| | | | | |
Collapse
|
8
|
Sun Y, Ran H, Zamzow M, Kitatani K, Skelton MR, Williams MT, Vorhees CV, Witte DP, Hannun YA, Grabowski GA. Specific saposin C deficiency: CNS impairment and acid beta-glucosidase effects in the mouse. Hum Mol Genet 2009; 19:634-47. [PMID: 20015957 PMCID: PMC2807372 DOI: 10.1093/hmg/ddp531] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Saposins A, B, C and D are derived from a common precursor, prosaposin (psap). The few patients with saposin C deficiency develop a Gaucher disease-like central nervous system (CNS) phenotype attributed to diminished glucosylceramide (GC) cleavage activity by acid β-glucosidase (GCase). The in vivo effects of saposin C were examined by creating mice with selective absence of saposin C (C−/−) using a knock-in point mutation (cysteine-to-proline) in exon 11 of the psap gene. In C−/− mice, prosaposin and saposins A, B and D proteins were present at near wild-type levels, but the saposin C protein was absent. By 1 year, the C−/− mice exhibited weakness of the hind limbs and progressive ataxia. Decreased neuromotor activity and impaired hippocampal long-term potentiation were evident. Foamy storage cells were observed in dorsal root ganglion and there was progressive loss of cerebellar Purkinje cells and atrophy of cerebellar granule cells. Ultrastructural analyses revealed inclusions in axonal processes in the spinal cord, sciatic nerve and brain, but no excess of multivesicular bodies. Activated microglial cells and astrocytes were present in thalamus, brain stem, cerebellum and spinal cord, indicating regional pro-inflammatory responses. No storage cells were found in visceral organs of these mice. The absence of saposin C led to moderate increases in GC and lactosylceramide (LacCer) and their deacylated analogues. These results support the view that saposin C has multiple roles in glycosphingolipid (GSL) catabolism as well as a prominent function in CNS and axonal integrity independent of its role as an optimizer/stabilizer of GCase.
Collapse
Affiliation(s)
- Ying Sun
- Division of Human Genetics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
9
|
Kolter T, Sandhoff K. Lysosomal degradation of membrane lipids. FEBS Lett 2009; 584:1700-12. [PMID: 19836391 DOI: 10.1016/j.febslet.2009.10.021] [Citation(s) in RCA: 201] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Accepted: 10/09/2009] [Indexed: 01/05/2023]
Abstract
The constitutive degradation of membrane components takes place in the acidic compartments of a cell, the endosomes and lysosomes. Sites of lipid degradation are intralysosomal membranes that are formed in endosomes, where the lipid composition is adjusted for degradation. Cholesterol is sorted out of the inner membranes, their content in bis(monoacylglycero)phosphate increases, and, most likely, sphingomyelin is degraded to ceramide. Together with endosomal and lysosomal lipid-binding proteins, the Niemann-Pick disease, type C2-protein, the GM2-activator, and the saposins sap-A, -B, -C, and -D, a suitable membrane lipid composition is required for degradation of complex lipids by hydrolytic enzymes.
Collapse
Affiliation(s)
- Thomas Kolter
- LiMES - Life and Medical Sciences Institute, Membrane Biology and Lipid Biochemistry Unit, c/o Kekulé-Institut für Organische Chemie und Biochemie, University of Bonn, Bonn, Germany
| | | |
Collapse
|
10
|
Sun Y, Witte DP, Ran H, Zamzow M, Barnes S, Cheng H, Han X, Williams MT, Skelton MR, Vorhees CV, Grabowski GA. Neurological deficits and glycosphingolipid accumulation in saposin B deficient mice. Hum Mol Genet 2008; 17:2345-56. [PMID: 18480170 PMCID: PMC2465797 DOI: 10.1093/hmg/ddn135] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Saposin B derives from the multi-functional precursor, prosaposin, and functions as an activity enhancer for several glycosphingolipid (GSL) hydrolases. Mutations in saposin B present in humans with phenotypes resembling metachromatic leukodystrophy. To gain insight into saposin B's physiological functions, a specific deficiency was created in mice by a knock-in mutation of an essential cysteine in exon 7 of the prosaposin locus. No saposin B protein was detected in the homozygotes (B−/−) mice, whereas prosaposin, and saposins A, C and D were at normal levels. B−/− mice exhibited slowly progressive neuromotor deterioration and minor head tremor by 15 months. Excess hydroxy and non-hydroxy fatty acid sulfatide levels were present in brain and kidney. Alcian blue positive (sulfatide) storage cells were found in the brain, spinal cord and kidney. Ultrastructural analyses showed lamellar inclusion material in the kidney, sciatic nerve, brain and spinal cord tissues. Lactosylceramide (LacCer) and globotriaosylceramide (TriCer) were increased in various tissues of B−/− mice supporting the in vivo role of saposin B in the degradation of these lipids. CD68 positive microglial cells and activated GFAP positive astrocytes showed a proinflammatory response in the brains of B−/− mice. These findings delineate the roles of saposin B for the in vivo degradation of several GSLs and its primary function in maintenance of CNS function. B−/− provide a useful model for understanding the contributions of this saposin to GSL metabolism and homeostasis.
Collapse
Affiliation(s)
- Ying Sun
- Division of Human Genetics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229-3039, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
11
|
Kolter T, Sandhoff K. Sphingolipid metabolism diseases. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1758:2057-79. [PMID: 16854371 DOI: 10.1016/j.bbamem.2006.05.027] [Citation(s) in RCA: 261] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2005] [Revised: 04/26/2006] [Accepted: 05/23/2006] [Indexed: 10/24/2022]
Abstract
Human diseases caused by alterations in the metabolism of sphingolipids or glycosphingolipids are mainly disorders of the degradation of these compounds. The sphingolipidoses are a group of monogenic inherited diseases caused by defects in the system of lysosomal sphingolipid degradation, with subsequent accumulation of non-degradable storage material in one or more organs. Most sphingolipidoses are associated with high mortality. Both, the ratio of substrate influx into the lysosomes and the reduced degradative capacity can be addressed by therapeutic approaches. In addition to symptomatic treatments, the current strategies for restoration of the reduced substrate degradation within the lysosome are enzyme replacement therapy (ERT), cell-mediated therapy (CMT) including bone marrow transplantation (BMT) and cell-mediated "cross correction", gene therapy, and enzyme-enhancement therapy with chemical chaperones. The reduction of substrate influx into the lysosomes can be achieved by substrate reduction therapy. Patients suffering from the attenuated form (type 1) of Gaucher disease and from Fabry disease have been successfully treated with ERT.
Collapse
Affiliation(s)
- Thomas Kolter
- Kekulé-Institut für Organische Chemie und Biochemie der Universität, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany.
| | | |
Collapse
|
12
|
Ciaffoni F, Tatti M, Boe A, Salvioli R, Fluharty A, Sonnino S, Vaccaro AM. Saposin B binds and transfers phospholipids. J Lipid Res 2006; 47:1045-53. [PMID: 16461955 DOI: 10.1194/jlr.m500547-jlr200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Saposin B (Sap B) is a member of a family of four small glycoproteins, Sap A, B, C, and D. Like the other three saposins, Sap B plays a physiological role in the lysosomal degradation of sphingolipids (SLs). Although the interaction of Sap B with SLs has been investigated extensively, that with the main membrane lipid components, namely phospholipids and cholesterol (Chol), is scarcely known. Using large unilamellar vesicles (LUVs) as membrane models, we have now found that Sap B simultaneously extracts from the lipid surface neutral [phosphatidylcholine (PC)] and anionic [phosphatidylinositol (PI)] phospholipids, fewer SLs [ganglioside GM1 (GM1) or cerebroside sulfate (CS)], and no Chol. More PI than SL (GM1 or CS) was solubilized from LUVs containing equal amounts of PI and SLs. An increase in PI level had a poor effect on the Sap B-induced solubilization of GM1 or CS but strongly inhibited that of PC. Sap B was able not only to bind, but also to transfer phospholipids between lipid surfaces. Both the phospholipid binding and transfer activities were optimal at low pH values. These results represent the first biochemical analysis of the Sap B interaction with phospholipids. The capacity of Sap B to bind and transfer phospholipids occurs under conditions mimicking the interior of the late endosomal/lysosomal compartment and thus might have physiological relevance.
Collapse
Affiliation(s)
- Fiorella Ciaffoni
- Department of Hematology, Oncology, and Molecular Medicine, Istituto Superiore Sanita, Roma, Italy
| | | | | | | | | | | | | |
Collapse
|
13
|
Kolter T, Sandhoff K. Principles of lysosomal membrane digestion: stimulation of sphingolipid degradation by sphingolipid activator proteins and anionic lysosomal lipids. Annu Rev Cell Dev Biol 2006; 21:81-103. [PMID: 16212488 DOI: 10.1146/annurev.cellbio.21.122303.120013] [Citation(s) in RCA: 343] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Sphingolipids and glycosphingolipids are membrane components of eukaryotic cell surfaces. Their constitutive degradation takes place on the surface of intra-endosomal and intra-lysosomal membrane structures. During endocytosis, these intra-lysosomal membranes are formed and prepared for digestion by a lipid-sorting process during which their cholesterol content decreases and the concentration of the negatively charged bis(monoacylglycero)phosphate (BMP)--erroneously also called lysobisphosphatidic acid (LBPA)--increases. Glycosphingolipid degradation requires the presence of water-soluble acid exohydrolases, sphingolipid activator proteins, and anionic phospholipids like BMP. The lysosomal degradation of sphingolipids with short hydrophilic head groups requires the presence of sphingolipid activator proteins (SAPs). These are the saposins (Saps) and the GM2 activator protein. Sphingolipid activator proteins are membrane-perturbing and lipid-binding proteins with different specificities for the bound lipid and the activated enzyme-catalyzed reaction. Their inherited deficiency leads to sphingolipid- and membrane-storage diseases. Sphingolipid activator proteins not only facilitate glycolipid digestion but also act as glycolipid transfer proteins facilitating the association of lipid antigens with immunoreceptors of the CD1 family.
Collapse
Affiliation(s)
- Thomas Kolter
- Kekulé-Institut für Organische Chemie und Biochemie der Universität, 53121 Bonn, Germany.
| | | |
Collapse
|
14
|
Kolter T, Winau F, Schaible UE, Leippe M, Sandhoff K. Lipid-binding Proteins in Membrane Digestion, Antigen Presentation, and Antimicrobial Defense. J Biol Chem 2005; 280:41125-8. [PMID: 16230343 DOI: 10.1074/jbc.r500015200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Affiliation(s)
- Thomas Kolter
- Kekulé-Institut für Organische Chemie und Biochemie, D-53121 Bonn, Germany
| | | | | | | | | |
Collapse
|
15
|
Norris AJ, Whitelegge JP, Yaghoubian A, Alattia JR, Privé GG, Toyokuni T, Sun H, Brooks MN, Panza L, Matto P, Compostella F, Remmel N, Klingenstein R, Sandhoff K, Fluharty C, Fluharty A, Faull KF. A novel mass spectrometric assay for the cerebroside sulfate activator protein (saposin B) and arylsulfatase A. J Lipid Res 2005; 46:2254-64. [PMID: 16061947 DOI: 10.1194/jlr.m500188-jlr200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A mass spectrometric method is described for monitoring cerebrosides in the presence of excess concentrations of alkali metal salts. This method has been adapted for use in the assay of arylsulfatase A (ASA) and the cerebroside sulfate activator protein (CSAct or saposin B). Detection of the neutral glycosphingolipid cerebroside product was achieved via enhancement of ionization efficiency in the presence of lithium ions. Assay samples were extracted into the chloroform phase as for the existing assays, dried, and diluted in methanol-chloroform-containing lithium chloride. Samples were analyzed by electrospray ionization mass spectrometry with a triple quadrupole mass spectrometer in the multiple reaction monitoring tandem mass spectrometric mode. The assay has been used to demonstrate several previously unknown or ambiguous aspects of the coupled ASA/CSAct reaction, including an absolute in vitro preference for CSAct over the other saposins (A, C, and D) and a preference for the non-hydroxylated species of the sulfatide substrate over the corresponding hydroxylated species. The modified assay for the coupled ASA/CSAct reaction could find applicability in settings in which the assay could not be performed previously because of the need for radiolabeled substrate, which is now not required.
Collapse
Affiliation(s)
- Andrew J Norris
- Pasarow Mass Spectrometry Laboratory, Department of Psychiatry, and Neuropsychiatric Institute, University of California Los Angeles, Los Angeles, CA 90024, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Bistoni O, Emiliani C, Agea E, Russano AM, Mencarelli S, Orlacchio A, Spinozzi F. Biochemical and Immunological Characterization of Pollen-Derived β-Galactosidase Reveals a New Cross-Reactive Class of Allergens among Mediterranean Trees. Int Arch Allergy Immunol 2005; 136:123-33. [PMID: 15650309 DOI: 10.1159/000083319] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2004] [Accepted: 09/22/2004] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The most potent allergens in the Spermatophytae family exhibit significant homology with enzymes. Some of these are though to be involved in pectin metabolism, recognition of compatible stigma and delivery of sperm cells to the ovule. OBJECTIVE To test if glycohydrolase activities from some Mediterranean tree pollens could act as allergens in sensitized hosts. METHODS Freshly collected Cupressus and Olea pollens were investigated for their glycohydrolase activities by means of synthetic fluorogenic substrates and isoenzymes characterized by DEAE-cellulose ion-exchange chromatography. Binding of specific IgE was investigated by immunoblotting in 30 tree-sensitive subjects, as well as in 20 atopic non-tree-sensitive and 15 healthy controls. The enzymes were also adopted to stimulate proliferation of allergen-specific T cell clones. Finally, they were tested in vivo in a cutaneous immediate wheal and flare reaction. RESULTS beta-Galactosidase (beta-GAL) is present with different isoenzymatic patterns on both pollen extracts, could be recognized by circulating IgE, as well as immunoprecipitated by sera from allergic subjects. The enzyme could stimulate the proliferation of T cells from allergic subjects, and favor the emergence of CD4+ T cell clones with specific in vitro reactivity to beta-GAL. Finally, the enzyme induced in vivo a cutaneous wheal and flare reaction in clinically sensitive subjects. CONCLUSIONS Despite different isoenzymatic patterns, Olea-derived beta-GAL cross-reacted with that from cypress pollen, suggesting that these enzymatic glycoproteins may represent major native allergens among these Mediterranean trees.
Collapse
Affiliation(s)
- Onelia Bistoni
- Laboratory of Experimental Immunology and Allergy, Department of Clinical and Experimental Medicine, University of Perugia, Perugia, Italy
| | | | | | | | | | | | | |
Collapse
|
17
|
Wendeler M, Hoernschemeyer J, John M, Werth N, Schoeniger M, Lemm T, Hartmann R, Kessler H, Sandhoff K. Expression of the GM2-activator protein in the methylotrophic yeast Pichia pastoris, purification, isotopic labeling, and biophysical characterization. Protein Expr Purif 2004; 34:147-57. [PMID: 14766311 DOI: 10.1016/j.pep.2003.11.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2003] [Revised: 11/13/2003] [Indexed: 11/18/2022]
Abstract
The GM2-activator protein (GM2AP) belongs to a group of five small, nonenzymatic proteins that are essential cofactors for the degradation of glycosphingolipids in the lysosome. It mediates the interaction between the water-soluble enzyme beta-hexosaminidase A and its membrane-embedded substrate, ganglioside GM2, at the lipid-water interphase. Inherited defects in the gene encoding this glycoprotein cause a fatal neurological storage disorder, the AB variant of GM2 gangliosidosis. With the aim to establish a convenient eukaryotic system that allows the efficient production of functionally folded, glycosylated GM2AP and offers the potential of cost-efficient isotopic labeling for structural studies by NMR spectroscopy, we established the expression of recombinant GM2AP in the methylotrophic yeast Pichia pastoris. For the construction of expression plasmids, either the full cDNA encoding human GM2AP preproprotein was cloned in the expression vector pPIC3.5K, or the cDNA encoding only the mature form of GM2AP was inserted in the vector pPIC9K under control of the alcohol oxidase 1 promoter. Both plasmids led to the successful secretory expression of active, glycosylated GM2AP, which could easily be purified by Ni-NTA chromatography due to the hexahistidine tag introduced at the C-terminus. Remarkably, the expression of this membrane-active protein in P. pastoris was accompanied by two peculiarities which were not encountered in other expression systems for GM2AP: First, a significant fraction of the secreted protein existed in the form of aggregates, and second, considerable amounts of noncovalently bound lipids were associated with the recombinant protein. A three-step purification scheme was therefore devised consisting of Ni-NTA, reversed phase, and gel filtration chromatography, which finally yielded 10-12 mg of purified, monomeric GM2AP per liter of expression supernatant. MALDI- and ESI-TOF mass spectrometry were employed to assess the processing, homogeneity, and glycosylation pattern of the recombinant protein. Surface plasmon resonance spectroscopy allowed the interaction of GM2AP with immobilized liposomes to be studied. A modified version of FM22 minimal medium was then used in the cost-effective (15)N-labeling of GM2AP to assess its amenability for the structural investigation by NMR spectroscopy. Initial (15)N,(1)H-HSQC experiments show a well-folded protein and provide evidence for extensive conformational exchange processes within the molecule.
Collapse
MESH Headings
- Chromatography/methods
- Chromatography, Gel
- Chromatography, Thin Layer
- DNA, Complementary/genetics
- Electrophoresis, Polyacrylamide Gel
- G(M2) Activator Protein
- G(M2) Ganglioside/metabolism
- Gene Expression/drug effects
- Gene Expression/genetics
- Genetic Vectors/genetics
- Glycosylation
- Humans
- Lipids/analysis
- Liposomes/chemistry
- Liposomes/metabolism
- Methanol/pharmacology
- Nitrogen Isotopes
- Nuclear Magnetic Resonance, Biomolecular
- Pichia/genetics
- Polysaccharides/chemistry
- Protein Biosynthesis
- Proteins/chemistry
- Proteins/isolation & purification
- Recombinant Proteins/biosynthesis
- Recombinant Proteins/chemistry
- Recombinant Proteins/isolation & purification
- Spectrometry, Mass, Electrospray Ionization
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
- Surface Plasmon Resonance
- Transformation, Genetic
- beta-N-Acetylhexosaminidases/metabolism
Collapse
Affiliation(s)
- Michaela Wendeler
- Kekulé-Institut für Organische Chemie und Biochemie, Gerhard-Domagk-Strasse 1, Bonn D-53121, Germany
| | | | | | | | | | | | | | | | | |
Collapse
|
18
|
Kang SJ, Cresswell P. Saposins facilitate CD1d-restricted presentation of an exogenous lipid antigen to T cells. Nat Immunol 2004; 5:175-81. [PMID: 14716312 DOI: 10.1038/ni1034] [Citation(s) in RCA: 169] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2003] [Accepted: 12/19/2003] [Indexed: 11/09/2022]
Abstract
Members of the CD1 family present antigenic lipids to T lymphocytes. CD1 molecules survey endocytic compartments for lipid antigens that are sorted into these vesicles after incorporation into the membrane bilayer, and extraction from the bilayer is likely to be a critical step for lipid association. We hypothesized that lysosomal saposins, which are cofactors required for sphingolipid degradation, might be involved in this process. Here we show that saposins, although not required for the autoreactive recognition of CD1d by natural killer T cells, are indispensable for the binding of an exogenous lipid antigen, alpha-galactosylceramide, to CD1d in the endocytic pathway. We suggest that saposins mobilize monomeric lipids from lysosomal membranes and facilitate their association with CD1d.
Collapse
Affiliation(s)
- Suk-Jo Kang
- Howard Hughes Medical Institute, Section of Immunobiology, Yale University School of Medicine, PO Box 208011, New Haven, CT 06520-8011, USA
| | | |
Collapse
|
19
|
Affiliation(s)
- Su-Chen Li
- Department of Biochemistry, Tulane University Health Sciences Center, School of Medicine, 1430 Tulane Avenue, New Orleans, Louisiana 70112, USA
| | | | | |
Collapse
|
20
|
Wendeler M, Lemm T, Weisgerber J, Hoernschemeyer J, Bartelsen O, Schepers U, Sandhoff K. Expression of recombinant human GM2-activator protein in insect cells: purification and characterization by mass spectrometry. Protein Expr Purif 2003; 27:259-66. [PMID: 12597885 DOI: 10.1016/s1046-5928(02)00599-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The GM2-activator protein (GM2AP) is a small non-enzymatic cofactor assisting the enzyme beta-hexosaminidase A in the lysosomal degradation of ganglioside GM2. Mutations in the gene encoding this glycoprotein lead to a fatal neurological disorder, the AB variant of GM2-gangliosidoses. In this paper, we describe the overexpression of GM2AP in Sf21 cells using both the baculovirus expression vector system (BEVS) and a non-lytic, plasmid-based insect cell expression system (InsectSelect). For the BEVS, the cDNA encoding human GM2AP-preproprotein was cloned in the expression vector pAcMP3. The recombinant virus generated by cotransfection with linearized baculovirus DNA was used to infect Sf21 cells. For the non-lytic expression system, the cDNA of GM2AP was inserted into the vector pIZ/V5-His, which was used for the constitutive expression in stably transformed Sf21 cells. As it was shown by immunoblot analysis of the cell culture supernatant, in both expression systems the GM2AP precursor protein was efficiently secreted into the medium. Following expression in the BEVS, the GM2AP was purified by sequential chromatography on Ni-NTA-agarose and Con A-Sepharose, resulting in a yield of up to 9 mg purified protein from 1L of cell culture supernatant. Following expression in stably transformed insect cells, the secreted protein was first concentrated by cation-exchange and purified by metal-ion affinity chromatography, with a yield of 0.1 mg/L cell culture supernatant. The biological activity of the recombinant protein was demonstrated by its ability to stimulate the hexosaminidase A-catalyzed degradation of ganglioside GM2, and the homogeneity and glycosylation were assessed by ESI-TOF mass spectrometry. While the protein expression in the BEVS led to partly glycosylated and partly non-glycosylated protein, the stably transformed cells produced only glycosylated protein. In both expression systems, the glycosylation was found to be identical and corresponded to the structure (GlcNAc)(2)Fuc(Man)(3).
Collapse
Affiliation(s)
- Michaela Wendeler
- Kekulé-Institut für Organische Chemie und Biochemie, Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany
| | | | | | | | | | | | | |
Collapse
|
21
|
Shimada Y, Li YT, Li SC. Effect of GM2 activator protein on the enzymatic hydrolysis of phospholipids and sphingomyelin. J Lipid Res 2003; 44:342-8. [PMID: 12576516 DOI: 10.1194/jlr.m200234-jlr200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
GM2 activator protein (GM2AP) is a specific protein cofactor that stimulates the enzymatic hydrolysis of the GalNAc from GM2, a sialic acid containing glycosphingolipid, both in vitro and in lysosomes. While phospholipids together with glycosphingolipids are important membrane constituents, little is known about the possible effect of GM2AP on the hydrolysis of phospholipids. Several recent reports suggest that GM2AP might have functions other than stimulating the conversion of GM2 into GM3 by beta-hexosaminidase A, such as inhibiting the activity of platelet activating factor and enhancing the degradation of phosphatidylcholine by phospholipase D (PLD). We therefore examined the effect of GM2AP on the in vitro hydrolyses of a number of phospholipids and sphingomyelin by microbial (Streptomyces chromofuscus) and plant (cabbage) PLD. GM2AP, at the concentration as low as 1.08 microM (1 microg/50 microl) was found to inhibit about 70% of the hydrolyses of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol by PLD, whereas the same concentration of GM2AP only inhibited about 20-25% of the hydrolysis of sphingomyelin by sphingomyelinase and had no effect on the hydrolysis of sphingosylphosphorylcholine by PLD. Thus, GM2AP exerts strong and broad inhibitory effects on the hydrolysis of phospholipids carried out by plant and microbial PLDs. High ammonium sulfate concentration (1.6 M or 21.1%) masks this inhibitory effect, possibly due to the alteration of the ionic property of GM2AP.
Collapse
Affiliation(s)
- Yoshimi Shimada
- Department of Biochemistry, Tulane University Health Sciences Center School of Medicine, New Orleans, LA 70112, USA
| | | | | |
Collapse
|
22
|
Schuette CG, Pierstorff B, Huettler S, Sandhoff K. Sphingolipid activator proteins: proteins with complex functions in lipid degradation and skin biogenesis. Glycobiology 2001; 11:81R-90R. [PMID: 11445546 DOI: 10.1093/glycob/11.6.81r] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Sphingolipid activator proteins (SAPs or saposins) are essential cofactors for the lysosomal degradation of membrane-anchored sphingolipids. Four of the five known proteins of this class, SAPs A--D, derive from a single precursor protein and show high homology, whereas the fifth protein, GM2AP, is larger and displays a different secondary structure. Although the main function of all five proteins is assumed to lie in the activation of lipid degradation, their specificities and modes of action seem to differ considerably. It has recently been demonstrated that the action of the proteins is highly enhanced by the presence of acidic lipids in the target membranes. These results have some interesting implications for the topology of lysosomal degradation of lipids and may provide new insights into the function of these interesting proteins, which are ubiquitously expressed in the different tissues of the body. Recent studies indicated that the SAPs play an important role in the biogenesis of the epidermal water barrier, which has been demonstrated by the analysis of the skin phenotype displayed by SAP-knockout mice. The results obtained so far have led to some new insights into the formation of the epidermal water permeability barrier and may lead to a better understanding of this complex process.
Collapse
Affiliation(s)
- C G Schuette
- Max-Planck-Institut fuer Biophysikalische Chemie, Abt. Neurobiologie, Am Fassberg 11, D-37077 Goettingen, Germany
| | | | | | | |
Collapse
|
23
|
Faull KF, Johnson J, Kim MJ, To T, Whitelegge JP, Stevens RL, Fluharty CB, Fluharty AL. Structure of the asparagine-linked sugar chains of porcine kidney and human urine cerebroside sulfate activator protein. JOURNAL OF MASS SPECTROMETRY : JMS 2000; 35:1416-1424. [PMID: 11180632 DOI: 10.1002/1096-9888(200012)35:12<1416::aid-jms75>3.0.co;2-k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The specific sugar residues and their linkages in the oligosaccharides from pig kidney and human urine cerebroside sulfate activator proteins (saposin B), although previously hypothesized, have been unambiguously characterized. Exhaustive sequential exoglycosidase digestion of the trimethyl-p-aminophenyl derivatives, followed by either matrix-assisted laser desorption/ionization and/or mass spectrometry, was used to define the residues and their linkages. The oligosaccharides were enzymatically released from the proteins by treatment with peptidyl-N-glycosidase F and separated from the proteins by reversed-phase high-performance liquid chromatography (HPLC). Reducing termini were converted to the trimethyl-p-aminophenyl derivative and the samples were further purified by normal-phase HPLC. The derivatized carbohydrates were then treated sequentially with a series of exoglycosidases of defined specificity, and the products of each digestion were examined by mass spectrometry. The pentasaccharides from pig kidney and human urine protein were shown to be of the asparagine-linked complex type composed of mannose-alpha 1-6-mannose-beta 1-4-N-acetylglucosamine-N-acetylglucosamine(alpha 1-6-fucose). This highly degraded structure probably represents the final product of intra-lysosomal exoglycosidase digestion. Oligosaccharide sequencing by specific exoglycosidase degradation coupled with mass spectrometry is more rapid than conventional oligosaccharide sequencing. The procedures developed will be useful for sequencing other oligosaccharides including those from other members of the lipid-binding protein class to which cerebroside sulfate activator belongs. (c) 2000 John Wiley & Sons, Ltd.
Collapse
Affiliation(s)
- K F Faull
- Department of Chemistry and Biochemistry, UCLA, Los Angeles, California, 90095, USA.
| | | | | | | | | | | | | | | |
Collapse
|
24
|
Wendeler M, Kolter T, Sandhoff K. Pathology of Glycosphingolipid Metabolism: The Molecular and Cellular Basis of Neurodegenerative Disease. Neuroscientist 2000. [DOI: 10.1177/107385840000600411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Glycosphingolipids are ubiquitous constituents of eukaryotic plasma membranes. Genetically determined deficiencies in their catabolic pathways cause the excessive intralysosomal accumulation of these lipids and give rise to a group of inherited metabolic diseases, the sphingolipidoses. The progression of these disorders often involves severe degeneration of the nervous system, and for nearly all of them, no effective treatment is available to date. Here, we discuss the physiological functions of glycosphingolipids and the topology and mechanism of their metabolism. The molecular defects associated with these storage disorders as well as their pathophysiological consequences and potential therapeutic prospects are presented. Finally, the importance of recently available animal models for the investigation of pathogenesis and the evaluation of future therapy approaches is discussed.
Collapse
Affiliation(s)
- Michaela Wendeler
- Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Bonn, Germany
| | - Thomas Kolter
- Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Bonn, Germany
| | - Konrad Sandhoff
- Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Bonn, Germany
| |
Collapse
|
25
|
Affiliation(s)
- U Bierfreund
- Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Germany
| | | | | |
Collapse
|
26
|
Faull KF, Whitelegge JP, Higginson J, To T, Johnson J, Krutchinsky AN, Standing KG, Waring AJ, Stevens RL, Fluharty CB, Fluharty AL. Cerebroside sulfate activator protein (Saposin B): chromatographic and electrospray mass spectrometric properties. JOURNAL OF MASS SPECTROMETRY : JMS 1999; 34:1040-1054. [PMID: 10510427 DOI: 10.1002/(sici)1096-9888(199910)34:10<1040::aid-jms863>3.0.co;2-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Cerebroside sulfate activator protein is a small, heat-stable protein that is exceptionally resistant to proteolytic attack. This protein is essential for the catabolism of cerebroside sulfate and several other glycosphingolipids. Protein purified from pig kidney and human urine was extensively characterized by reversed-phase liquid chromatography and electrospray mass spectrometry. These two sources revealed 20 and 18 different molecular isoforms of the protein, respectively. Plausible explanations of the structures of the majority of these isoforms can be made on the basis of accurate molecular mass assignments. The reversed-phase chromatographic and electrospray mass spectrometric properties of enzymatically deglycosylated and disulfide-reduced protein were also compared. In addition to a demonstration of the power of electrospray ionization mass spectrometry for revealing a wealth of information on protein microheterogeneity and structural detail, the results also demonstrate the utility of this technique for monitoring spontaneous chemical and enzymatically mediated changes that occur as a result of metabolic processing and protein purification.
Collapse
Affiliation(s)
- K F Faull
- Pasarow Mass Spectrometry Laboratory, Department of Psychiatry and Biobehavioral Sciences and the Neuropsychiatric Institute and Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095, USA.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
27
|
Affiliation(s)
- Y T Li
- Department of Biochemistry, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA
| | | |
Collapse
|
28
|
Abstract
Glycosphingolipids form cell type-specific patterns on the surface of eukaryotic cells. Degradation of glycosphingolipids requires endocytic membrane flow of plasma membrane-derived glycosphingolipids into the lysosomes as the digesting organelles. The inherited deficiencies of lysosomal hydrolases and of sphingolipid activator proteins both give rise to sphingolipid storage diseases. Recent research has focused on the mechanisms leading to selective membrane degradation in the lysosomes and on the mechanism and physiological function of sphingolipid activator proteins. The GM2-degrading system is a paradigm for activator protein-dependent lysosomal degradation. Three polypeptide chains contribute to the in vivo degradation of ganglioside GM2: the alpha- and beta-chains of the beta-hexosaminidases and the GM2 activator. Mouse models of Tay-Sachs disease (alpha-chain deficiency), Sandhoff disease (beta-chain deficiency) and GM2 activator deficiency have been described. While the phenotypes of these variants of GM2-gangliosidoses are only slightly different in humans, the animal models show drastic differences in severity and course of the diseases. The reason for this is the specificity of sialidase, which is different between mouse and human. A double-knockout mouse lacking beta-hexosaminidases A, B and S shows a phenotype of mucopolysaccharidosis and gangliosidosis. A substrate deprivation approach to therapy is discussed with respect to animal models of the GM2-gangliosidoses.
Collapse
Affiliation(s)
- T Kolter
- Keluké-Institut für Organische Chemie und Biochemie der Universität, Bonn, Germany
| | | |
Collapse
|
29
|
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.
Collapse
Affiliation(s)
- D J Mahuran
- Research Institute, The Hospital for Sick Children, 555 University Ave, Toronto, Ont. M5G 1X8, Canada.
| |
Collapse
|
30
|
Sandhoff K, Kolter T, Van Echten-Deckert G. Sphingolipid metabolism. Sphingoid analogs, sphingolipid activator proteins, and the pathology of the cell. Ann N Y Acad Sci 1998; 845:139-51. [PMID: 9668348 DOI: 10.1111/j.1749-6632.1998.tb09667.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Sphingolipid metabolism and function was investigated using sphingoid analogs, cells from human sphingolipidoses patients, and knockout animals. Treatment of primary cultured murine cerebellar cells with the structurally modified sphingosine base cis-4 methylsphingosine resulted in decreased sphingolipid biosynthesis accompanied by significant morphological changes. Plasma-membrane-derived glycosphingolipids (GSLs) destined for digestion are internalized through the endocytic pathway and delivered to lysosomes. There, GSLs are degraded by the action of exohydrolases, which are supported, in the case of GSLs with short oligosaccharide chains, by sphingolipid activator proteins (SAPs or saposins). The inherited deficiency of activators give rise to sphingolipid storage diseases. The analysis of cultured fibroblasts from corresponding patients suggests a new model for the topology of endocytosis and lysosomal digestion. Mice with disrupted genes for activator proteins and for GM2 degrading hexosaminidases turned out to be useful models for human diseases.
Collapse
Affiliation(s)
- K Sandhoff
- Kekulé-Institut für Organische Chemie und Biochemie der Universität, Bonn, Germany.
| | | | | |
Collapse
|
31
|
Abstract
Glycosphingolipids are ubiquitous membrane components of eukaryotic cells. They participate in various cell recognition events and can regulate enzymes and receptors within the plasma membrane. Sphingolipidoses are due to an impaired lysosomal digestion of these substances. Glycosphingolipids are degraded by the action of exohydrolases, which are supported, in the case of glycosphingolipids with short oligosaccharide chains, by sphingolipid activator proteins. Five sphingolipid activator proteins are known so far, the GM2-activator and the SAPs, SAP-A to D (also called saposins). Degradation of glycosphingolipids requires endocytic membrane flow of plasma membrane derived glycosphingolipids into the lysosomes. Recent research focused on the topology of this process and on the mechanism and physiological function of sphingolipid activator proteins. Limited knowledge is available about enzymology and topology of glycosphingolipid biosynthesis. Recently, intermediates of this metabolic pathway have been identified as novel signalling molecules. Inhibition of glycosphingolipid biosynthesis has been shown to be beneficial in the animal model of Tay-Sachs disease. Mice with disrupted genes for lysosomal hydrolases and activator proteins are useful models for known human diseases and are valuable tools for the study of glycosphingolipid metabolism, the pathogenesis of sphingolipidoses and novel therapeutic approaches.
Collapse
Affiliation(s)
- Thomas Kolter
- KekuléInstitut für Organische Chemie und Biochemie der Universität, Bonn, Germany
| | - Konrad Sandhoff
- KekuléInstitut für Organische Chemie und Biochemie der Universität, Bonn, Germany
| |
Collapse
|
32
|
Waring AJ, Chen Y, Faull KF, Stevens R, Sherman MA, Fluharty AL. Porcine cerebroside sulfate activator (saposin B) secondary structure: CD, FTIR, and NMR studies. Mol Genet Metab 1998; 63:14-25. [PMID: 9538512 DOI: 10.1006/mgme.1997.2646] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cerebroside sulfate activator protein (CSAct or saposin B) is one of a group of heat stable, low-molecular-weight proteins that appear to share a common structural motif. These have been referred to as saposin-like proteins and are thought to share a multiple amphipathic helical barrel structure with a conserved pattern of disulfide linkages. Porcine kidney CSAct was prepared in high purity and consisted of three major glycosylated subforms. The protein was studied by physical-chemical methods and evaluated by various methods for structural prediction. All suggest that CSAct has high amounts of alpha-helical conformation and little if any beta-sheet. Circular dichroism (CD) studies indicate 45-50% helical conformation depending on buffer and temperature. There was only a moderate loss in helical content with increasing temperature and no indication of thermal denaturation. Fourier transform infrared spectroscopy (FTIR) measurements on deuterium hydrated self-films also indicated a predominantly helical structure. Helical axis orientation was investigated by both oriented CD and FTIR dichroism, which suggested that the helical axes were roughly parallel and oriented along the axis of the surface on which the self-films had been deposited. One-dimensional nuclear magnetic resonance spectra showed large chemical shift dispersion, indicating a defined tertiary structure with little variation between 6 and 85 degrees C. NOESY spectra failed to show the strong NOE cross peaks expected for a highly helical conformation. This may indicate short-term conformational flexibility within the helices or molecular aggregation at the high protein concentrations employed. These observations are consistent with the 3-4-helix bundle motif suggested for saposin-like proteins by various predictive algorithms.
Collapse
Affiliation(s)
- A J Waring
- Department of Pediatrics, Drew University-King Medical Center/University of California Los Angeles 90059, USA
| | | | | | | | | | | |
Collapse
|
33
|
Marzella L, Lee HK. Chapter 5 Role of lysosomes in cell injury. PRINCIPLES OF MEDICAL BIOLOGY A MULTI-VOLUME WORK, VOLUME 13 1998. [PMCID: PMC7149001 DOI: 10.1016/s1569-2582(98)80007-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Lysosomes are acidic intracellular vacuoles of heterogeneous shape, size, and content. Lysosomes contain hydrolytic enzymes that degrade proteins, lipids, carbohydrates, and nucleic acids derived from intracellular (through autophagy) and extracellular (through heterophagy) sources. Lysosomal degradation regulates several physiological cell functions. These include turnover of cellular organelles and extracellular constituents; amino acid and glucose homeostasis; processing of proteins; lipid metabolism; cell growth, differentiation, and involution; host defenses against microorganisms and other pathogens; and removal of necrotic and foreign material from the circulation and from tissues. Lysosomal degradation also plays an important role in the pathophysiology of acute and chronic cell injury, inflammation and repair, and tumor growth and metastasis. The participation of the lysosomes in the specific types of cell injury we have discussed is due to altered regulation of one or more of the following processes: turnover of cellular organelles by autophagic degradation; levels and activities of lysosomal hydrolases; levels of intracellular and extracellular lysosomal hydrolase inhibitors; transport of degradation products from the lysosomal matrix to the cytosol; permeability of the lysosomal membrane to hydrolases; lysosomal vacuolar acidification; transport of degradable substrates and of pathogens to the lysosomes; transport and processing of secretory proteins and lysosomal hydrolases during biogenesis; traffic and fusion of lysosomal vacuoles and vesicles; secretion of lysosomal hydrolases; and accumulation of metals, particularly iron, acidotropic agents, and undegraded and/or undegradable materials in lysosomes.
Collapse
|
34
|
Abstract
Glycosphingolipids (GSLs) form cell-type-specific patterns on the surface of eukaryotic cells. Degradation of GSLs requires endocytotic membrane flow of plasma membrane-derived GSLs into the lysosomes as the digesting organelles. Recent research focused on the mechanisms leading to selective membrane degradation in the lysosomes and on the mechanism and physiological function of sphingolipid activator proteins, which are needed for degradation of GSLs with short oligosaccharide chains in addition to hydrolysing enzymes. Both, the inherited deficiency of lysosomal hydrolases and of sphingolipid activator proteins give rise to sphingolipid storage diseases. In some cases it was possible to correlate residual enzyme activities with the onset and the course of the disease.
Collapse
Affiliation(s)
- K Sandhoff
- Kekulé-Institut für Organische Chemie und Biochemie der Universität, Bonn, Germany.
| | | |
Collapse
|
35
|
Riboni L, Viani P, Bassi R, Prinetti A, Tettamanti G. The role of sphingolipids in the process of signal transduction. Prog Lipid Res 1997; 36:153-95. [PMID: 9624426 DOI: 10.1016/s0163-7827(97)00008-8] [Citation(s) in RCA: 150] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- L Riboni
- Department of Medical Chemistry and Biochemistry, Medical Faculty, University of Milan, Italy
| | | | | | | | | |
Collapse
|
36
|
Abstract
GM2 activator protein is a protein cofactor that has been shown to stimulate the enzymatic hydrolysis of both GalNAc and NeuAc from GM2 (Wu, Y. Y., Lockyer, J. M., Sugiyama, E., Pavlova, N.V., Li, Y.-T., and Li, S.-C. (1994) J. Biol. Chem. 269, 16276-16283). To understand the mechanism by which GM2 activator stimulates the hydrolysis of GM2, we examined the interaction of this activator protein with GM2 as well as with other glycosphingolipids by TLC overlay and Sephacryl S-200 gel filtration. The TLC overlay analysis unveiled the binding specificity of GM2 activator, which was not previously revealed. Under the conditions optimal for the activator protein to stimulate the hydrolysis of GM2 by beta-hexosaminidase A, GM2 activator was found to bind avidly to acidic glycosphingolipids, including gangliosides and sulfated glycosphingolipids, but not to neutral glycosphingolipids. The gangliosides devoid of sialic acids, such as asialo-GM1 and asialo-GM2, and the GM2 derivatives whose carboxyl function in the NeuAc had been modified by methyl esterification or reduction, were only very weakly bound to GM2 activator. These results indicate that the negatively charged sugar residue or sulfate group in gangliosides is one of the important sites recognized by GM2 activator. For comparison, we also studied in parallel the complex formation between glycosphingolipids and saposin B, a separate activator protein with broad specificity to stimulate the hydrolysis of various glycosphingolipids. We found that saposin B bound to neutral glycosphingolipids and gangliosides equally well, and there was an exceptionally strong binding to sulfatide. In contrast to previous reports, we found that GM2 activator formed complexes with GM2 and other gangliosides in different proportions depending on the ratio between the activator protein and the ganglioside in the incubation mixture prior to gel filtration. We were not able to detect the specific binding of GM2 activator to GM2 when GM2 was mixed with GM1 or GM3. Thus, the specificity or the mode of action of GM2 activator cannot be simply explained by its interaction with glycosphingolipids based on complex formation. The binding of GM2 activator to a wide variety of negatively charged glycosphingolipids may indicate that this activator protein has functions other than assisting the enzymatic hydrolysis of GM2.
Collapse
Affiliation(s)
- Y Hama
- Department of Biochemistry, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA
| | | | | |
Collapse
|
37
|
Haltia A, Solin ML, Jalanko H, Holmberg C, Miettinen A, Holthöfer H. Sphingolipid activator proteins in a human hereditary renal disease with deposition of disialogangliosides. THE HISTOCHEMICAL JOURNAL 1996; 28:681-7. [PMID: 8950597 DOI: 10.1007/bf02409005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Congenital nephrotic syndrome of the Finnish type is a recessively inherited renal disease with glomerular deposits of the disialoganglioside O-acetyl-GD3. Sphingolipid activator proteins (saposins) stimulate the degradation of glycosphingolipids by lysosomal enzymes, and defects in saposins cause accumulation of substrate lipids in the affected tissues in lysosomal storage disease. Here we report a study of the role of saposins in the accumulation of O-acetyl-GD3 in kidneys of congenital nephrotic syndrome patients. At the mRNA level, the expression of saposin precursor in diseased kidneys appeared normal, and the nucleotide sequence analysis of cDNA clones did not reveal abnormalities in the prosaposin gene. Immunohistologically, saposins were localized mainly to the epithelial cells of the distal renal tubules or to the parietal epithelial cells of glomeruli. In the nephrotic syndrome kidneys, the staining pattern was highly granular and appeared mostly in the apical part of the epithelial lining, unlike the control kidneys. These results show that a major site of ganglioside metabolism is located in the distal nephron. Furthermore, these results suggest that saposins are not directly involved in the metabolism of the terminal sialic acids of disialogangliosides in the nephrotic syndrome kidneys.
Collapse
Affiliation(s)
- A Haltia
- Department of Bacteriology and Immunology, University of Helsinki, Finland
| | | | | | | | | | | |
Collapse
|
38
|
Wu YY, Sonnino S, Li YT, Li SC. Characterization of an alternatively spliced GM2 activator protein, GM2A protein. An activator protein which stimulates the enzymatic hydrolysis of N-acetylneuraminic acid, but not N-acetylgalactosamine, from GM2. J Biol Chem 1996; 271:10611-5. [PMID: 8631864 DOI: 10.1074/jbc.271.18.10611] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
GM2 activator protein is a protein cofactor which stimulates the enzymatic hydrolysis of both GalNAc and NeuAc from GM2. We have previously isolated two cDNA clones, GM2 activator cDNA and GM2A cDNA, for human GM2 activator protein (Nagarajan, S., Chen, H.-C., Li, S.-C., Li, Y.-T., and Lockyer, J. M. (1992) Biochem. J. 282, 807-813). GM2A mRNA is an RNA alternative splicing product that contains exons 1, 2, 3, and intron 3 of the genomic DNA sequence of GM2 activator protein (Klima, H., Tanaka, A., Schnabel, D., Nakano, T., Schröder, M., Suzuki, K., and Sandhoff, K. (1991) FEBS Lett. 289, 260-264). GM2A cDNA encodes a protein (GM2A protein) containing 1-109 of the 160 amino acids of human GM2 activator protein, plus a tripeptide (VST) encoded by intron 3 at the COOH terminus. Thus, GM2A protein can be regarded as a form (truncated version) of GM2 activator protein. We have expressed GM2A cDNA in Escherichia coli using pT7-7 as the vector. The recombinant GM2A protein was purified to an electrophoretically homogeneous form and was found to stimulate the hydrolysis of NeuAc from GM2 by clostridial sialidase, but not the hydrolysis of GalNAc from GM2 by beta-hexosaminidase A. Like GM2 activator protein, GM2A protein also specifically recognized the terminal GM2 epitope in GalNAc-GD1a and stimulated the hydrolysis of only the external NeuAc from this ganglioside by clostridial sialidase. These results enabled us to discern the enzymatic hydrolyses of GalNAc and NeuAc from the GM2 epitope and established that the NeuAc recognition domain of GM2 activator protein is located within amino acids 1-109. The presence of GM2A mRNA in human tissues and the selective stimulation of NeuAc hydrolysis by GM2A protein indicate that this activator protein may be involved in the catabolism of GM2 through the asialo-GM2 pathway.
Collapse
Affiliation(s)
- Y Y Wu
- Department of Biochemistry, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA
| | | | | | | |
Collapse
|
39
|
Abstract
Glycosphingolipids (GSLs) form cell-type-specific patterns on the surface of eukaryotic cells. Degradation of plasma-membrane-derived GSLs in the lysosomes after internalization through the endocytic pathway is achieved through the concerted actions of hydrolysing enzymes and sphingolipid activator proteins. The latter are proteins necessary for the degradation of GSLs possessing short oligosaccharide chains. Some activator proteins bind to GSLs and form water-soluble complexes, which lift out of the membrane and give the water-soluble hydrolysing enzymes access to the regions of the GSL that would otherwise be obscured by the membrane. The inherited deficiency of both lysosomal hydrolases and sphingolipid activator proteins gives rise to sphingolipid storage diseases. An analysis of these diseases suggests a new model for the topology of endocytosis and lysosomal digestion, which is discussed in this article.
Collapse
Affiliation(s)
- K Sandhoff
- Institut für Organische Chemie und Biochemie der Universität, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
| | | |
Collapse
|
40
|
Li SC, Wu YY, Sugiyama E, Taki T, Kasama T, Casellato R, Sonnino S, Li YT. Specific recognition of N-acetylneuraminic acid in the GM2 epitope by human GM2 activator protein. J Biol Chem 1995; 270:24246-51. [PMID: 7592631 DOI: 10.1074/jbc.270.41.24246] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
GM2 Activator is a low molecular weight protein cofactor that stimulates the enzymatic conversion of GM2 into GM3 by human beta-hexosaminidase A and also the conversion of GM2 into GA2 by clostridial sialidase (Wu, Y.-Y., Lockyer, J.M., Sugiyama, E., Pavlova, N.V., Li, Y.-T., and Li, S.-C. (1994) J. Biol. Chem. 269, 16276-16283). Among the five known activator proteins for the enzymatic hydrolysis of glycosphingolipids, only GM2 activator is effective in stimulating the hydrolysis of GM2. However, the mechanism of action of GM2 activator is still not well understood. Using a unique disialosylganglioside, GalNAc-GD1a, as the substrate, we were able to show that in the presence of GM2 activator, GalNAc-GD1a was specifically converted into GalNAc-GM1a by clostridial sialidase, while in the presence of saposin B, a nonspecific activator protein, GalNAc-GD1a was converted into both GalNAc-GM1a and GalNAc-GM1b. Individual products generated from GalNAc-GD1a by clostridial sialidase were identified by thin layer chromatography, negative secondary ion mass spectrometry, and immunostaining with a monoclonal IgM that recognizes the GM2 epitope. Our results clearly show that GM2 activator recognizes the GM2 epitope in GalNAc-GD1a. Thus, GM2 activator may interact with the trisaccharide structure of the GM2 epitope and render the GalNAc and NeuAc residues accessible to beta-hexosaminidase A and sialidase, respectively.
Collapse
Affiliation(s)
- S C Li
- Department of Biochemistry, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA
| | | | | | | | | | | | | | | |
Collapse
|
41
|
Munford RS, Sheppard PO, O'Hara PJ. Saposin-like proteins (SAPLIP) carry out diverse functions on a common backbone structure. J Lipid Res 1995. [DOI: 10.1016/s0022-2275(20)41485-3] [Citation(s) in RCA: 153] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
|
42
|
Champagne MJ, Lamontagne S, Potier M. Binding of GM1 ganglioside to a synthetic peptide derived from the lysosomal sphingolipid activator protein saposin B. FEBS Lett 1994; 349:439-41. [PMID: 8050611 DOI: 10.1016/0014-5793(94)00717-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Saposin B is a lysosomal sphingolipid activator protein which activates GM1 ganglioside hydrolysis by lysosomal beta-galactosidase. To identify the structural elements of saposin B implicated in sphingolipid binding, we studied a synthetic peptide corresponding to a predicted alpha-helix, sapB-18, spanning residues 52-69 of saposin B. The circular dichroism spectrum of sapB-18 at pH 4.4 was consistent with a 44% alpha-helix content. As shown by intrinsic Tyr fluorescence studies of sapB-18, this peptide binds the GM1 ganglioside with a Kd of about 7 microM. Thus, we suggest that a putative amphipathic alpha-helix between residues 52 and 69 of saposin B plays a major role in the recognition and binding of GM1 ganglioside by saposin B.
Collapse
Affiliation(s)
- M J Champagne
- Service de Génétique Médicale, Hôpital Sainte-Justine, Montréal, Qué., Canada
| | | | | |
Collapse
|
43
|
Champagne MJ, Lamontagne S, Potier M. Binding of GM1-ganglioside to a synthetic peptide derived from the lysosomal sphingolipid-activator-protein saposin B. FEBS Lett 1994; 347:265-7. [PMID: 8034015 DOI: 10.1016/0014-5793(94)00536-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Saposin B is a lysosomal sphingolipid-activator-protein which activates GM1-ganglioside hydrolysis by lysosomal beta-galactosidase. To identify the structural elements of saposin B implicated in sphingolipid binding, we studied a synthetic peptide corresponding to a predicted alpha-helix, sapB-18, spanning residues 52 to 69 of saposin B. The circular dichroism spectrum of sapB-18 at pH 4.4 was consistent with a 44% alpha-helix content. As shown by intrinsic Tyr fluorescence studies of sapB-18, this peptide binds the GM1-ganglioside with a Kd of about 7 microM. Thus, we suggest that a putative amphipathic alpha-helix between residues 52 and 69 of saposin B plays a major role in the recognition and binding of GM1-ganglioside by saposin B.
Collapse
Affiliation(s)
- M J Champagne
- Service de Génétique Médicale, Hôpital Sainte-Justine, Montréal, Québec, Canada
| | | | | |
Collapse
|
44
|
Sandhoff K, Klein A. Intracellular trafficking of glycosphingolipids: role of sphingolipid activator proteins in the topology of endocytosis and lysosomal digestion. FEBS Lett 1994; 346:103-7. [PMID: 8206147 DOI: 10.1016/0014-5793(94)00282-7] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Glycosphingolipids (GSL) are components of the outer leaflet of the plasma membrane (PM) of vertebrate tissues. Our current knowledge of GSL metabolism and their intracellular traffic has been derived from metabolic studies but the exact mechanisms by which GSLs are transported from sites of synthesis (endoplasmic reticulum and Golgi) to the sites of residence (PM) and degradation (lysosomes) have not been clearly defined. It is now established that components of the PM reach the lysosomal compartment mainly by endocytic membrane flow. According to a new model, GSLs derived from the PM are thought to end up in intra-endosomal vesicles which could be delivered, by successive processes of membrane fission and fusion, along the endocytic pathway directly into the lumen of the lysosomes. Here the GSLs are degraded in a step-wise manner by exohydrolases. However, the catabolism of membrane-bound GSLs with short hydrophilic head groups needs the assistance of sphingolipid activator proteins (SAPs), which lift the GSLs from the plane of the membrane and present them for degradation to the lysosomal exohydrolases, which are usually water-soluble. The inherited deficiency of one of these enzymes or SAPs causes the lysosomal storage of their respective GSL substrates. In the case of the simultaneous deficiency of all 4 different SAPs the storage of all GSLs with short hydrophilic head groups occurs within multivesicular bodies and/or intra-lysosomal vesicles.
Collapse
Affiliation(s)
- K Sandhoff
- Institut für Organische Chemie und Biochemie, Universität Bonn, Germany
| | | |
Collapse
|
45
|
Wu Y, Lockyer J, Sugiyama E, Pavlova N, Li Y, Li S. Expression and specificity of human GM2 activator protein. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)34004-8] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
|
46
|
Novak A, Lowden JA. GM2 ganglioside activator occurs in multiple forms. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1199:209-14. [PMID: 8123670 DOI: 10.1016/0304-4165(94)90117-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The protein which activates the hydrolysis of GM2 ganglioside by hexosaminidase A was purified from human kidney. The GM2 activator had a molecular mass of 28 kDa by gel filtration and was resolved into three major bands using polyacrylamide gel electrophoresis in the presence of SDS with molecular masses of 23, 22 and 21 kDa. These three bands corresponded respectively to strongly binding, weakly binding and non-binding fractions of GM2 activator chromatographed through concanavalin A-Sepharose, indicating that GM2 activator exists in multiple glycosylated forms.
Collapse
Affiliation(s)
- A Novak
- Division of Neurosciences, Hospital for Sick Children, Toronto, Canada
| | | |
Collapse
|
47
|
Ponting CP. Acid sphingomyelinase possesses a domain homologous to its activator proteins: saposins B and D. Protein Sci 1994; 3:359-61. [PMID: 8003971 PMCID: PMC2142785 DOI: 10.1002/pro.5560030219] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
An N-terminal region of the acid sphingomyelinase sequence (residues 89-165) is shown to be homologous to saposin-type sequences. By analogy with the known functions of saposins, this sphingomyelinase saposin-type domain may possess lipid-binding and/or sphingomyelinase-activator properties. This finding may prove to be important in the understanding of Niemann-Pick disease, which results from sphingomyelinase deficiency.
Collapse
Affiliation(s)
- C P Ponting
- Department of Biochemistry, University of Oxford, United Kingdom
| |
Collapse
|
48
|
Sandhoff K, van Echten G. Ganglioside metabolism: enzymology, topology and regulation. PROGRESS IN BRAIN RESEARCH 1994; 101:17-29. [PMID: 8029449 DOI: 10.1016/s0079-6123(08)61937-8] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- K Sandhoff
- Institut für Organische Chemie und Biochemie, Universität Bonn, Germany
| | | |
Collapse
|
49
|
Stevens RL, Faull KF, Conklin KA, Green BN, Fluharty AL. Porcine cerebroside sulfate activator: further structural characterization and disulfide identification. Biochemistry 1993; 32:4051-9. [PMID: 8471613 DOI: 10.1021/bi00066a028] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Cerebroside sulfate activator (CS-Act) is a small compact protein which binds and solubilizes certain glycosphingolipids. Following the recent publication of the purification and preliminary sequence of pig kidney CS-Act [Fluharty, A.L., Katona, Z., Meek, W.E., Frei, K., & Fowler, A.V. (1992) Biochem. Med. Metab. Biol. 47, 66-85], we now report the primary sequence of the C-terminal portion of this protein and the assignment of the three disulfide bonds. Cyanogen bromide (CNBr) treatment of native CS-Act produced three major and several minor peptide fragments. Analysis of one HPLC-purified fragment revealed the C-terminus 14 amino acid sequence. This established the length of the native protein at 79 residues. In conjunction with the sequence data for one other major HPLC-purified CNBr fragment, it could be concluded that the three intrachain disulfide bonds were located at half-cystine residues 4 and 77, 7 and 71, and 36 and 47. Mass spectrometry (fast atom bombardment and electrospray ionization) showed the molecular weight of the major component of the CS-Act preparation to be 9720.5 Da, which was in close agreement with the calculated mass of the 79 amino acid peptide with five covalently attached sugar residues and three internal disulfide bonds. The mass spectrometric molecular weight measurements also showed that the CS-Act preparation possessed microheterogeneity in its carbohydrate moiety, as less intense signals corresponded to species containing (in decreasing order of abundance) two, one, four, and three sugar residues.(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- R L Stevens
- Department of Biological Chemistry, UCLA School of Medicine 90024
| | | | | | | | | |
Collapse
|
50
|
Tayama M, O'Brien JS, Kishimoto Y. Distribution of saposins (sphingolipid activator proteins) in tissues of lysosomal storage disease patients. J Mol Neurosci 1992; 3:171-5. [PMID: 1389998 DOI: 10.1007/bf03380135] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Saposins are a group of small glycoproteins derived from a single precursor protein, prosaposin. Each of the four saposins are involved in lysosomal hydrolysis of various sphingolipids. Our recent investigations have shown that saposins accumulate in tissues of several lysosomal storage diseases patients, including those with Tay-Sachs disease and Gaucher disease. To obtain insight into the mechanism of accumulation and its pathological role, the subcellular distribution of saposins in brain from Tay-Sachs disease and in spleen of Gaucher disease were compared with that of GM2 ganglioside and glucocerebroside, respectively. In both Tay-Sachs brain and Gaucher spleen, saposins were found predominantly in light-density fractions while most of the GM2 ganglioside and glucocerebroside, respectively, were found in heavy-density fractions. These studies indicate that saposins that accumulate in these pathological tissues are not tightly associated with GM2 ganglioside or glucocerebroside.
Collapse
Affiliation(s)
- M Tayama
- University of California, School of Medicine, Department of Neurosciences, San Diego, La Jolla 92093-0634
| | | | | |
Collapse
|