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  • 1.
    Ahlford, Katrin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Lind, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Adolfsson, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Rhodium-catalyzed asymmetric transfer hydrogenation of alkyl and aryl ketones in aqueous media2008Inngår i: Green Chemistry, ISSN 1463-9262, E-ISSN 1463-9270, Vol. 10, nr 8, s. 832-835Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel lipophilic rhodium catalyst was evaluated in the enantioselective transfer hydrogenation of ketones in water using sodium formate as the hydride donor, and in the presence of sodium docecylsulfonate. Alkyl alkyl ketones were reduced in good yields and in moderate to good enantioselectivities, and the reduction of aryl alkyl ketones proceeded with excellent enantioselectivity (up to 97% ee).

  • 2.
    Biverståhl, Henrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Lind, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Bodor, Andrea
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Biophysical studies of the membrane location of the voltage-gated sensors in the HsapBK and KvAP K(+) channels2009Inngår i: Biochimica et Biophysica Acta, ISSN 0006-3002, E-ISSN 1878-2434, Vol. 1788, nr 9, s. 1976-86Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The membrane location of two fragments in two different K(+)-channels, the KvAP (from Aeropyrum pernix) and the HsapBK (human) corresponding to the putative "paddle" domains, has been investigated by CD, fluorescence and NMR spectroscopy. Both domains interact with q = 0.5 phospholipid bicelles, DHPC micelles and with POPC vesicles. CD spectra demonstrate that both peptides become largely helical in the presence of phospholipid bicelles. Fluorescence quenching studies using soluble acrylamide or lipid-attached doxyl-groups show that the arginine-rich domains are located within the bilayered region in phospholipid bicelles. Nuclear magnetic relaxation parameters, T(1) and (13)C-(1)H NOE, for DMPC in DMPC/DHPC bicelles and for DHPC in micelles showed that the lipid acyl chains in the bicelles become less flexible in the presence of either of the fragments. An even more pronounced effect is seen on the glycerol carbons. (2)H NMR spectra of magnetically aligned bicelles showed that the peptide derived from KvAP had no or little effect on bilayer order, while the peptide derived from HsapBK had the effect of lowering the order of the bilayer. The present study demonstrates that the fragments derived from the full-length proteins interact with the bilayered interior of model membranes, and that they affect both the local mobility and lipid order of model membrane systems.

  • 3.
    Biverståhl, Henrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Lind, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Biophysical studies of the membrane location of the voltage-gated sensors in HsapBK and KvAPManuskript (Annet vitenskapelig)
  • 4.
    Haglund, Ellinor
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Öman, Tommy
    Department of chemistry, Umeå university.
    Lind, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Öhman, Anders
    Department of chemistry, Umeå university.
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Oliveberg, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    The HD-exchange motions of ribosomal protein S6 are insensitive to reversal of the protein-folding pathway.2009Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 1091-6490, Vol. 106, nr 51, s. 21619-21624Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An increasing number of protein structures are found to encompass multiple folding nuclei, allowing their structures to be formed by several competing pathways. A typical example is the ribosomal protein S6, which comprises two folding nuclei (sigma1 and sigma2) defining two competing pathways in the folding energy landscape: sigma1 --> sigma2 and sigma2 --> sigma1. The balance between the two pathways, and thus the order of folding events, is easily controlled by circular permutation. In this study, we make use of this ability to manipulate the folding pathway to demonstrate that the dynamic motions of the S6 structure are independent of how the protein folds. The HD-exchange protection factors remain the same upon complete reversal of the folding order. The phenomenon arises because the HD-exchange motions and the high-energy excitations controlling the folding pathway occur at separated free-energy levels: the Boltzmann distribution of unproductive unfolding attempts samples all unfolding channels in parallel, even those that end up in excessively high barriers. Accordingly, the findings provide a simple rationale for how to interpret native-state dynamics without the need to invoke fluctuations off the normal unfolding reaction coordinate.

  • 5. Jornvall, Hans
    et al.
    Lindahl, Emma
    Astorga-Wells, Juan
    Lind, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Holmlund, Anna
    Melles, Ermias
    Alvelius, Gunvor
    Nerelius, Charlotte
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Johansson, Jan
    Oligomerization and insulin interactions of proinsulin C-peptide: Threefold relationships to properties of insulin2010Inngår i: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, E-ISSN 1090-2104, Vol. 391, nr 3, s. 1561-1566Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Three principally different sites of action have been reported for proinsulin C-peptide, at surface-mediated, intracellular, and extracellular locations. Following up on the latter, we now find that (i) mass spectrometric analyses reveal the presence of the C-peptide monomer in apparent equilibrium with a low-yield set of oligomers in weakly acidic or basic aqueous solutions, even at low peptide concentrations (sub-mu M). It further shows not only C-peptide to interact with insulin oligomers (known before), but also the other way around. (ii) Polyacrylamide gel electrophoresis of C-peptide shows detectable oligomers upon Western blotting. Formation of thioflavin T positive material was also detected. (iii) Cleavage patterns of analogues are compatible with C-peptide as a substrate of insulin degrading enzyme. Combined, the results demonstrate three links with insulin properties, in a manner reminiscent of amyloidogenic peptides and their chaperons in other systems. If so, peripheral C-peptide/insulin interactions, absolute amounts of both peptides and their ratios may be relevant to consider in diabetic and associated diseases.

  • 6.
    Lind, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Biophysical studies of membrane associated peptides2009Doktoravhandling, med artikler (Annet vitenskapelig)
    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.

  • 7.
    Lind, Jesper
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Gräslund, Astrid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Membrane Interactions of Dynorphins2006Inngår i: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 45, s. 15931-15940Artikkel i tidsskrift (Fagfellevurdert)
  • 8.
    Lind, Jesper
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Lindahl, Emma
    Perálvarez-Marín, Alex
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Holmlund, Anna
    Jörnvall, Hans
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Structural features of proinsulin C-peptide oligomeric and amyloid states2010Inngår i: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 277, nr 18, s. 3759-68Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The formation and structure of proinsulin C-peptide oligomers has been investigated by PAGE, NMR spectroscopy and dynamic light scattering. The results obtained show that C-peptide forms oligomers of different sizes, and that their formation and size distribution is altered by salt and divalent metal ions, which indicates that the aggregation process is mediated by electrostatic interactions. It is further demonstrated that the size distribution of the C-peptide oligomers, in agreement with previous studies, is altered by insulin, which supports a physiologically relevant interaction between these two peptides. A small fraction of oligomers has previously been suggested to be in equilibrium with a dominant fraction of soluble monomers, and this pattern also is observed in the present study. The addition of modest amounts of sodium dodecyl sulphate at low pH increases the relative amount of oligomers, and this effect was used to investigate the details of both oligomer formation and structure by a combination of biophysical techniques. The structural properties of the SDS-induced oligomers, as obtained by thioflavin T fluorescence, CD spectroscopy and IR spectroscopy, demonstrate that soluble aggregates are predominantly in β-sheet conformation, and that the oligomerization process shows characteristic features of amyloid formation. The formation of large, insoluble, β-sheet amyloid-like structures will alter the equilibrium between monomeric C-peptide and oligomers. This leads to the conclusion that the oligomerization of C-peptide may be relevant also at low concentrations.

  • 9.
    Lind, Jesper
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Nordin, Jon
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Lipid dynamics in fast-tumbling bicelles with varying bilayer thickness: Effect of model transmembrane peptides2008Inngår i: Biochimica et Biophysica Acta, ISSN 0006-3002, E-ISSN 1878-2434, Vol. 1778, nr 11, s. 2526-2534Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The morphology of q=0.5 fast-tumbling bicelles prepared with three different acyl chain lengths has been investigated by NMR. It is shown that bicelles prepared with DLPC (12 C) and DHPC are on average larger than those containing DMPC or DPPC (14 and 16 C) and DHPC, which may be due to a higher degree of mixing between DLPC and DHPC. The fast internal mobility of the lipids was determined from natural abundance carbon-13 relaxation. A similar dynamical behaviour of the phospholipids in the three different bicelles was observed, although the DPPC lipid acyl chain displayed a somewhat lower degree of mobility, as evidenced by higher generalized order parameters throughout the acyl chain. Carbon-13 relaxation was also used to determine the effect of different model transmembrane peptides, with flanking Lys residues, on the lipid dynamics in the three different bicelles. All peptides had the effect of increasing the order parameters for the DLPC lipid, while no effect was observed on the longer lipid chains. This effect may be explained by a mismatch between the hydrophobic length of the peptides and the DLPC lipid acyl chain.

  • 10.
    Lind, Jesper
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Rämö, Tuulia
    Rosén Klement, Maria L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Bárány-Wallje, Elsa
    Epand, Richard M.
    Epand, Raquel F.
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Wieslander, Åke
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    High cationic charge and bilayer interface-binding helices in a regulatory lipid glycosyltransferase2007Inngår i: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 46, nr 19, s. 5664-5677Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 11.
    Madani, Fatemeh
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Lind, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Damberg, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Adams, Stephen
    Tsien, Roger
    Gräslund, Astrid O.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Hairpin Structure of a Biarsenical−Tetracysteine Motif Determined by NMR Spectroscopy2009Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, nr 13, s. 4613-4615Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The biarsenical−tetracysteine motif is a useful tag for genetic labeling of proteins with small molecules in living cells. The present study concerns the structure of a 12 amino acid peptide FLNCCPGCCMEP bound to the fluorophore ReAsH based on resorufin. 1H NMR spectroscopy was used to determine the solution structure of the complex formed between the peptide and the ReAsH moiety. Structure calculations based on the NMR results showed that the backbone structure of the peptide is fairly well defined, with a hairpinlike turn, similar to a type-II β-turn, formed by the central CPGC segment. The most stable complex was formed when As2 was bonded to C4 and C5 and As1 to C8 and C9. Two clear NOESY cross-peaks between the Phe1 side chain and ReAsH confirmed the close positioning of the phenyl ring of Phe1 and ReAsH. Phe1 was found to have an edge−face geometry relative to ReAsH. The close interaction between Phe1 and ReAsH may be highly significant for the fluorescence properties of the ReAsH complex.

  • 12.
    Szpryngiel, Scarlett
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Ge, Changrong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Lakovleva, Irina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Georgiev, Alexander
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Lind, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Wieslander, Åke
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Lipid Interacting Regions in Phosphate Stress Glycosyltransferase atDGD2 from Arabidopsis thaliana2011Inngår i: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 50, nr 21, s. 4451-4466Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Membrane lipid glycosyltransferases (GTs) in plants are enzymes that regulate the levels of the non-bilayer prone monogalactosyldiacylglycerol (GalDAG) and the bilayer-forming digalactosyldiacylglycerol (GalGalDAG). The relative amounts of these lipids affect membrane properties such as curvature and lateral stress. During phosphate shortage, phosphate is rescued by replacing phospholipids with GalGalDAG. The glycolsyltransferase enzyme in Arabidopsis thaliana responsible for this, atDGD2, senses the bilayer properties and interacts with the membrane in a monotopic manner. To understand the parameters that govern this interaction, we have identified several possible lipid-interacting sites in the protein and studied these by biophysical techniques. We have developed a multivariate discrimination algorithm that correctly predicts the regions in the protein that interact with lipids, and the interactions were confirmed by a variety of biophysical techniques. We show by bioinformatic methods and circular dichroism (CD), fluorescence, and NMR spectroscopic techniques that two regions are prone to interact with lipids in a surface-charge dependent way. Both of these regions contain Trp residues, but here charge appears to be the dominating feature governing the interaction. The sequence corresponding to residues 227–245 in the protein is seen to be able to adapt its structure according to the surface-charge density of a bilayer. All results indicate that this region interacts specifically with lipid molecules and that a second region in the protein, corresponding to residues 130–148, also interacts with the bilayer. On the basis of this, and sequence charge features in the immediate environment of S227–245, a response model for the interaction of atDGD2 with the membrane bilayer interface is proposed.

  • 13.
    Unnerståle, Sofia
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Lind, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Papadopoulos, Evangelos
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Solution structure of the HsapBK K+ channel voltage-sensor paddle sequence2009Inngår i: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 48, nr 25, s. 5813-5821Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Voltage-gated potassium channels open and close in response to changes in the membrane potential. In this study, we have determined the NMR solution structure of the putative S3b-S4 voltage-sensor paddle fragment, the part that moves to mediate voltage gating, of the HsapBK potassium channel in dodecylphosphocholine (DPC) micelles. This paper presents the first structure of the S3b-S4 fragment from a BK channel. Diffusion coefficients as determined from PFG NMR experiments showed that a well-defined complex between the peptide and DPC molecules was formed. The structure reveals a helix-turn-helix motif, which is in agreement with crystal structures of other voltage-gated potassium channels, thus indicating that it is feasible to study the isolated fragment. The paddle motifs generally contain several basic residues, implicated in the gating. The critical Arg residues in this structure all reside on the surface, which is in agreement with crystal structures of K(v) channels. Similarities in the structure of the S3b-S4 fragment in BK and K(v) channels as well as important differences are seen, which may be important for explaining the details in paddle movement within a bilayer.

  • 14.
    Ye, Weihua
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Lind, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik. Karolinska Institutet, Sweden.
    Eriksson, Jonny
    Mäler, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Characterization of the Morphology of Fast-Tumbling Bicelles with Varying Composition2014Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, nr 19, s. 5488-5496Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Small, fast-tumbling bicelles are frequently used in solution NMR studies of protein lipid interactions. For this purpose it is critical to have information about the organization of the lipids within the bicelle structure. We have studied the morphology of small, fast-tumbling bicelles containing DMPC and DHPC as a function of temperature, lipid concentration, and the relative ratio (q value) of lipid (DMPC) to detergent (DHPC) amounts. Dynamic light scattering and cryo-transmission electron microscopy techniques were used to measure the size of the bicelles and to monitor the shape and dispersity of the particles in the samples. The stability and size of DMPC-containing bicelle mixtures were found to be highly dependent on temperature and the total lipid concentration for mixtures with q = 1 and q = 1.5. Stable DMPC/DHPC bicelles are only formed at low q values (0.5). Bicelle mixtures with q > 0.5 appear to be multidisperse containing more than one component, one with r(H) around 2.5 nm and one with r(H) of 6-8 nm. This is interpreted as a coexistence of small (possibly mixed micelles) bicelles and much larger bicelles. Incubating the sample at 37 degrees C increases the phase separation. Moreover, low total amphiphile concentrations and low q values lead to the formation of a temperature-independent morphology, interpreted as the formation of small particles in which the DHPC and DMPC are more mixed. On the basis of these results, we propose the existence of a critical bicelle concentration, a parameter that determines the existence of bilayered bicelles, which varies with q value. This polymorphism was not observed at any concentrations for q = 0.5 bicelles, for which a small but detectable temperature dependence was observed at high concentrations. The results demonstrate that q = 0.5 mixtures predominantly form classical bicelles, but that caution is needed when using fast-tumbling mixtures with q values higher than 0.5.

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