Experimental Determination of van der Waals Energies in a Biological System

Van der Waals Exfoliation Processed Biopiezoelectric Submucosa Ultrathin Films

Piezoelectric biomaterials have attracted significant attention due to the potential effect of piezoelectricity on biological tissues and their versatile applications. However, the high cost and complexity of assembling and domain aligning biomolecules at a large scale, and the disordered arrangement of piezoelectric domains as well as the lack of ferroelectricity in natural biological tissues remain a roadblock toward practical applications. Here, utilizing the weak van der Waals interaction in the layered structure of small intestinal submucosa (SIS), a van der Waals exfoliation (vdWE) process is reported to fabricate ultrathin films down to the thickness of the effective piezoelectric domain. Based on that, the piezoelectric property is revealed of SIS stemming from the collagen fibril, with piezoelectric coefficients up to 4.1 pm V^-1 and in-plane polarization orientation parallel to the fibril axis. Furthermore, a biosensor based on the vdWE-processed SIS film with an in-plane electrode is demonstrated that produces open-circuit voltages of ≈250 mV under the cantilever vibration condition. The vdWE method shows great potential in facilely fabricating ultrathin films of soft tissues and biosensors.

Thermo-kinetic analysis space expansion for cyclophilin-ligand interactions - identification of a new nonpeptide inhibitor using Biacore™ T200

We have established a refined methodology for generating surface plasmon resonance sensor surfaces of recombinant his‐tagged human cyclophilin‐A. Our orientation‐specific stabilisation approach captures his‐tagged protein under ‘physiological conditions’ (150 mm NaCl, pH 7.5) and covalently stabilises it on Ni²⁺‐nitrilotriacetic acid surfaces, very briefly activated for primary amine‐coupling reactions, producing very stable and active surfaces (≥ 95% specific activity) of cyclophilin‐A. Variation in protein concentration with the same contact time allows straightforward generation of variable density surfaces, with essentially no loss of activity, making the protocol easily adaptable for studying numerous interactions; from very small fragments, ~ 100 Da, to large protein ligands. This new method results in an increased stability and activity of the immobilised protein and allowed us to expand the thermo‐kinetic analysis space, and to determine accurate and robust thermodynamic parameters for the cyclophilin‐A–cyclosporin‐A interaction. Furthermore, the increased sensitivity of the surface allowed identification of a new nonpeptide inhibitor of cyclophilin‐A, from a screen of a fragment library. This fragment, 2,3‐diaminopyridine, bound specifically with a mean affinity of 248 ± 60 μm. The X‐ray structure of this 109‐Da fragment bound in the active site of cyclophilin‐A was solved to a resolution of 1.25 Å (PDB: 5LUD), providing new insight into the molecular details for a potential new series of nonpeptide cyclophilin‐A inhibitors.

Correlating structure and energetics in protein-ligand interactions: paradigms and paradoxes

Predicting protein-binding affinities of small molecules, even closely related ones, is a formidable challenge in biomolecular recognition and medicinal chemistry. A thermodynamic approach to optimizing affinity in protein-ligand interactions requires knowledge and understanding of how altering the structure of a small molecule will be manifested in protein-binding enthalpy and entropy changes; however, there is a relative paucity of such detailed information. In this review, we examine two strategies commonly used to increase ligand potency. The first of these involves introducing a cyclic constraint to preorganize a small molecule in its biologically active conformation, and the second entails adding nonpolar groups to a molecule to increase the amount of hydrophobic surface that is buried upon binding. Both of these approaches are motivated by paradigms suggesting that protein-binding entropy changes should become more favorable, but paradoxes can emerge that defy conventional wisdom.

Structural and biochemical characterization of the cytosolic wheat cyclophilin TaCypA-1

Cyclophilins belong to a family of proteins that bind to the immunosuppressive drug cyclosporin A (CsA). Several members of this protein family catalyze the cis-trans isomerization of peptide bonds preceding prolyl residues. The present study describes the biochemical and structural characteristics of a cytosolic cyclophilin (TaCypA-1) cloned from wheat (Triticum aestivum L.). Purified TaCypA-1 expressed in Escherichia coli showed peptidyl-prolyl cis-trans isomerase activity, which was inhibited by CsA with an inhibition constant of 78.3 nM. The specific activity and catalytic efficiency (kcat/Km) of the purified TaCypA-1 were 99.06 ± 0.13 nmol s(-1) mg(-1) and 2.32 × 10(5) M(-1) s(-1), respectively. The structures of apo TaCypA-1 and the TaCypA-1-CsA complex were determined at 1.25 and 1.20 Å resolution, respectively, using X-ray diffraction. Binding of CsA to the active site of TaCypA-1 did not result in any significant conformational change in the apo TaCypA-1 structure. This is consistent with the crystal structure of the human cyclophilin D-CsA complex reported at 0.96 Å resolution. The TaCypA-1 structure revealed the presence of a divergent loop of seven amino acids (48)KSGKPLH(54) which is a characteristic feature of plant cyclophilins. This study is the first to elucidate the structure of an enzymatically active plant cyclophilin which shows peptidyl-prolyl cis-trans isomerase activity and the presence of a divergent loop.

Synaptic bistability due to nucleation and evaporation of receptor clusters

We introduce a bistability mechanism for long-term synaptic plasticity based on switching between two metastable states that contain significantly different numbers of synaptic receptors. One state is characterized by a two-dimensional gas of mobile interacting receptors and is stabilized against clustering by a high nucleation barrier. The other state contains a receptor gas in equilibrium with a large cluster of immobile receptors, which is stabilized by the turnover rate of receptors into and out of the synapse. Transitions between the two states can be initiated by either an increase (potentiation) or a decrease (depotentiation) of the net receptor flux into the synapse. This changes the saturation level of the receptor gas and triggers nucleation or evaporation of receptor clusters.

Streamlined, automated protocols for the production of milligram quantities of untagged recombinant human cyclophilin-A (hCypA) and untagged human proliferating cell nuclear antigen (hPCNA) using AKTAxpress

We developed streamlined, automated purification protocols for the production of milligram quantities of untagged recombinant human cyclophilin-A (hCypA) and untagged human proliferating cell nuclear antigen (hPCNA) from Escherichia coli, using the AKTAxpress chromatography system. The automated 2-step (cation exchange and size exclusion) purification protocol for untagged hCypA results in final purity and yields of 93% and approximately 5 mg L(-1) of original cell culture, respectively, in under 12h, including all primary sample processing and column equilibration steps. The novel automated 4-step (anion exchange, desalt, heparin-affinity and size exclusion, in linear sequence) purification protocol for untagged hPCNA results in final purity and yields of 87% and approximately 4 mg L(-1) of original cell culture, respectively, in under 24h, including all primary sample processing and column equilibration steps. This saves in excess of four full working days when compared to the traditional protocol, producing protein with similar final yield, purity and activity. Furthermore, it limits a time-dependent protein aggregation, a problem with the traditional protocol that results in a loss of final yield. Both automated protocols were developed to use generic commercially available pre-packed columns and automatically prepared minimal buffers, designed to eliminate user and system variations, maximize run reproducibility, standardize yield and purity between batches, increase throughput and reduce user input to a minimum. Both protocols represent robust generic methods for the automated production of untagged hCypA and hPCNA.