Localized production of human E-cadherin-derived first repeat in Escherichia coli

Probing the interaction between cHAVc3 peptide and the EC1 domain of E-cadherin using NMR and molecular dynamics simulations

The goal of this work is to probe the interaction between cyclic cHAVc3 peptide and the EC1 domain of human E-cadherin protein. Cyclic cHAVc3 peptide (cyclo(1,6)Ac-CSHAVC-NH₂) binds to the EC1 domain as shown by chemical shift perturbations in the 2D ¹H,-¹⁵N-HSQC NMR spectrum. The molecular dynamics (MD) simulations of the EC1 domain showed folding of the C-terminal tail region into the main head region of the EC1 domain. For cHAVc3 peptide, replica exchange molecular dynamics (REMD) simulations generated five structural clusters of cHAVc3 peptide. Representative structures of cHAVc3 and the EC1 structure from MD simulations were used in molecular docking experiments with NMR constraints to determine the binding site of the peptide on EC1. The results suggest that cHAVc3 binds to EC1 around residues Y36, S37, I38, I53, F77, S78, H79, and I94. The dissociation constants (K_d values) of cHAVc3 peptide to EC1 were estimated using the NMR chemical shifts data and the estimated K_ds are in the range of .5 × 10^-5-7.0 × 10^-5 M.

(1)H, (13)C and (15)N backbone assignment of the EC-1 domain of human E-cadherin

The Extracellular 1 (EC1) domain of E-cadherin has been shown to be important for cadherin-cadherin homophilic interactions. Cadherins are responsible for calcium-mediated cell-cell adhesion located at the adherens junction of the biological barriers (i.e., intestinal mucosa and the blood-brain barrier (BBB)). Cadherin peptides can modulate cadherin interactions to improve drug delivery through the BBB. However, the mechanism of modulating the E-cadherin interactions by cadherin peptides has not been fully elucidated. To provide a basis for subsequent examination of the structure and peptide-binding properties of the EC1 domain of human E-cadherin using solution NMR spectroscopy, the (1)H, (13)C and (15)N backbone resonance of the uniformly labeled-EC1 were assigned and the secondary structure was determined based on the chemical shift values. These resonance assignments are essential for assessing protein-ligand interactions and are reported here.

Improving the stability of the EC1 domain of E-cadherin by thiol alkylation of the cysteine residue

The objective of this work was to improve chemical and physical stability of the EC1 protein derived from the extracellular domain of E-cadherin. In solution, the EC1 protein has been shown to form a covalent dimer via a disulfide bond formation followed by physical aggregation and precipitation. To improve solution stability of the EC1 protein, the thiol group of the Cys13 residue in EC1 was alkylated with iodoacetate, iodoacetamide, and maleimide-PEG-5000 to produce thioether derivatives called EC1-IA, EC1-IN, and EC1-PEG. The physical and chemical stabilities of the EC1 derivatives and the parent EC1 were evaluated at various pHs (3.0, 7.0, and 9.0) and temperatures (0, 3, 70 °C). The structural characteristics of each molecule were analyzed by circular dichroism (CD) and fluorescence spectroscopy and the derivatives have similar secondary structure as the parent EC1 protein at pH 7.0. Both EC1-IN and EC1-PEG derivatives showed better chemical and physical stability profiles than did the parent EC1 at pH 7.0. EC1-PEG had the best stability profile compared to EC1-IN and EC1 in solution under various conditions.

The role of covalent dimerization on the physical and chemical stability of the EC1 domain of human E-cadherin

The objective of this work was to evaluate the solution stability of the EC1 domain of E-cadherin under various conditions. The EC1 domain was incubated at various temperatures (4, 37, and 70 degrees C) and pH values (3.0, 7.0, and 9.0). At pH 9.0 and 37 or 70 degrees C, a significant loss of EC1 was observed due to precipitation and a hydrolysis reaction. The degradation was suppressed upon addition of dithiothreitol (DTT), suggesting that the formation of EC1 dimer facilitated the EC1 degradation. At 4 degrees C and various pH values, the EC1 secondary and tertiary showed changes upon incubation up to 28 days, and DTT prevented any structural changes upon 28 days of incubation. Molecular dynamics simulations indicated that the dimer of EC1 has higher mobility than does the monomer; this higher mobility of the EC1 dimer may contribute to instability of the EC1 domain.

Single-molecule analysis of cadherin-mediated cell-cell adhesion

Cadherins are ubiquitous cell surface molecules that are expressed in virtually all solid tissues and localize at sites of cell-cell contact. Cadherins form a large and diverse family of adhesion molecules, which play a crucial role in a multitude of cellular processes, including cell-cell adhesion, motility, and cell sorting in maturing organs and tissues, presumably because of their different binding capacity and specificity. Here, we develop a method that probes the biochemical and biophysical properties of the binding interactions between cadherins expressed on the surface of living cells, at the single-molecule level. Single-molecule force spectroscopy reveals that classical cadherins, N-cadherin and E-cadherin, form bonds that display adhesion specificity, and a pronounced difference in adhesion force and reactive compliance, but not in bond lifetime. Moreover, their potentials of interaction, derived from force-spectroscopy measurements, are qualitatively different when comparing the single-barrier energy potential for the dissociation of an N-cadherin-N-cadherin bond with the double-barrier energy potential for an E-cadherin-E-cadherin bond. Together these results suggest that N-cadherin and E-cadherin molecules form homophilic bonds between juxtaposed cells that have significantly different kinetic and micromechanical properties.

Expression, purification, and structural study of the EC4 domain of E-cadherin

The objective of this work was to produce unlabeled and 15N-labeled EC4 domain protein from E-cadherin for studying its structure and binding properties to other EC domains as well as to E-cadherin peptides. The EC4 domain of E-cadherin was expressed in Escherichia coli from the vector pASK-IBA6 and localized in the periplasmic space of E. coli. This protein contains a Streptag sequence at the N-terminus, and thus was purified using a Strep-Tactin affinity column. However, at high concentrations the 15N-labeled EC4 protein showed an unstable conformation. Conditions for stabilizing the conformation of this protein were evaluated using CD spectroscopy. The CD results showed that this protein has high conformational stability in Tris buffer at pH 6.0 in the presence of 10 mM calcium chloride.