Intra-cellular active transport by native cargos is ubiquitous. We investigate the motion of spherical nano-particles (NPs) grafted with flexible polymers that end with a nuclear localization signal peptide. This peptide allows the recruitment of several mammalian dynein motors from cytoplasmic extracts. To determine how motor–motor interactions influenced motility on the single microtubule level, we conducted bead-motility assays incorporating surface adsorbed microtubules and combined them with model simulations that were based on the properties of a single dynein. The experimental and simulation results revealed long time trajectories: when the number of NP-ligated motors Nm increased, run-times and run-lengths were enhanced and mean velocities were somewhat decreased. Moreover, the dependence of the velocity on run-time followed a universal curve, regardless of the system composition. Model simulations also demonstrated left- and right-handed helical motion and revealed self-regulation of the number of microtubule-bound, actively transporting dynein motors. This number was stochastic along trajectories and was distributed mainly between one, two, and three motors, regardless of Nm. We propose that this self-regulation allows our synthetic NPs to achieve persistent motion that is associated with major helicity. Such a helical motion might affect obstacle bypassing, which can influence active transport efficiency when facing the crowded environment of the cell.

No abstract

Targeting the cell nucleus remains a challenge for drug delivery. Here we present a universal platform for smart design of nano-particles (NPs) decoration that allows recruitment of multiple dynein motors to drive their active motion towards the nucleus. The uniqueness of our approach is based on using: (i) a spacer polymer, commonly Biotin-Polyethylene-glycol-thiol (B-PEG-SH), whose grafting density and molecular weight can be tuned thereby allowing NP transport optimization, and (ii) protein binding peptides, like cell penetrating, NLS, or cancer targeting, peptides. Universal chemistry is employed to link peptides to the PEG free-end. To manifest our platform, we use a SV40T large antigen-originating NLS peptide. Our modular design allows tuning the number of recruited motors, and to replace the NLS by a variety of other localization signal molecules. Our control of the NP decoration scheme, and the modularity of our platform, carries great advantage for nano-carrier design for drug delivery applications.

The ESCRT machinery mediate membrane remodeling in numerous processes in cells including cell division and nuclear membrane reformation. The identification of ESCRT homologs in Asgard archaea, currently considered the closest ancestor of eukaryotes, suggests a role for ESCRTs in the membrane remodeling processes that occurred during eukaryogenesis. Yet, the function of these distant ESCRT homologs is mostly unresolved. Here we show that Asgard ESCRT-III proteins self-assemble into homo- and hetero- helical tubes, a hallmark of the eukaryotic ESCRT system. Asgard ESCRT-III tube assembly was facilitated in the presence of DNA and inhibited by DNAase. Notably, Asgard ESCRT-III filaments remodeled eukaryotic-like membrane vesicles, also in the presence of DNA, indicating an ancient role for the ESCRT complex in membrane remodeling, that may involve DNA binding. The ability of Asgard archaeal ESCRTs to remodel eukaryotic-like membranes, places them at the junction between prokaryotes and eukaryotes, substantiating a role for ESCRTs in eukaryogenesis

Native cargos achieve efficient intra-cellular active transport by recruiting multiple motors proteins from the cytoplasm. Here we investigate the motion of spherical nano-particles (NPs), acting as model cargos, grafted with flexible polymers, each ending with a nuclear localization signal (NLS) peptide, thereby allowing recruitment of mammalian cytoplasmic dynein. Bead-motility assays show several unique features. As the number of motors increases, the run-time and run-length increase, the longitudinal velocity mean decreases, whereas its width shows a non-monotonous behavior. Moreover, both single and multi-motor NPs perform angular (i.e., projected transverse) motion. Strikingly, the directions of angular and longitudinal motions are correlated, such that retrograde steps are combined with right-handed motion. We formulate a theoretical model to simulate the multi-dynein transported NP. The model builds on a recently theoretical description of single yeast dynein stepping on the curved microtubule surface, modified to account for mammalian dynein, and generalized to include motor-motor elastic and excluded-volume coupling. The simulation results are majorly in agreement with our experimental results. Moreover, long time trajectories exhibit both left- and right- handed helical motion around the MT symmetry axis, consistent with the measured and simulated angular velocity. The model gives further insight into the mechanism of the NP motion and suggests that the NPs are self-regulating the number of participating motors, optimizing between single motor, for obstacle bypassing, and multi-motor behavior, for persistent directional motion. We suggest that native cargos could use a similar mechanism to achieve efficient transport in the crowded cellular environment.