Occurrence of two molecular forms of human acid sphingomyelinase

Human acid sphingomyelinase (ASM) hydrolyses sphingomyelin to ceramide and phosphocholine. Metabolic studies on COS-1 cells transfected with ASM cDNA revealed the occurrence of an enzymically inactive precursor which is differentially processed to two predominant native glycoprotein forms: a 70 kDa polypeptide corresponding to human urinary protein and a 57 kDa form. Formation of these potentially active forms was shown to be restricted to distinct compartments. Maturation of the ASM precursor to a predominant 70 kDa form occurs exclusively inside acidic organelles, whereas variable amounts of 57 kDa ASM are detectable immediately after biosynthesis. Metabolic labelling of transfected COS-1 cells with [32P]Pi further suggests that this form obviously does not carry oligomannosylphosphate residues, in contrast with the mature lysosomal ASM. In order to verify that this early form of active ASM results from co-post-translational proteolysis of the ASM precursor and not from the use of different translation-initiation sites on the ASM mRNA, appropriate 5'-mutagenized cDNA constructs were transiently expressed. These results clearly indicate that the first potential in-frame AUG is exclusively used for translation initiation in vivo and that deletion of the proposed signal sequence for endoplasmic reticulum import completely eliminates the ability of the translation product to enter the vacuolar apparatus. As there are two different subcellular sites of maturation of the ASM precursor, and intracellular targeting of the two processed forms appears to be different, the two ASM proteins may contribute to distinct physiological functions

Sulfatide activator protein : alternative splicing that generates three mRNAs and a newly found mutation responsible for a clinical disease

The sulfatide activator protein, also known as SAP-1, is derived from a gene that generates an mRNA coding for four homologous proteins. Its physiological function is to stimulate hydrolysis of sulfatide by arylsulfatase A in vivo. A genetic defect in the sulfatide activator results in a metabolic disorder similar to classical metachromatic leukodystrophy, which is itself caused by a genetic defect in arylsulfatase A. In a patient with sulfatide activator deficiency, a nucleotide transversion G722----C (counted from A of the initiation codon ATG) was found in the mRNA of the sulfatide activator precursor, resulting in the substitution of serine for Cys241 in the mature sulfatide activator. The remainder of the coding sequence was completely normal except for a polymorphism C to T in position 1389, which does not change the amino acid sequence. The patient produces at least three different forms of mRNA for the precursor. Two of them include a stretch of an additional 9 and 6 bases, respectively, within the sulfatide activator coding region. In normal individuals this stretch of additional bases has also been observed. This could be explained by the presence of a small 9-base pair exon which can be introduced, or not, by alternative splicing as a stretch of 9 or 6 bases into the mature mRNA. The shortest form of the mRNA yields an active sulfatide activator (Fürst, W., Schubert, J., Machleidt, W., Meier, H. E., and Sandhoff, K. (1990) Eur. J. Biochem. 192, 709-714)

Over-expression of a functionally active human G M2 -activator protein in Escherichia coli

The cDNA of the human GM2-activator protein was cloned into the expression vector pHX17. The plasmid encodes a fusion protein with a hexahistidine tail and a Factor Xa cleavage site at its N-terminus. The recombinant protein was purified from cell homogenates under denaturing conditions by metal-ion affinity chromatography in a single step and then was refolded. The hexahistidine tail could be removed when desired by digestion with Factor Xa. In a functional assay, the GM2-activator thus generated from Escherichia coli and renatured, with or without the hexahistidine tail, was as active as the native GM2-activator protein that was purified from human tissue. When added to the culture medium, the recombinant carbohydrate-free GM2-activator, carrying the hexahistidine tail, could be taken up efficiently and restored the degradation of ganglioside GM2 to normal rates in mutant fibroblasts with the AB variant of GM2-gangliosidosis, which is characterized by a genetic defect in the GM2-activator protein. The prokaryotic expression system is useful for producing milligram quantities of a pure and functionally active GM2-activator

A Clathrin light chain A reporter mouse for in vivo imaging of endocytosis

Clathrin-mediated endocytosis (CME) is one of the best studied cellular uptake pathways and its contributions to nutrient uptake, receptor signaling, and maintenance of the lipid membrane homeostasis have been already elucidated. Today, we still have a lack of understanding how the different components of this pathway cooperate dynamically in vivo. Therefore, we generated a reporter mouse model for CME by fusing eGFP endogenously in frame to clathrin light chain a (Clta) to track endocytosis in living mice. The fusion protein is expressed in all tissues, but in a cell specific manner, and can be visualized using fluorescence microscopy. Recruitment to nanobeads recorded by TIRF microscopy validated the functionality of the Clta-eGFP reporter. With this reporter model we were able to track the dynamics of Alexa594-BSA uptake in kidneys of anesthetized mice using intravital 2-photon microscopy. This reporter mouse model is not only a suitable and powerful tool to track CME in vivo in genetic or disease mouse models it can also help to shed light into the differential roles of the two clathrin light chain isoforms in health and disease

Roles of hyaluronan in bone resorption

BACKGROUND: Hyaluronan, an unsulfated glycosaminoglycan, while being closely linked to osteoclast function several years ago, has received little attention lately. Given recent new knowledge of hyaluronan's possible cell binding abilities, it is important to re-examine the role of this polysaccharide in bone homeostasis. DISCUSSION: Previously published data demonstrating a linkage between induction of hyaluronan synthesis and osteoclast-mediated bone resorption are reviewed. Suggestions are made involving the cell binding ability of hyaluronan and its potential to mediate osteoclast binding to bone surfaces and its potential to serve as a diffusion barrier and participate in the sealing zone required for osteoclast-mediated bone resorption. SUMMARY: This brief article summarizes previous studies linking HA to bone resorption and suggests roles for hyaluronan in the process of bone resorption

Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13

Measurement of χ c1 and χ c2 production with s√ = 7 TeV pp collisions at ATLAS

The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at s√ = 7 TeV with the ATLAS detector at the LHC using 4.5 fb−1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c → J/ψγ (with J/ψ → μ + μ −) where photons are reconstructed from γ → e + e − conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured

Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at s√=8 TeV with ATLAS

Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The analysis is performed in the H → γγ decay channel using 20.3 fb−1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp → H → γγ fiducial cross section is measured to be 43.2 ±9.4(stat.) − 2.9 + 3.2 (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations