LRP6 dimerization through its LDLR domain is required for robust canonical Wnt pathway activation

Canonical Wnt/β-catenin signaling pathway plays important roles in multiple aspects of cellular responses in development and diseases. It is currently thought that Wnt receptor Frizzled (Frz) exists separately to Wnt coreceptors LRP5 and LRP6 (LRP5/6), and that Wnt-Frz-LRP5/6 triple complex formation bridged by Wnt ligand is needed for canonical pathway activation. We recently showed that Frz and LRP5/6 interact with each other in the absence of Wnt ligand binding and this interaction maintains the Frz-LRP5/6 complex in an inactive state. Here, we further show that Wnt ligand stimulation induces conformational change of the Frz-LRP6 complex and leads to hexamer formation containing the core LDLR domain-mediated LRP6 homodimer that is stabilized by two pairs of Wnt3a and Frz8, that is, Wnt3a-Frz8-LRP6-LRP6-Frz8-Wnt3a. This LDLR-mediated LRP6 dimerization is essential for robust canonical Wnt pathway activation. Our study thus suggests a previously unrecognized mode of receptor interaction in Wnt signal initiation.

NBO, NMR, UV, FT-IR, FT-Raman spectra and molecular structure (monomeric and dimeric structures) investigation of 4-Chloro-3,5-Xylenol: a combined experimental and theoretical study

In this work, a joint experimental (FTIR and FT-Raman) and theoretical (DFT and ab initio) study on the structure and the vibrations of 4-Chloro-3,5-Xylenol (CXL) are compared and analyzed. CXL is a chlorinated phenolic antiseptic which is a bactericide against most gram-positive bacteria. The first hyperpolarizability (β0) of this novel molecular system and related non-linear properties of CXL are calculated using HF/6-311++G(d,p) method on the finite-field approach. The energy and oscillator strength calculated using absorption spectra (UV-Vis spectrum), this spectral analysis confirms the charge transfer of the molecule. The theoretical (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by Gauge Including Atomic Orbital (GIAO) method, to analyze the molecular environment as well as the delocalization activities of electron clouds. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (χ), chemical hardness (η), first electron excitation energy (τ) and electrophilicity index (ω) as well as local reactivity (S) analyzed using HOMO and LUMO energies; the energy band gap are also determined. NBO analysis shows that charge in electron density(ED) in the σ(*) and π(*) antibonding orbitals and E((2)) energies confirms the occurrence of ICT (Intramolecular Charge Transfer) within the molecule. Inter molecular hydrogen bonds exist between -OH group, give the evidence for the formation of dimer entities in the title molecule. The influences of chlorine atom, hydroxyl group and methyl group on the geometry of benzene and its normal modes of vibrations (monomer and dimer of CXL) have also been discussed. Finally the calculated results were applied to simulate Infrared and Raman spectra of the title molecule which show good agreement with observed spectra.

Isolation of a new human scFv antibody recognizing a cell surface binding site to CEACAM1. Large yield production, purification and characterization in E. coli expression system

The CEACAM1 cell adhesion molecule has recently received considerable interest as a tumour target antigen since its re-expression often occurs in the advanced stages of multiple malignancies including malignant melanoma, non-small cell lung cancer and other types of solid tumors. In this study, we describe the expression-purification and characterization of the new single chain variable fragment (scFv) antibody named DIATHIS1, that recognizes the N-terminal IgV-like domain present in CEACAM1. Three validation batches show that the production process is robust and reproducible. The scFv DIATHIS1 is formulated as a naturally occurring mixture of monomer and dimer. The antibody is biophysically stable at low temperature (-80°C), different concentrations and remains biologically active for at least 24months. The thermal stability of scFv DIATHIS1 at 37°C shows important features for its activity in vivo. The dimer behaves as a reservoir converting slowly into monomer. The monomer and dimer forms of scFv DIATHIS1 were isolated and characterized, showing high reactivity for CEACAM1. This new composition of antibody could have advantageous pharmacokinetics parameters over conventional scFv for in vivo applications.

Structure, vibrational spectra and DFT characterization of the intra- and inter-molecular interactions in 2-hydroxy-5-methylpyridine-3-carboxylic acid--normal modes of the eight-membered HB ring

Fourier transform IR and Raman spectra, XRD studies and DFT quantum chemical calculations have been used to characterize the structural and vibrational properties of 2-hydroxy-5-methylpyridine-3-carboxylic acid. In the unit-cell of this compound two molecules related by the inversion center interact via OH⋯N hydrogen bonds. The double hydrogen bridge system is spaced parallel to the (102) crystallographic plane forming eight-membered arrangement characteristic for pyridine derivatives. The six-membered ring is the second characteristic unit formed via the intramolecular OH⋯O hydrogen bond. The geometry optimization of the monomer and dimer have been performed applying the Gaussian03 program package. All calculations were performed in the B3LYP/6-31G(d,p) basis set using the XRD data as input parameters. The relation between the molecular and crystal structures has been discussed in terms of the hydrogen bonds formed in the unit cell. The vibrations of the dimer have been discussed in terms of the resonance inside the system built of five rings coupled via hydrogen bonds.

Biochemical and preliminary X-ray characterization of the tumor-associated calcium signal transducer 2 (Trop2) ectodomain

Trop2 is a stem/progenitor cell marker, which is also upregulated in several human carcinomas. The largest part of the molecule, recognized by several monoclonal antibodies, is represented by the extracellular part (ectodomain) and is composed of three modules. The aim of our work was to prepare the ectodomain of Trop2 in quantities sufficient for structural and functional studies. We used the Spodoptera frugiperda (Sf9) insect cell expression system to prepare the Trop2 ectodomain (Trop2EC) in two forms - wt glycosylated (gTrop2EC) and mutant non-glycosylated form (Trop2EC(Δ/N)). Recombinant protein was purified from cell culture supernatants using two subsequent nickel ion-affinity chromatographies with a final yield of 15-17mg of purified recombinant protein per liter of culture. Size-exclusion chromatography together with MALS and chemical crosslinking were used to demonstrate for the first time that the Trop2 ectodomain forms a dimer. Both gTrop2EC and Trop2EC(Δ/N) exhibit similar biochemical properties, however the solubility of Trop2EC(Δ/N) is much lower (less than 1mg/ml). For the purpose of structural studies, we crystallized the glycosylated form gTrop2EC. The native dataset was collected with a resolution of 2.94Å and will be used in ongoing work for phasing and structure solution to further understand the role of Trop2 and the structure-function relation between Trop2 and the epithelial cell adhesion molecule (EpCAM).

Single-molecule imaging of receptor-receptor interactions

Single-molecule imaging is a powerful tool for the study of dynamic molecular interactions in living cell plasma membranes. Herein, we describe a single-molecule imaging microscopy technique that can be used to measure lifetimes and densities of receptor dimers and oligomers. This method can be performed using a total internal reflection fluorescent microscope equipped with one or two high-sensitivity cameras. For dual-color observation, two images obtained synchronously in different colors are spatially corrected and then overlaid. Receptors must be expressed at low density in cell plasma membranes because high-density expression (>2 molecules/μm(2)) creates difficulty for tracking individual fluorescent spots. In addition, the receptors should be labeled with highly photostable fluorophores at high efficiency because short photobleaching lifetimes and low labeling efficiency of receptors reduce the probability of detecting dimers and oligomers. In this chapter, we describe methods for observing and detecting colocalization of the individual fluorescent spots of receptors labeled with fluorophores via small tags and the estimation of true dimer and oligomer lifetimes after correction with photobleaching lifetimes of fluorophores.

G protein-coupled receptor transactivation: from molecules to mice

G protein-coupled receptors (GPCRs) mediate a diverse range of physiological functions via activation of complex signaling systems. Organization of GPCRs in to dimers and oligomers provides a mechanism for both signal diversity and specificity in cellular responses, yet our understanding of the physiological significance of dimerization, particularly homodimerization, has not been forthcoming. This chapter will describe how we have investigated the physiological importance of GPCR homodimerization, using the luteinizing hormone/chorionic gonadotropin receptor as a model GPCR. Using transactivation as a mode of assessing receptor dimerization, we describe our cellular system and functional assays for assessment of transactivation in vitro and detail our strategy for generating a mouse model to assess GPCR transactivation in vivo.

Contributions of fluorescence techniques to understanding G protein-coupled receptor dimerisation

G protein-coupled receptors (GPCRs) are the largest class of eukaryotic cell-surface receptors and, over the last decade, it has become clear that they are capable of dimerisation. Whilst many biochemical and biophysical approaches have been used to study dimerisation, fluorescence techniques, including Förster resonance energy transfer and single molecule fluorescence, have been key players. Here we review recent contributions of fluorescence techniques to investigate GPCR dimers, including dimerisation in cell membranes and native tissues, the effect of ligand binding on dimerisation and the kinetics of dimer formation and dissociation. The challenges of studying multicomponent membrane protein systems have led to the development and refinement of many fluorescence assays, allowing the functional consequences of receptor dimerisation to be investigated and individual protein molecules to be imaged in the membranes of living cells. It is likely that the fluorescence techniques described here will be of use for investigating many other multicomponent membrane protein systems.

Intermolecular Interactions of Chrysanthemum virus B Coat Protein: Implications for Capsid Assembly

Chrysanthemum virus B coat protein constitutes the viral capsid which, besides other functions, encapsulates and protects the viral nucleic acid. We have demonstrated homotypic interaction of the coat protein subunits, essentially important for dimer formation, which is the first step during capsid assembly in vivo and in vitro. Interaction capacity of full length and truncated protein has been investigated and important regions have been identified through protein-protein interaction in yeast and by co-immunoprecipitation assays. Complete coat protein was found to interact strongly with similar subunits. Constructs with 102 amino acids from the N-terminal and 64 amino acids from C-terminal were found to be inconsequential for dimer formation as they did not show any interaction with similar subunits or with full length protein when analysed for β-galactosidase or histidine prototrophy. Results suggest that the region of 98-184 amino acids from the middle plays an important role in the process, probably without the involvement of N- and C- terminals.