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标题：Transport efficiency of membrane-anchored kinesin-1 motors depends on motor density and diffusivity
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作者：Rahul Grover ; Janine Fischer ; Friedrich W. Schwarz 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：46
页码：E7185-E7193
DOI：10.1073/pnas.1611398113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceMolecular motors, such as kinesin-1, are essential molecules involved in active intracellular transport. Current mechanistic insights on transport by motors are mainly based on in vitro studies where the motors are bound to rigid substrates. However, when transporting membranous cargo under physiological conditions, multiple motors are often only loosely coupled via a lipid bilayer. In this study, we investigate how the motors transport efficiency is affected when bound to a lipid bilayer. In our reconstituted gliding motility assays, we show that membrane-anchored motors exhibit reduced transport efficiency due to slippage in the lipid bilayer. Notably, the efficiency increases at higher motor density and reduced membrane diffusivity, providing cells with an additional means of regulating the efficiency of cargo transport. In eukaryotic cells, membranous vesicles and organelles are transported by ensembles of motor proteins. These motors, such as kinesin-1, have been well characterized in vitro as single molecules or as ensembles rigidly attached to nonbiological substrates. However, the collective transport by membrane-anchored motors, that is, motors attached to a fluid lipid bilayer, is poorly understood. Here, we investigate the influence of motors anchorage to a lipid bilayer on the collective transport characteristics. We reconstituted "membrane-anchored" gliding motility assays using truncated kinesin-1 motors with a streptavidin-binding peptide tag that can attach to streptavidin-loaded, supported lipid bilayers. We found that the diffusing kinesin-1 motors propelled the microtubules in the presence of ATP. Notably, we found the gliding velocity of the microtubules to be strongly dependent on the number of motors and their diffusivity in the lipid bilayer. The microtubule gliding velocity increased with increasing motor density and membrane viscosity, reaching up to the stepping velocity of single motors. This finding is in contrast to conventional gliding motility assays where the density of surface-immobilized kinesin-1 motors does not influence the microtubule velocity over a wide range. We reason that the transport efficiency of membrane-anchored motors is reduced because of their slippage in the lipid bilayer, an effect that we directly observed using single-molecule fluorescence microscopy. Our results illustrate the importance of motor-cargo coupling, which potentially provides cells with an additional means of regulating the efficiency of cargo transport.
关键词：molecular motors ; lipid bilayers ; transport efficiency ; motor-cargo coupling ; streptavidin-binding peptide