Effects of potential environmental interferents on kinesin-powered molecular shuttles

Spatial Patterning of Kinesin-1 and Dynein Motor Proteins in an In Vitro Assay using Aqueous Two-Phase Systems (ATPS)

Cooperativity of motor proteins is essential for intracellular transport. Although their motion is unidirectional, they often cause bidirectional movement by different types of motors as seen in organelles. However, in vitro assessments of such cellular functions are still inadequate owing to the experimental limitations in precisely patterning multiple motors. Here, we present an approach to immobilize two motor proteins, kinesin-1 and dynein, using the aqueous two-phase system (ATPS) made of poly(ethylene glycol) and dextran polymers. The negligible influence of polymer solutions on the attachment and velocity of motor proteins ensures the compatibility of using ATPS as the patterning technique. The selective fixation of kinesin and dynein was assessed using polarity-marked microtubules (PMMTs). Our experimental results show that on a patterned kinesin surface, 72% of PMMTs display minus-end leading motility, while on a dynein surface, 79% of PMMTs display plus-end leading motility. This work offers a universal and biocompatible method to pattern motor proteins of different classes at the nanoscale, providing a new route to study different cellular functions performed by molecular motors such as the formation of mitotic spindles.

Magnetic Quantum Dots Steer and Detach Microtubules From Kinesin-Coated Surfaces

The microtubule (MT)-kinesin system has been extensively studied because of its role in cellular processes, as well as its potential use for controllably transporting objects at the nanoscale. Thus, there is substantial interest in methods to evaluate MT properties, including bending radius and the binding energy of kinesin motor proteins to MT tracks. Current methods to identify these properties include optical tweezers, microfluidic devices, and magnetic fields. Here, the use of magnetic quantum dots (i.e., MagDots) is evaluated as a method to study MT-kinesin interactions via applied magnetic forces. Magnetic fields are generated using a magnetic needle whose field gradient is quantified by finite element modeling (FEM). Magnetic force is applied to MagDot-labeled MTs and demonstrated sufficient to steer and detach MTs from kinesin-coated surfaces. Taking advantage of the dual-functionality of MagDots, the magnetic force experienced by a single MagDot and the number of MagDots on MTs are determined. The total force exerted on MTs by MagDots is estimated to be ≈0.94-2.47 pN. This approach could potentially be used to interrogate MT properties and MT-kinesin interactions, enhancing our biological understanding of this system and enabling further development of MT shuttles for nanotransport.

Microtubule-based nanomaterials: Exploiting nature's dynamic biopolymers

For more than a decade now, biomolecular systems have served as an inspiration for the development of synthetic nanomaterials and systems that are capable of reproducing many of unique and emergent behaviors of living systems. One intriguing element of such systems may be found in a specialized class of proteins known as biomolecular motors that are capable of performing useful work across multiple length scales through the efficient conversion of chemical energy. Microtubule (MT) filaments may be considered within this context as their dynamic assembly and disassembly dissipate energy, and perform work within the cell. MTs are one of three cytoskeletal filaments in eukaryotic cells, and play critical roles in a range of cellular processes including mitosis and vesicular trafficking. Based on their function, physical attributes, and unique dynamics, MTs also serve as a powerful archetype of a supramolecular filament that underlies and drives multiscale emergent behaviors. In this review, we briefly summarize recent efforts to generate hybrid and composite nanomaterials using MTs as biomolecular scaffolds, as well as computational and synthetic approaches to develop synthetic one-dimensional nanostructures that display the enviable attributes of the natural filaments.

Competitive volumetric bar-chart chip with real-time internal control for point-of-care diagnostics

Point-of-care (POC) testing has become widely used in clinical analysis because of its speed and portability; however, POC tools, such as lateral flow assays, suffer from low specificity, unclear readouts, and susceptibility to environmental and user errors. Herein, we report an ELISA-based competitive volumetric bar-chart chip (CV-chip) that eliminates these limitations. The CV-chip displays the readout in the form of ink bar charts based on direct competition between gases generated by the sample and the internal control. By employing a "competition mode", this platform decreases the potential influence of background resulting from environmental factors and provides visually clear positive or negative results without the requirement of calibration. In addition, the on-chip comparison enables the device to distinguish imperceptible differences (less than 1.3-fold) in human chorionic gonadotropin (hCG) concentrations that are near the cutoff value for pregnancy (∼1.4 ng/mL). We also utilized the ELISA-based CV-chip to successfully detect biomarkers from cancer cells. As a proof-of-concept application in a clinical setting, the CV-chip was employed to evaluate the status of drugs of abuse in 18 patients. For six different drugs, zero false-positive and very few false-negative (<2%) results were reported in more than 100 tests. This new ELISA platform offers a clinical diagnostics tool that is portable and easy to use, and provides improved clarity and sensitivity due to the inclusion of a real-time internal control.