The amphoteric cartilage surface tested in the pH Range from 2.0 to 9.0

Background: Phospholipids adsorbed to negatively-charged proteoglycan matrix form phospholipid (membrane), have negatively charged surface (-PO4-) and are hydrophilic. Strong adsorption and strong cohesion are necessary for phospholipids to provide a good lubricant. The surface energy of spherical lipid bilayers have "bell-curve" shaped has amphoteric character and lowest surface energy at a pH 7.4 ± 1 of the natural joint. Objectives: The amphoteric character of the natural surface of the articular cartilage was determined by measuring the surface energy of the model spherical bilayer lipid membrane. It was found that the friction (f) vs. pH 2.0 to 9.0 of the pair (cartilage/cartilage) has the amphoteric character by exposing "bell-curve" shaped with an isoelectric point (IEP). Methods: The friction coefficient (f) was measured with the sliding pin-on-disc tribotester the friction between two surfaces (cartilage/cartilage) pair. The method of interfacial tension measurements of the spherical lipid bilayer model vs the pH over the range 0.2 to 9.0 was used. Results: The dependence of friction coefficient between two cartilage surfaces on the pH over the range 2.0 to 9.0 is demonstrated by a “bell - curve” in Fig. 2(A). The surface energy of a model spherical bilayer lipid membrane vs. the pH has the character of a “bell - curve” with an (IEP) is shown in Fig. 2(B). Conclusion: The amphoteric effect on friction between the bovine cartilage/cartilage contacts has been found to be highly sensitive to the pH of an aqueous solution. In this paper we demonstrate experimentally that the pH sensitivity of cartilage to friction provides a novel concept in joint lubrication on charged surfaces. The change in friction was consistently related to the change of charge density of an amphoteric surface.

De novo design of a nanopore for single-molecule detection that incorporates a β-hairpin peptide

The amino-acid sequence of a protein encodes information on its three-dimensional structure and specific functionality. De novo design has emerged as a method to manipulate the primary structure for the development of artificial proteins and peptides with desired functionality. This paper describes the de novo design of a pore-forming peptide, named SV28, that has a β-hairpin structure and assembles to form a stable nanopore in a bilayer lipid membrane. This large synthetic nanopore is an entirely artificial device for practical applications. The peptide forms multidispersely sized nanopore structures ranging from 1.7 to 6.3 nm in diameter and can detect DNAs. To form a monodispersely sized nanopore, we redesigned the SV28 by introducing a glycine-kink mutation. The resulting redesigned peptide forms a monodisperse pore with a diameter of 1.7 nm leading to detection of a single polypeptide chain. Such de novo design of a β-hairpin peptide has the potential to create artificial nanopores, which can be size adjusted to a target molecule.

A Ready-To-Use Metal-Supported Bilayer Lipid Membrane Biosensor for the Detection of Phenol in Water

This work presents a novel metal-supported bilayer lipid membrane (BLM) biosensor built on tyrosinase to quantitate phenol. The detection strategy is based on the enzyme–analyte initial association and not the commonly adopted monitoring of the redox cascade reactions; such an approach has not been proposed in the literature to date and offers many advantages for environmental monitoring with regard to sensitivity, selectivity, reliability and assay simplicity. The phenol sensor developed herein showed good analytical and operational characteristics: the detection limit (signal-to-noise ratio = 3) was 1.24 pg/mL and the sensitivity was 33.45 nA per pg/mL phenol concentration. The shelf life of the tyrosinase sensor was 12 h and the lifetime (in consecutive assays) was 8 h. The sensor was reversible with bathing at pH 8.5 and could be used for eight assay runs in consecutive assays. The validation in real water samples showed that the sensor could reliably detect 2.5 ppb phenol in tap and river water and 6.1 ppb phenol in lake water, without sample pretreatment. The prospects and applicability of the proposed biosensor and the underlying technology are also discussed.

Using wide biological pores to cap and contain the COVID-19 spike protein

Geometric analysis shows that the spike (S) protein in the COVID-19 virus (SARS-Cov-2) can fully or partially enter into the channel of a wide biological pore like perforin (PFN) or streptolysin (SLO) when the latter is anchored in a bilayer lipid membrane. The PFN channel is a β barrel formed from multiple monomers, for example a ~14 nm diameter channel is formed from 22 monomers. Coincidentally the wide canopy of S (which has three identical chains) has an enclosing diameter of ~14 nm. While inside the channel peripheral residues in the canopy may bind with residues on the pore side of the barrel. If there are no adverse cross-reactions this would effectively prevent S from interacting with a target cell. Calculations with data obtained from PDB and other sources show that there are ~12 peripheral residue triples in S within a circle of diameter ~14 nm that can potentially bind with 22 exposed residues in each barrel monomer. The revised Miyazawa-Jernighan matrix is used to calculate the binding energy of canopy-PFN barrel residue pairs. The results show a large number of binding pairs over distances of up to 38 Å into the pore. This geometric view of capture and containment points to the possibility of using biological pores to neutralize SARS-Cov-2 in its many variant forms. Some necessary conditions that must be satisfied for such neutralization to occur are noted. A wide pore (such as PFN or SLO) can also be used in an electrolytic cell to detect the presence of SARS-Cov-2, which would cause a large-sized blockade of the base current (the ionic current in a fully open pore). It can further be used to quantify the virus level in the sample. Solid-state pores, which have several advantages over biological ones, can be used instead; immune rejection is not an issue and there is no need for the spike or the virus to bind to the pore.

Using wide biological pores to cap and contain the COVID-19 spike protein

Geometric analysis shows that the spike (S) protein in the COVID-19 virus (SARS-Cov-2) can fully or partially enter into the channel of a wide biological pore like perforin (PFN) or streptolysin (SLO) when the latter is anchored in a bilayer lipid membrane. The PFN channel is a β barrel formed from multiple monomers, for example a ~14 nm diameter channel is formed from 22 monomers. Coincidentally the wide canopy of S (which has three identical chains) has an enclosing diameter of ~14 nm. While inside the channel peripheral residues in the canopy may bind with residues on the pore side of the barrel. If there are no adverse cross-reactions this would effectively prevent S from interacting with a target cell. Calculations with data obtained from PDB and other sources show that there are ~12 peripheral residue triples in S within a circle of diameter ~14 nm that can potentially bind with 22 exposed residues in each barrel monomer. The revised Miyazawa-Jernighan matrix is used to calculate the binding energy of canopy-PFN barrel residue pairs. The results show a large number of binding pairs over distances of up to 38 Å into the pore. This geometric view of capture and containment points to the possibility of using biological pores to neutralize SARS-Cov-2 in its many variant forms. Some necessary conditions that must be satisfied for such neutralization to occur are noted. A wide pore (such as PFN or SLO) can also be used in an electrolytic cell to detect the presence of SARS-Cov-2, which, by blocking the pore would cause a near total blockade of the base current (the ionic current in a fully open pore).

Using wide biological pores to cap and contain the COVID-19 spike protein

Geometric analysis shows that the spike (S) protein in the COVID-19 virus (SARS-Cov-2) can fully or partially enter into the channel of a wide biological pore like perforin (PFN) or streptolysin (SLO) when the latter is anchored in a bilayer lipid membrane. The PFN channel is a β barrel formed from multiple monomers, for example a ~14 nm diameter channel is formed from 22 monomers. Coincidentally the wide canopy of S (which has three identical chains) has an enclosing diameter of ~14 nm. While inside the channel peripheral residues in the canopy may bind with residues on the pore side of the barrel. If there are no adverse cross-reactions this would effectively prevent S from interacting with a target cell. Calculations with data obtained from PDB and other sources show that there are ~12 peripheral residue triples in S within a circle of diameter ~14 nm that can potentially bind with 22 exposed residues in each barrel monomer. The revised Miyazawa-Jernighan matrix is used to calculate the binding energy of canopy-PFN barrel residue pairs. The results show a large number of binding pairs over distances of up to 38 Å into the pore. This geometric view of capture and containment points to the possibility of using biological pores to neutralize SARS-Cov-2 in its many variant forms. Some necessary conditions that must be satisfied for such neutralization to occur are noted.

Potential Anti-Alzheimer Agents from Guanidinyl Tryptophan Derivatives with Activities of Membrane Adhesion and Conformational Transition Inhibitions

Guanidinyl tryptophan derivatives TGN1, TGN2, TGN3, and TGN4 were synthesized, and these compounds were shown to possess in vitro inhibitory activity for amyloid aggregation in a previous study. Nevertheless, the influence of the TGN series of compounds on the binding and permeation behaviors of an Aβ monomer to the cell membranes was not elucidated. In this study, we investigated the effect of compounds in the TGN series on the behavior of an Aβ monomer regarding its toxicity toward the bilayer lipid membrane using molecular dynamics (MD) simulation. MD simulations suggest that TGN4 is a potential agent that can interfere with the movement of the Aβ monomer into the membrane. The MM-GBSA result demonstrated that TGN4 exhibits the highest affinity to the Aβ1–42 monomer but has the lowest affinity to the bilayer. Moreover, TGN4 also contributes to a decrease in the binding affinity between the Aβ1–42 monomer and the POPC membrane. Regarding the results of the binding mode and conformational analyses, a high number of amino-acid residues were shown to provide the binding interactions between TGN4 and the Aβ1–42 monomer. TGN4 also reduces the conformational transition of the Aβ1–42 monomer by means of interacting with the monomer. The present study presents molecular-level insights into how the TGN series of compounds affect the membrane adsorption and the conformational transition of the Aβ1–42 monomer, which could be valuable for the further development of new anti-Alzheimer agents.