Torsion Profiling of Proteins Using Magnetic Particles

Abstract

We report a method to profile the torsional spring properties of proteins as a function of the angle of rotation. The torque is applied by superparamagnetic particles and has been calibrated while taking account of the magnetization dynamics of the particles. We record and compare the torsional profiles of single Protein G-Immunoglobulin G (IgG) and IgG-IgG complexes, sandwiched between a substrate and a superparamagnetic particle, for torques in the range between 0.5 × 10(3) and 5 × 10(3) pN·nm. Both molecular systems show torsional stiffening for increasing rotation angle, but the elastic and inelastic torsion stiffnesses are remarkably different. We interpret the results in terms of the structural properties of the molecules. The torsion profiling technique opens new dimensions for research on biomolecular characterization and for research on bio-nanomechanical structure-function relationships.

Rotating magnetic particles for lab-on-chip applications – a comprehensive review

“…1 pN using a 1 μm arm). 70 Superparamagnetic micrometer-sized multicore MPs, like the ones invented by John Ugelstad et al, 99 typically contain tens of thousands of non-remnant nanometer-sized cores fixed in a non-magnetic matrix. If these cores are randomly oriented, one would expect an isotropic magnetic susceptibility and thus it would be impossible to generate a magnetic torque.…”

“…54,55 Later, eMTTs were also used to study single biological molecules. 70 Typically a single coil or a set of two coils is used to control the magnetic field amplitude along a single axis. By adding pairs of coils, field control is extended to two or three spatial dimensions.…”

Biological Magnetometry: Torque on Superparamagnetic Beads in Magnetic Fields

“…(2)], i.e., on expð−F=k B TÞ [27][28][29][30][31][32][33][34]. Finally, a recently proposed model [8] simplifies the SW model by reducing the continuous range of θ 1 to just two orientations aligned with the anisotropy axis ("two-stateflipping," 2SF), i.e., θ 1 ¼ nπ, where n is an integer. Flipping between these orientations requires an external magnetic fieldB to overcome the coercive fieldB coercive of the NP, i.e., provided jBj > jB coercive j, θ 2 ¼ θ NP − nπ To quantitatively probe the torque response of commercially available superparamagnetic beads commonly used in MT measurements, we followed two complementary experimental strategies.…”

“…In contrast, there is currently no well-accepted theory to predict the torque on superparamagnetic beads inside an external field. A predictive understanding of the magnetic torque would be desirable, considering the increasing use of magnetic beads to apply and measure torque and twist [3,[8][9][10][11][12][13].…”

Modular, ultra-stable, and highly parallel protein force spectroscopy in magnetic tweezers using peptide linkers

“…titin Ig or protein L domains (21)(22)(23)(24). Current strategies for attaching proteins to the surface in MT are either based on antibodies (25)(26)(27)(28)(29) or His-tag Cu 2+ -NTA chemistry (30,31), or on covalent linkage, either of Halo-tag fusion proteins to a surface coated with Halo-tag amine ligands (21)(22)(23)32) or using the Spytag-SpyCatcher system (24,33). Non-covalent attachment has the disadvantage of limited force stability compared to covalent attachment.…”