Force-Induced Selective Dissociation of Noncovalent Antibody–Antigen Bonds

Advances in the Biological Application of Force-Induced Remnant Magnetization Spectroscopy

Biomolecules participate in various physiological and pathological processes through intermolecular interactions generally driven by non-covalent forces. In the present review, the force-induced remnant magnetization spectroscopy (FIRMS) is described and illustrated as a novel method to measure non-covalent forces. During the FIRMS measurement, the molecular magnetic probes are magnetized to produce an overall magnetization signal. The dissociation under the interference of external force yields a decrease in the magnetic signal, which is recorded and collected by atomic magnetometer in a spectrum to study the biological interactions. Furthermore, the recent FIRMS development with various external mechanical forces and magnetic probes is summarized.

Refreshable Nanobiosensor Based on Organosilica Encapsulation of Biorecognition Elements

Implantable and wearable biosensors that enable monitoring of biophysical and biochemical parameters over long durations are highly attractive for early and presymptomatic diagnosis of pathological conditions and timely clinical intervention. Poor stability of antibodies used as biorecognition elements and the lack of effective methods to refresh the biosensors upon demand without severely compromising the functionality of the biosensor remain significant challenges in realizing protein biosensors for long-term monitoring. Here, we introduce a novel method involving organosilica encapsulation of antibodies for preserving their biorecognition capability under harsh conditions, typically encountered during the sensor refreshing process, and elevated temperature. Specifically, a simple aqueous rinsing step using sodium dodecyl sulfate (SDS) solution refreshes the biosensor by dissociating the antibody-antigen interactions. Encapsulation of the antibodies with an organosilica layer is shown to preserve the biorecognition capability of otherwise unstable antibodies during the SDS treatment, thus ultimately facilitating the refreshability of the biosensor over multiple cycles. Harnessing this method, we demonstrate the refreshability of plasmonic biosensors for anti-IgG (model bioanalyte) and neutrophil gelatinase-associated lipocalin (NGAL) (a biomarker for acute and chronic kidney injury). The novel encapsulation approach demonstrated can be easily extended to other transduction platforms to realize refreshable biosensors for monitoring of protein biomarkers over long durations.

Nanoprobe-based force spectroscopy as a versatile platform for probing the mechanical adhesion of bacteria

The first stage of biofilm-associated infections is commonly caused by initial adhesion of bacteria to intravascular tubes, catheters and other medical devices. The overuse of antibiotics to treat these infections has led to the spread of antibiotic resistance, which has made infections difficult to eradicate. It is crucial to develop advanced strategies to inhibit biofilm formation, avoiding the emergence of antibiotic resistance. Previously, it has been reported that substrate stiffness plays an important role in the initial attachment of bacteria. However, the mechanism of how the stiffness modulates the initial adhesion of bacteria remains unclear. Here, we developed magnetic nanoprobe-based force-induced remnant magnetization spectroscopy (FIRMS) as a new platform to measure the adhesion force of bacteria. Through examining the initial adhesion force and the adhesive protein, fibronectin-binding protein (FnBP), of Staphylococcus aureus (S. aureus), we found that the increase of the substrate stiffness promoted the expression of FnBP, thus enhancing the initial adhesion force of bacteria. Following the formation of initial adhesion, the substrates with soft stiffness delayed the biofilm formation, whereas those with moderate stiffness showed preferential promotion of the biofilm formation. We expect this versatile platform to be beneficial to the study of adhesion behaviors of bacteria that sheds light on the design of new medical materials to treat microbial infections.

Insulin-like growth factor type I selectively binds to G-quadruplex structures

BACKGROUND

G-quadruplex has been viewed as a promising therapeutic target in oncology due to its potentially important roles in physiological and pathological processes. Emerging evidence suggests that the biological functions of G-quadruplexes are closely related to the binding of some proteins. Insulin-like growth factor type I (IGF-1), as a significant modulator of cell growth and development, may serve as a quadruplex-binding protein.

METHODS

The binding affinity and selectivity of IGF-1 to different DNA motifs in solution were measured by using fluorescence spectroscopy, Surface Plasmon Resonance (SPR), and force-induced remnant magnetization (FIRM). The effects of IGF-1 on the formation and stability of G-quadruplex structures were evaluated by circular dichroism (CD) and melting fluorescence resonance energy transfer (FRET) spectroscopy. The influence of quadruplex-specific ligands on the binding of G-quadruplexes with IGF-1 was determined by FIRM.

RESULTS

IGF-1 shows a binding specificity for G-quadruplex structures, especially the G-quadruplex structure with a parallel topology. The quadruplex-specific ligands TMPyP4 and PDS (Pyridostatin) can inhibit the interaction between G-quadruplexes and proteins.

CONCLUSIONS

IGF-1 is demonstrated to selectively bind with G-quadruplex structures. The use of quadruplex-interactive ligands could modulate the binding of IGF-1 to G-quadruplexes.

GENERAL SIGNIFICANCE

This study provides us with a new perspective to understand the possible physiological relationship between IGF-1 and G-quadruplexes and also conveys a strategy to regulate the interaction between G-quadruplex DNA and proteins.

Nanopurpurin-based photodynamic therapy destructs extracellular matrix against intractable tumor metastasis

Nanomaterials-based photodynamic therapy (PDT) has been used to treat malignant cells. However, the intrinsic impact of nanomaterials-based PDT on mechanical properties of intractable tumor cells is not well understood. Herein, we demonstrated that the mechanical forces of Taxol-resistant tumor cells were decreased by nanopurpurin-based PDT destructing extracellular matrix (ECM), increasing therapy sensitivity and repressing tumor metastasis. Combining FIRMS and general confocal microscope, we observed that the disruption of ECM by photodynamic reaction of P18-nanoconfined liposome (P18⊂L) induced a decrease of adhesion force and biomechanical properties of Taxol-resistant cells through the attenuation of actomyosin-based contractility thereby inhibiting cell migration and metastasis in vivo. Moreover, the destroyed ECM by P18⊂L PDT increased the therapy sensitivity. A clearer understanding of the effect of nanopurpurin-based PDT on mechanical properties and behaviors of intractable tumor cells will provide new and important basis for developing new therapeutic strategies.

Biosensing Using Magnetic Particle Detection Techniques

Magnetic particles are widely used as signal labels in a variety of biological sensing applications, such as molecular detection and related strategies that rely on ligand-receptor binding. In this review, we explore the fundamental concepts involved in designing magnetic particles for biosensing applications and the techniques used to detect them. First, we briefly describe the magnetic properties that are important for bio-sensing applications and highlight the associated key parameters (such as the starting materials, size, functionalization methods, and bio-conjugation strategies). Subsequently, we focus on magnetic sensing applications that utilize several types of magnetic detection techniques: spintronic sensors, nuclear magnetic resonance (NMR) sensors, superconducting quantum interference devices (SQUIDs), sensors based on the atomic magnetometer (AM), and others. From the studies reported, we note that the size of the MPs is one of the most important factors in choosing a sensing technique.

Quantitatively resolving multivalent interactions on a macroscopic scale using force spectroscopy

Multivalent interactions remain difficult to be characterized and consequently controlled, particularly on a macroscopic scale. Using force-induced remnant magnetization spectroscopy (FIRMS), we have resolved the single-, double-, and triple-biotin-streptavidin interactions, multivalent DNA interactions and CXCL12-CXCR4 interactions on millimetre-scale surfaces. Our results establish FIRMS as a viable method for systematic resolution and controlled formation of multivalent interactions.

Mechanically resolving noncovalent bonds using acoustic radiation force

The resolution of molecular bonds and subsequent selective control of their binding are of great significance in chemistry and biology. We have developed a method based on the use of acoustic radiation force to precisely dissociate noncovalent molecular bonds. The acoustic radiation force is produced by extremely low-power ultrasound waves and is mediated by magnetic particles. We successfully distinguished the binding of antibodies of different subclasses and the binding of DNA duplexes with a single-base-pair difference. In contrast to most ultrasound applications in chemistry, the sonication probe is noninvasive and requires a sample volume of only a few microliters. Our method is thus viable for noninvasive and accurate control of molecular bonds that are widely encountered in biochemistry.