Department of Biomedical Engineering, Columbia University , New York, New York 10027, United States.
Department of Biomedical Engineering and Department of Pathology, University of Miami , Coral Gables, Florida 33146, United States.
Langmuir. 2016 Aug 9;32(31):7943-50. doi: 10.1021/acs.langmuir.6b02369. Epub 2016 Jul 26.
Motor proteins such as myosin and kinesin play a major role in cellular cargo transport, muscle contraction, cell division, and engineered nanodevices. Quantifying the collective behavior of coupled motors is critical to our understanding of these systems. An excellent model system is the gliding motility assay, where hundreds of surface-adhered motors propel one cytoskeletal filament such as an actin filament or a microtubule. The filament motion can be observed using fluorescence microscopy, revealing fluctuations in gliding velocity. These velocity fluctuations have been previously quantified by a motional diffusion coefficient, which Sekimoto and Tawada explained as arising from the addition and removal of motors from the linear array of motors propelling the filament as it advances, assuming that different motors are not equally efficient in their force generation. A computational model of kinesin head diffusion and binding to the microtubule allowed us to quantify the heterogeneity of motor efficiency arising from the combination of anharmonic tail stiffness and varying attachment geometries assuming random motor locations on the surface and an absence of coordination between motors. Knowledge of the heterogeneity allows the calculation of the proportionality constant between the motional diffusion coefficient and the motor density. The calculated value (0.3) is within a standard error of our measurements of the motional diffusion coefficient on surfaces with varying motor densities calibrated by landing rate experiments. This allowed us to quantify the loss in efficiency of coupled molecular motors arising from heterogeneity in the attachment geometry.
马达蛋白（如肌球蛋白和驱动蛋白）在细胞货物运输、肌肉收缩、细胞分裂和工程纳米器件中起着重要作用。量化耦合马达的集体行为对于我们理解这些系统至关重要。一个很好的模型系统是滑行运动检测，其中数百个表面附着的马达推动一个细胞骨架丝，如肌动蛋白丝或微管。可以使用荧光显微镜观察细丝运动，揭示滑行速度的波动。先前已经通过运动扩散系数对这些速度波动进行了量化，Sekimoto 和 Tawada 将其解释为由于马达从推进细丝的线性阵列中添加和去除，导致的波动，假设不同的马达在产生力方面的效率不相等。一个关于驱动蛋白头部扩散和与微管结合的计算模型，使我们能够量化由于非谐尾部刚度和不同附着几何形状的组合而产生的马达效率异质性，假设马达在表面上的位置是随机的，并且马达之间没有协调。对异质性的了解允许计算运动扩散系数和马达密度之间的比例常数。计算值（0.3）在我们通过着陆率实验校准的具有不同马达密度的表面上测量运动扩散系数的标准误差范围内。这使我们能够量化由于附着几何形状的异质性而导致的耦合分子马达效率的损失。
