Functionalization of Silicon Nanowires with Actomyosin Motor Protein for Bioinspired Nanomechanical Applications

Abstract

Motor proteins generate motions in a biological system by converting the chemical energy of adenosine triphosphate (ATP) into mechanical energy. Actin filament/myosin (actomyosin) is a well-studied example, and it performs essential functions in biological systems, such as muscle contraction, organelle transport, and cell motility. [1] A common experimental scheme to study motor proteins is a gliding assay on glass substrates, where the motions of actin filaments are analyzed on randomly distributed myosin on two-dimensional (2D) substrates. [1] In this case, the actin filaments exhibited rather disordered motions close to a 2D random walk, which is somewhat different to that in vivo systems. In muscle cells, myosin goes through one-dimensional (1D) motion on straight actin filaments. Many researchers have tried to build narrow myosin patterns or guiding channels to imitate 1D in vivo systems. [2][3][4][5][6][7][8][9] However, previous strategies have often suffered from various limitations. For example, the guiding barriers used to confine actin filaments in 1D trajectories can disturb the natural motion of actomyosin. Without guiding barriers, actin filaments can easily leave the narrow myosin patterns. On the other hand, motor proteins have been actively investigated for protein-based nanomechanical systems due to their high fuel efficiency and large force generation. For such applications, one should be able to combine motor proteins with inorganic components, such as nanostructures. [10][11][12][13][14][15][16][17][18][19] However, the assembly method of myosin motor protein with 1D rigid nanostructures (e.g., nanowires, etc.) has not been reported yet, which is the major problem that we would like to solve in this investigation.In this Communication, we report a method to functionalize silicon nanowires (Si-NWs) with heavy meromyosin (HMM), the double-headed myosin motor domain, and to disperse the resulting HMM-functionalized Si-NWs in aqueous solution. In this approach, Si-NWs were first functionalized with amine chemical groups, and the assembly of HMM was directed onto the Si-NWs in the solution. Furthermore, we successfully demonstrated 1D motility assay on the functionalized Si-NWs, where the motion of actin filaments was confined on the 100-nm-diameter Si-NWs without any confining physical barriers. Significantly, the HMM-functionalized Si-NWs successfully supported the continuous motility of actin filaments over a 100-mm-long distance, enabling stable 1D motility assay. We introduced Flory's characteristic ratio with randomwalk theory to analyze the motion of actin filaments on HMM-functionalized Si-NWs and glass substrates. [20] The results revealed that actomyosin undergoes ballistic and superdiffusive motion on 1D Si-NWs and 2D glass substrates, respectively. These HMM-functionalized Si-NWs could be an ideal platform for 1D motor protein assay and various nanomechanical applications. Figure 1A shows a schematic diagram depicting the experimental procedure. The ultralong Si-NWs (over 100 mm in len...

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