Highlights d Proteins transiently binding to dynamic microtubule ends can drive cargo motility d Dynamic microtubules can remodel membranes through tipattachment complexes (TACs) d An EB protein and its membrane-bound partner are sufficient to form a TAC d TACs and motor proteins can cooperate to extend membrane tubes Authors Ruddi Rodrı ´guez-Garcı ´a,

We present a systematic study in investigating the orientation characteristics of pentacene molecules grown on graphene substrates using polarized Raman spectroscopy. The substrate-induced orientation alignment of pentacene can be well distinguished through the polarized Raman spectra. Interestingly, we found that the nature of polycrystalline graphene not only provides efficient route to control molecular orientation, but also acts as an excellent template allowing conjugated molecules to stack accordingly. The relative orientation of the well-aligned pentacene molecules and the nearby graphene domains exhibits several preferred angles due to atomic interactions. This unique feature is further examined and verified by single domain graphene. Furthermore, polarized Raman spectroscopy contains abundant information allowing us to analyze the ordering level of pentacene films with various thicknesses, which provides insightful perspectives of manipulating molecular orientations with graphene and spatial organization between conjugated systems, in a more quantitative manner.

Force generation by molecular motors drives biological processes such as asymmetric cell division and cell migration. Microtubule gliding assays in which surface-immobilized motor proteins drive microtubule propulsion are widely used to study basic motor properties as well as the collective behavior of active self-organized systems. Additionally, these assays can be employed for nanotechnological applications such as analyte detection, biocomputation, and mechanical sensing. While such assays allow tight control over the experimental conditions, spatiotemporal control of force generation has remained underdeveloped. Here we use light-inducible protein–protein interactions to recruit molecular motors to the surface to control microtubule gliding activity in vitro. We show that using these light-inducible interactions, proteins can be recruited to the surface in patterns, reaching a ∼5-fold enrichment within 6 s upon illumination. Subsequently, proteins are released with a half-life of 13 s when the illumination is stopped. We furthermore demonstrate that light-controlled kinesin recruitment results in reversible activation of microtubule gliding along the surface, enabling efficient control over local microtubule motility. Our approach to locally control force generation offers a way to study the effects of nonuniform pulling forces on different microtubule arrays and also provides novel strategies for local control in nanotechnological applications.

Microtubule-dependent organization of membrane organelles, such as the endoplasmic reticulum, occurs through motor-based pulling and by coupling polymer dynamics to membrane remodeling. Membrane binding to dynamic microtubule ends involves transient interactions, but how such interactions can lead to membrane deformation is unclear.Here, we reconstitute membrane tubulation in a minimal system with giant unilamellar vesicles, dynamic microtubules, End-Binding (EB) proteins and a membrane-targeted polypeptide that interacts with EBs and microtubules. We demonstrate that these components are sufficient to induce not only membrane tubulation by growing microtubule ends, but also motor-independent membrane sliding along microtubule shafts and tube pulling by shrinking microtubules. Experiments and modeling reveal that the first two mechanisms can be explained by adhesion-driven biased membrane spreading on microtubules. Attachments to growing and shrinking microtubule ends can sustain forces of ~0.5 and ~5 pN, respectively. Rapidly exchanging molecules that connect membranes to dynamic microtubules can thus induce membrane tubulation and processive tube motility. 7 linked to membranes can promote some membrane tubulation, but the generation of long membrane tubes occurs much more efficiently when an EB3 protein is combined with a MT-binding membrane-attached peptide. MT-dependent membrane tubulation is limited by tensionPrevious studies have shown that ligand-dependent adhesion of GUVs to the surface of a solid substrate or to a nanofiber triggered the formation of membrane tubules 37-39 . When a GUV faces an adhesive substrate in the presence of mobile ligands, the ligands that bind to the substrate move to the contact region and increase the adhesion strength 40, 41 . We investigated whether His-GFP-SxIP was enriched in the regions where GUVs interacted with MTs and found that the average fluorescence intensity of the His-GFP-SxIP on MTs bound to the membrane was indeed higher than on free MTs or membranes that were not in contact with MTs (Fig. 3a,b). His-GFP-SxIP proteins thus converged towards the sites of MT-membrane contact, suggesting an increase in the number of bonds between the two structures.Next, we investigated the dynamics of formation of tubular membrane networks by measuring GUV sphericity 36 over time. At the beginning of the assay, sphericity quickly decreased, indicating that the network of membrane tubes rapidly expanded (Fig. 3c,d). At later time points, the sphericity value became almost constant as tube extension slowed down ( Fig. 3c,d, and Supplementary Video 1). We hypothesized that this was caused by the increase in lateral tension after the excess of membrane area was used up due to membrane redistribution into tubes [42][43][44][45] . To test this possibility, we characterized thermal membrane fluctuations, which are controlled by the balance between thermal energy, lateral tension and membrane stiffness 4, 5 . Flickering spectroscopy 46, 47 was used to analyze membrane undulations in fre...