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  • 1.
    Eriksson, Hanna M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Wessman, Per
    Ge, Changrong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Edwards, Katarina
    Wieslander, Ake
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Massive formation of intracellular membrane vesicles in Escherichia coli by a monotopic membrane-bound lipid glycosyltransferase2009Inngår i: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 284, nr 49, s. 33904-33914Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The morphology and curvature of biological bilayers are determined by the packing shapes and interactions of their participant molecules. Bacteria, except photosynthetic groups, usually lack intracellular membrane organelles. Strong overexpression in Escherichia coli of a foreign monotopic glycosyltransferase (named monoglycosyldiacylglycerol synthase), synthesizing a nonbilayer-prone glucolipid, induced massive formation of membrane vesicles in the cytoplasm. Vesicle assemblies were visualized in cytoplasmic zones by fluorescence microscopy. These have a very low buoyant density, substantially different from inner membranes, with a lipid content of > or = 60% (w/w). Cryo-transmission electron microscopy revealed cells to be filled with membrane vesicles of various sizes and shapes, which when released were mostly spherical (diameter approximately 100 nm). The protein repertoire was similar in vesicle and inner membranes and dominated by the glycosyltransferase. Membrane polar lipid composition was similar too, including the foreign glucolipid. A related glycosyltransferase and an inactive monoglycosyldiacylglycerol synthase mutant also yielded membrane vesicles, but without glucolipid synthesis, strongly indicating that vesiculation is induced by the protein itself. The high capacity for membrane vesicle formation seems inherent in the glycosyltransferase structure, and it depends on the following: (i) lateral expansion of the inner monolayer by interface binding of many molecules; (ii) membrane expansion through stimulation of phospholipid synthesis, by electrostatic binding and sequestration of anionic lipids; (iii) bilayer bending by the packing shape of excess nonbilayer-prone phospholipid or glucolipid; and (iv) potentially also the shape or penetration profile of the glycosyltransferase binding surface. These features seem to apply to several other proteins able to achieve an analogous membrane expansion.

  • 2.
    Ge, Changrong
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Georgiev, Alexander
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Öhman, Anders
    Wieslander, Åke
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Kelly, Amélie A.
    Tryptophan residues promote membrane association for a plant lipid glycosyltransferase involved in phosphate stress2011Inngår i: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 286, nr 8, s. 6669-6684Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Chloroplast membranes contain a substantial excess of the nonbilayer-prone monogalactosyldiacylglycerol (GalDAG) over the biosynthetically consecutive, bilayer-forming digalactosyldiacylglycerol (GalGalDAG), yielding a high membrane curvature stress. During phosphate shortage, plants replace phospholipids with GalGalDAG to rescue phosphate while maintaining membrane homeostasis. Here we investigate how the activity of the corresponding glycosyltransferase (GT) in Arabidopsis thaliana (atDGD2) depends on local bilayer properties by analyzing structural and activity features of recombinant protein. Fold recognition and sequence analyses revealed a two-domain GT-B monotopic structure, present in other plant and bacterial glycolipid GTs, such as the major chloroplast GalGalDAG GT atDGD1. Modeling led to the identification of catalytically important residues in the active site of atDGD2 by site-directed mutagenesis. The DGD synthases share unique bilayer interface segments containing conserved tryptophan residues that are crucial for activity and for membrane association. More detailed localization studies and liposome binding analyses indicate differentiated anchor and substrate-binding functions for these separated enzyme interface regions. Anionic phospholipids, but not curvature-increasing nonbilayer lipids, strongly stimulate enzyme activity. From our studies, we propose a model for bilayer "control" of enzyme activity, where two tryptophan segments act as interface anchor points to keep the substrate region close to the membrane surface. Binding of the acceptor substrate is achieved by interaction of positive charges in a surface cluster of lysines, arginines, and histidines with the surrounding anionic phospholipids. The diminishing phospholipid fraction during phosphate shortage stress will then set the new GalGalDAG/phospholipid balance by decreasing stimulation of atDGD2.

  • 3.
    Ge, Changrong
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Raussens, Vincent
    Ruysschaert, Jean-Marie
    Wieslander, Åke
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Modulation of Escherichia coli Cell Membrane by a Monotopic Lipid Glycosyltransferase - an Exploration of Potential MechanismsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Intracellular vesicles are abundant in eukaryotic cells but are rare in Gram-negative bacterium Escherichia coli. Strongly overexpression of a monotopic glycolipid-synthesizing enzyme could induce massive formation of “foreign” vesicles in the cytoplasm. Here we investigate how this membrane-associated enzyme is able to bend and deform the plasma membrane. Limited proteolysis combined with ESI-MS suggested interface binding is mediated through both its two Rossmann fold topological domains. Detailed subcellular localization and liposome binding assay indicates different interface anchoring regions in the protein, and anionic lipid seems to influence the binding properties of the anchoring segments. Genetic engineering of a known membrane-bound segment to explore its vesiculation potentials led to the identification of important catalytic residues (regions). Flow cytometry and infrared spectroscopy were also performed on bacterial cells to get more insight into the cellular morphology and internal complexity. The linking region between two domains was demonstrated to be crucial for both catalytic function and vesiculation capacity of the enzyme. Based on our findings, we propose, that scaffold-like structural feature of this enzyme is most likey one of key elements contributing to vesiculation.        

  • 4.
    Georgiev, Alexander
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Ge, Changrong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Wieslander, Åke
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Basic clusters and amphipathic helices contribute to interactions of Myr1/Syh1 with membrane phospholipidsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The ability to associate transiently with membrane bilayers is an important property of many protein regulators of membrane trafficking, lipid transfer proteins, or signaling modules. Membrane association is also a property of Myr1/Syh1, a soluble GYF domain protein from Saccharomyces cerevisiae, previously reported to rescue the temperature sensitive growth of ypt6 and ric1 null strains. Here, we further demonstrate that MYR1 also rescued the vacuole fragmentation phenotype of the ypt6 and ric1 mutants. The mechanism behind these genetic interactions is likely linked to the capacity of the Myr1/Syh1 protein to associate with phospholipid membranes. In order to elucidate further the nature of the interactions with vesicular traffic, we studied protein-protein and protein-phospholipid association of isolated domains from Myr1/Syh1. Using a two-hybrid assay, we confirmed the capacity of Myr1/Syh1 to self-associate in vivo. We measured in vitro the affinity of recombinant Myr1/Syh1 domains fused to GFP for liposomes reconstituted from synthetic and natural yeast lipids by sedimentation techniques. The herewith established affinities of Myr1/Syh1 to specific lipids, combined with evidence for its interactions with membrane traffic and protein synthesis, provide support for a possible function of Myr1/Syh1 as a regulator sensing membrane composition along the vesicular pathways.

  • 5.
    Pisareva, Tatiana
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Kwon, Joseph
    Oh, Jihyun
    Kim, Young H.
    Ge, Changrong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Wieslander, Åke
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Choi, Jong-Soon
    Norling, Birgitta
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Model for Membrane Organization and Protein Sorting in the Cyanobacterium Synechocystis sp. PCC 6803 Inferred from Proteomics and Multivariate Sequence Analyses2011Inngår i: Journal of Proteome Research, ISSN 1535-3893, E-ISSN 1535-3907, Vol. 10, nr 8, s. 3617-3631Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cyanobacteria are unique eubacteria with an organized subcellular compartmentalization of highly differentiated internal thylakoid membranes (TM), in addition to the outer and plasma membranes (PM). This leads to a complicated system for transport and sorting of proteins into the different membranes and compartments. By shotgun and gel-based proteomics of plasma and thylakoid membranes from the cyanobacterium Synechocystis sp. PCC 6803, a large number of membrane proteins were identified. Proteins localized uniquely in each membrane were used as a platform describing a model for cellular membrane organization and protein intermembrane sorting and were analyzed by multivariate sequence analyses to trace potential differences in sequence properties important for insertion and sorting to the correct membrane. Sequence traits in the C-terminal region, but not in the N-terminal nor in any individual transmembrane segments, were discriminatory between the TM and PM classes. The results are consistent with a contact zone between plasma and thylakoid membranes, which may contain short-lived "hemifusion" protein traffic connection assemblies. Insertion of both integral and peripheral membrane proteins is suggested to occur through common translocons in these subdomains, followed by a potential translation arrest and structure-based sorting into the correct membrane compartment.

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