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High cationic charge and bilayer interface-binding helices in a regulatory lipid glycosyltransferase
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
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2007 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 46, no 19, 5664-5677 p.Article in journal (Refereed) Published
Abstract [en]

In the prokaryote Acholeplasma laidlawii, membrane bilayer properties are sensed and regulated by two interface glycosyltransferases (GTs), synthesizing major nonbilayer- (alMGS GT) and bilayer-prone glucolipids. These enzymes are of similar structure, as many soluble GTs, but are sensitive to lipid charge and curvature stress properties. Multivariate and bioinformatic sequence analyses show that such interface enzymes, in relation to soluble ones of similar fold, are characterized by high cationic charge, certain distances between small and cationic amino acids, and by amphipathic helices. Varying surface contents of Lys/Arg pairs and Trp indicate different membrane-binding subclasses. A predicted potential (cationic) binding helix from alMGS was structurally verified by solution NMR and CD. The helix conformation was induced by a zwitterionic as well as anionic lipid environment, and the peptide was confined to the bilayer interface. Bilayer affinity of the peptide, analyzed by surface plasmon resonance, was higher than that for soluble membrane-seeking proteins/peptides and rose with anionic lipid content. Interface intercalation was supported by phase equilibria in membrane lipid mixtures, analyzed by 31P NMR and DSC. An analogous, potentially binding helix has a similar location in the structurally determined Escherichia coli cell wall precursor GT MurG. These two helices have little sequence conservation in alMGS and MurG homologues but maintain their amphipathic character. The evolutionary modification of the alMGS binding helix and its location close to the acceptor substrate site imply a functional importance in enzyme catalysis, potentially providing a mechanism by which glycolipid synthesis will be sensitive to membrane surface charge and intrinsic curvature strain.

Place, publisher, year, edition, pages
2007. Vol. 46, no 19, 5664-5677 p.
Identifiers
URN: urn:nbn:se:su:diva-24460DOI: 10.1021/bi700042xISI: 000246283600005OAI: oai:DiVA.org:su-24460DiVA: diva2:197566
Note
Part of urn:nbn:se:su:diva-7056Available from: 2007-09-13 Created: 2007-09-04 Last updated: 2017-12-13Bibliographically approved
In thesis
1. The advantages of being small: Glycosyltransferases in many dimensions and glycolipid synthesis in Mycoplasma Pneumoniae
Open this publication in new window or tab >>The advantages of being small: Glycosyltransferases in many dimensions and glycolipid synthesis in Mycoplasma Pneumoniae
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The synthesis and breakdown of sugars is one of the most important functions in Nature. Consequently, sugar structures are used both as energy storage and as building blocks to stabilise and protect the cell. The formation of these structures is performed by glycosyltransferases (GT), an enzyme group structurally conserved within all kingdoms. Until now, only two different folds have been discovered by crystallisation of GTs, i.e. GT-A and GT-B. A third fold family has however been proposed by fold predictions. In this thesis, a multivariate data analysis was successfully used in classifying and predicting both fold and reaction mechanism (inverting or retaining) of GTs. This method was also used to obtain information about the separating parameters for the reaction mechanism classification. This information could be traced back to the amino acid sequence. The method could as well be used to analyse and identify the properties of membrane binding regions of GTs, and subsequently distinguish soluble from membrane-associated enzymes. Most functionally characterised enzymes only use one substrate, synthesising one product. Mycoplasma pneumoniae, a common human pathogen with a small genome has only three proposed GTs. The bacterium was, however expected to have a greater number of GTs, due to its ability to make both glycolipids and capsule. Here we have determined the function of one of these enzymes, MPN483 and discovered its ability to both use different acceptors, and make elongated glycolipids with up to three galactose residues, with both DAG and ceramide as the base. Many of the synthesised glycolipids were also found to be immunogenic, hence showing their biological importance. The properties of lipids are known to be important for the function of a biological membrane. We have here shown that not only the charge but also the shape of the lipids are important for several protein mediated membrane processes in Echerichia coli, such as the function of the LacY.

Place, publisher, year, edition, pages
Stockholm: Institutionen för biokemi och biofysik, 2007. 56 p.
Keyword
Glycosyltransferase, lipid, membrane, glycolipid, ACC, PLS-DA
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-7056 (URN)978-91-7155-503-8 (ISBN)
Public defence
2007-10-05, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 10:00
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Supervisors
Available from: 2007-09-13 Created: 2007-09-04Bibliographically approved
2. Biophysical studies of membrane associated peptides
Open this publication in new window or tab >>Biophysical studies of membrane associated peptides
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A large part of the processes in living organisms involves proteins acting in a biological membrane. Biophysical studies on isolated model systems can give important understandings of the complicated biological mechanisms in the membrane. In this thesis peptide membrane interaction mechanisms are studied in several different systems. The membrane interactions of the unstructured endogenous opioid peptides dynorphinA (DynA) and dynorphinB (DynB) were investigated with Saturation Transfer Difference (STD) experiments, supplemented by various other NMR methods. The combined results support a conclusion that DynA binds to the lipid bilayer with the N-terminal residues inserted into the hydrophobic region and the C-terminal residues more loosely attached to the surface, while DynB is situated parallel to the bilayer. This difference in membrane interaction can explain observations that DynA has membrane perturbing effects while DynB has not. In the second study the binding domain of the glycosyltransferase A.laidlawii Monoglycosyldiacyl Glycerol Synthase (alMGS) was predicted and investigated mainly with NMR which enabled the determination of the 3D structure and position in a lipid environment. The phospholipid bilayers induce a large amphipathic α-helical content in the peptide, which aligns parallel but slightly tilted along the lipid surface with the N-terminus situated closer to the hydrophobic region. Lipid perturbation effects caused by peptide-membrane interactions were investigated by studying the influence of model transmembrane peptides on lipid dynamics in phospholipid bicelles with varying bilayer thickness. 13C-relaxation NMR of the lipids was used to survey the effects of the model peptides on the lipid bilayer.In paper IV and V structure and membrane interaction properties of the highly charged and flexible helix-turn-helix motif named the 'voltage sensor paddle' from two transmebrane voltage gated potassium channels was investigated. In membrane mimetic media, the KvaP paddle adopts the same type of helix-turn-helix conformation which can be seen in the Xray structure of the entire ion channel. The membrane interaction of the paddle HsapBK was compared with the corresponding one in KvaP, and both were inserted in the lipid bilayer but perturbed the lipid system differently, which may indicate differences in their function. Paper VI treats the structure of the novel site-specific fluorophore ReAsH bound to an optimized peptide sequence. The analysis shows that the important peptide mid segment configuration of CCPGCC is optimal for the ReAsH binding and that the N-terminal Phe1 plays an important role for the fluorophore process.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2009. 55 p.
Keyword
NMR, spectroscopy, membrane interaction, bicelles
National Category
Chemical Sciences
Research subject
Biophysics
Identifiers
urn:nbn:se:su:diva-27488 (URN)978-91-7155-888-6 (ISBN)
Public defence
2009-06-04, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2009-05-14 Created: 2009-05-05 Last updated: 2012-08-28Bibliographically approved

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