2,125 research outputs found
The Third Dimension of Reading the Sugar Code by Lectins
Coding of biological information is not confined to nucleic acids and proteins. Endowed with the highest level of structural versatility among biomolecules, the glycan chains of cellular glycoconjugates are well-suited to generate molecular messages/signals in a minimum of space. The sequence and shape of oligosaccharides as well as spatial aspects of multivalent presentation are assumed to underlie the natural specificity/selectivity that cellular glycans have for endogenous lectins. In order to eventually unravel structure-activity profiles cyclic scaffolds have been used as platforms to produce glycoclusters and afford valuable tools. Using adhesion/growth-regulatory galectins and the pan-galectin ligand lactose as a model, emerging insights into the potential of cyclodextrins, cyclic peptides, calixarenes and glycophanes for this purpose are presented herein. The systematic testing of lectin panels with spatially defined ligand presentations can be considered as a biomimetic means to help clarify the mechanisms, which lead to the exquisite accuracy at which endogenous lectins select their physiological counterreceptors from the complexity of the cellular glycome
Microcavity supported lipid membranes: versatile platforms for building asymmetric lipid bilayers and for protein recognition
Microcavity supported lipid bilayers (MSLB) are contact-free membranes suspended across aqueousfilled
pores that maintain the lipid bilayer in a highly fluidic state and free from frictional interactions with substrate.
Such platforms offer the prospect of liposome-like fluidity with the compositional versatility and addressability of
supported lipid bilayers and thus offer significant opportunity for modelling membrane asymmetry, protein-membrane
interactions and aggregation at the membrane interface. Herein, we evaluate their performance by studying the effect
of transmembrane lipid asymmetry on lipid diffusivity, membrane viscosity and cholera toxin- ganglioside recognition
across six symmetric and asymmetric membranes including binary compositions containing both fluid and gel phase,
and ternary phase separated membrane compositions. Fluorescence lifetime correlation spectroscopy (FLCS) was used
to determine the lateral mobility of lipid and protein, and electrochemical impedance spectroscopy (EIS) enabled
detection of protein-membrane assembly over the nanomolar range. Transmembrane leaflet asymmetry was observed
to have profound impact on membrane electrochemical resistance where the resistance of a ternary symmetric phase
separated bilayer was found to be at least 2.6 times higher than the asymmetric bilayer with analogous composition at
the distal leaflet but where the lower leaflet comprised only 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC).
Similarly, the diffusion coefficient for MSLBs was observed to be 2.5 fold faster for asymmetric MSLBs where the lower
leaflet is DOPC alone. Our results demonstrate that interplay of lipid packing across both membrane leaflets and
concentration of GM1 both affect the extent of cholera toxin aggregation and consequent diffusion of the cholera-GM1
aggregates. Given that true biomembranes are both fluidic and asymmetric, MSLBs offer the opportunity for building
greater biomimicry into biophysical models and the approach described demonstrates the value of MSLBs in studying
aggregation and membrane associated multivalent interactions prevalent in many carbohydrates mediated processes
The host galaxies of strong CaII QSO absorption systems at z<0.5
We present new imaging and spectroscopic observations of the fields of five
QSOs with very strong intervening CaII absorption systems at redshifts z<0.5
selected from the Sloan Digital Sky Survey. Recent studies of these very rare
absorbers indicate that they may be related to damped Lyman alpha systems
(DLAs). In all five cases we identify a galaxy at the redshift of the CaII
system with impact parameters up to ~24 kpc. In four out of five cases the
galaxies are luminous (L ~L*), metal-rich (Z ~Zsun), massive (velocity
dispersion, sigma ~100 km/s) spirals. Their star formation rates, deduced from
Halpha emission, are high, in the range SFR = 0.3 - 30 Msun/yr. In our
analysis, we paid particular attention to correcting the observed emission line
fluxes for stellar absorption and dust extinction. We show that these effects
are important for a correct SFR estimate; their neglect in previous low-z
studies of DLA-selected galaxies has probably led to an underestimate of the
star formation activity in at least some DLA hosts. We discuss possible links
between CaII-selected galaxies and DLAs and outline future observations which
will help clarify the relationship between these different classes of QSO
absorbers.Comment: Accepted for publication in MNRAS, 14 pages, 9 figures. Version with
full resolution images available at
http://www.ast.cam.ac.uk/~bjz/papers/Zych_etal_2007a.pd
Lectins: getting familiar with translators of the sugar code
The view on the significance of the presence of glycans in glycoconjugates is undergoing a paradigmatic change. Initially mostly considered to be rather inert and passive, the concept of the sugar code identifies glycans as highly versatile platform to store information. Their chemical properties endow carbohydrates to form oligomers with unsurpassed structural variability. Owing to their capacity to engage in hydrogen (and coordination) bonding and C-H/Ï-interactions these "code words" can be "read" (in Latin, legere) by specific receptors. A distinct class of carbohydrate-binding proteins are the lectins. More than a dozen protein folds have developed carbohydrate-binding capacity in vertebrates. Taking galectins as an example, distinct expression patterns are traced. The availability of labeled endogenous lectins facilitates monitoring of tissue reactivity, extending the scope of lectin histochemistry beyond that which traditionally involved plant lectins. Presentation of glycan and its cognate lectin can be orchestrated, making a glycan-based effector pathway in growth control of tumor and activated T cells possible. In order to unravel the structural basis of lectin specificity for particular glycoconjugates mimetics of branched glycans and programmable models of cell surfaces are being developed by strategic combination of lectin research with synthetic and supramolecular chemistry
Inhibition of Burkholderia Multivorans Adhesion to Lung Epithelial Cells by Bivalent Lactosides
Burkholderia cepacia complex (Bcc) is an opportunistic pathogen in cystic fibrosis patients which is inherently resistant to antimicrobial agents. The mechanisms of attachment and pathogenesis of Bcc, a group of 17 species, are poorly understood. The most commonly identified Bcc species in newly colonised patients, Burkholderia multivorans, continues to be acquired from the environment. Development of therapies which can prevent or reduce the risk of colonization on exposure to Bcc in the environment would be a better alternative to antimicrobial agents. Previously, it has been shown that Bcc strains bound to many glycolipid receptors on lung epithelia. Using a real-time PCR method to quantify the levels of binding of B. multivorans to the lung epithelial cells, we have examined glycoconjugate derivatives for their potential to inhibit host cell attachment. Bivalent lactosides previously shown to inhibit galectin binding significantly reduced the attachment of B. multivorans to CF lung epithelial cells at micromolar concentrations. This was in contrast to monosaccharides and lactose, which were only effective in the millimolar range. Development of glycoconjugate therapies such as these, which inhibit attachment to lung epithelial cells, represent an alternative means of preventing infection with inherently antimicrobially resistant pathogens such as B. multivorans
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