Surface Hydrophobicity Modulates the Operation of Actomyosin-Based Dynamic Nanodevices

Abstract

We studied the impact of surface hydrophobicity on the motility of actin filaments moving on heavy-meromyosin (HMM)-coated surfaces. Apart from nitrocellulose (NC), which is the current standard for motility assays, all materials tested are good candidates for microfabrication: hydrophilic and hydrophobic glass, poly(methyl methacrylate) (PMMA), poly(tert-butyl methacrylate) (PtBuMA), and a copolymer of O-acryloyl acetophenone oxime with a 4-acryloyloxybenzophenone (AAPO). The most hydrophilic (hydrophilic glass, contact angle 35 degrees) and the most hydrophobic (PtBuMA, contact angle 78 degrees) surfaces do not maintain the motility of actin filaments, presumably because of the low density of adsorbed HMM protein or its high levels of denaturation, respectively. The velocity of actin filaments presents higher values in the middle of this "surface hydrophobicity motility window" (NC, PMMA), and a bimodal distribution, which is more apparent at the edges of this motility window (hydrophobic glass and AAPO). A molecular surface analysis of HMM and its S1 units suggests that the two very different, temporally separated conformations of the HMM heads could exacerbate the surface-modulated protein behavior, which is common to all microdevices using surface-immobilized proteins. An explanation for the above behavior proposes that the motility of actin filaments on HMM-functionalized surfaces is the result of the action of three populations of motors, each in a different surface-protein conformation, that is, HMM with both heads working (high velocities), working with one head (low velocities), and fully denatured HMM (no motility). It is also proposed that the molecularly dynamic nature of polymer surfaces amplifies the impact of surface hydrophobicity on protein behavior. The study demonstrates that PMMA is a good candidate for the fabrication of future actomyosin-driven dynamic nanodevices because it induces the smoothest motility of individual nano-objects with velocities comparable with those obtained on NC.

Translational actomyosin research: fundamental insights and applications hand in hand

“…The increased sliding velocity for a contact angle up to approximately 80° is broadly consistent with studies by Nicolau et al (2007) who used glass and various polymers for HMM adsorption and found increased velocity with an increase in contact angle up to approximately 70° but a reduction in velocity for higher contact angles. The relationship between velocity and contact angle was however, different in a study (Kolli et al 2010) comparing motility on nitrocellulose (contact angle ~87°), microcontact printed poly(amidoamine) dendrimers (contact angle ~47°) and 3-mercaptopropyl trimethoxysilane (~68°).…”

“…Particularly for high contact angles (>70°) the effects on velocity show appreciable variability. Whereas Nicolau et al (2007) found a decrease in velocity for contact angles >70°, Kolli et al (2010) obtained high-quality motility on nitrocellulose with contact angle >80°. In our studies (unpublished) we have observed reduced velocity in occasional experiments with more extensive silanization and a contact angle beyond 80°.…”

“…Systematic studies with the goal to understand the motor–surface interactions have therefore been performed both for the microtubule–kinesin system (Fischer and Hess 2007; Hiratsuka et al 2001; Kerssemakers et al 2006; Ozeki et al 2009) and for actomyosin (Albet-Torres et al 2007, 2010; Balaz et al 2007; Jaber et al 2003; Månsson et al 2008; Nicolau et al 2007; Persson et al 2010; Sundberg et al 2003, 2006a). …”

High-Resolution Imaging of a Single Gliding Protofilament of Tubulins by HS-AFM

“…To investigate the origin of the low velocity of MTs, we performed gliding assay of MTs by changing the substrate and monitored the MTs under HS-AFM. We demonstrated an in vitro gliding assay on collodion (nitrocellulose) coated mica substrate which is a hydrophobic surface 26 (see experimental section). The velocity of MTs was found ~590 nm s −1 on the collodion coated mica substrate, which is very close to the velocity of MTs on glass observed in a conventional gliding assay under fluorescence microscope 27 .…”

Protein Molecular Surface Mapped at Different Geometrical Resolutions

“…The evolution from single to several globular domains with the increase of the molecular weight of the protein leads to an increase in the roughness of the molecular surface, rather than the change of its overall shape [68]. There are however proteins (not considered here) which exhibit highly elongated shapes, e.g., fibrinogen, but other very large proteins present specialized structures such as coiled coils, e.g., myosin with its very convoluted (and dynamic) shape[69] or the collagen triple helix [67]. Therefore, the difference in the evolution of the decrease of the probed area versus probe radius for proteins with different sizes appears to be the result of either the increased roughness of the molecular surface, or the departure from the globular shape (e.g., for IgG).…”