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One enigma in biology is the generation, sensing and maintenance of membrane curvature. Curvature-mediating proteins have been shown to induce specific membrane shapes by direct insertion and nanoscopic scaffolding, while the cytoskeletal motors exert forces indirectly through microtubule and actin networks. It remains unclear, whether the manifold direct motorprotein–lipid interactions themselves constitute another fundamental route to remodel the membrane shape. Here we show, combining super-resolution-fluorescence microscopy and membrane-reshaping nanoparticles, that curvature-dependent lipid interactions of myosin-VI on its own, remarkably remodel the membrane geometry into dynamic spatial patterns on the nano- to micrometer scale. We propose a quantitative theoretical model that explains this dynamic membrane sculpting mechanism. The emerging route of motorprotein–lipid interactions reshaping membrane morphology by a mechanism of feedback and instability opens up hitherto unexplored avenues of membrane remodelling and links cytoskeletal motors to early events in the sequence of membrane sculpting in eukaryotic cell biology. Curvature-mediating proteins are known to induce specific membrane shapes, but whether motorprotein-lipid interactions remodel membranes too remains unclear. Here authors show that curvature-dependent lipid interactions of myosin-VI remodel the membrane geometry into dynamic spatial patterns., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

The organization of actomyosin networks lies at the center of many types of cellular motility, including cell polarization and collective cell migration during development and morphogenesis. Myosin-IXa is critically involved in these processes. Using total internal reflection fluorescence microscopy, we resolved actin bundles assembled by myosin-IXa. Electron microscopic data revealed that the bundles consisted of highly ordered lattices with parallel actin polarity. The myosin-IXa motor domains aligned across the network, forming cross-links at a repeat distance of precisely 36 nm, matching the helical repeat of actin. Single-particle image processing resolved three distinct conformations of myosin-IXa in the absence of nucleotide. Using cross-correlation of a modeled actomyosin crystal structure, we identified sites of additional mass, which can only be accounted for by the large insert in loop 2 exclusively found in the motor domain of class IX myosins. We show that the large insert in loop 2 binds calmodulin and creates two coordinated actin-binding sites that constrain the actomyosin interactions generating the actin lattices. The actin lattices introduce orientated tracks at specific sites in the cell, which might install platforms allowing Rho-GTPase–activating protein (RhoGAP) activity to be focused at a definite locus. In addition, the lattices might introduce a myosin-related, force-sensing mechanism into the cytoskeleton in cell polarization and collective cell migration.

Myosins are ATPase motor proteins that are activated by and traffic along actin filaments. This large protein family is divided into many classes with different functional properties and specializations for various roles, including membrane anchorage, longer range transport of cargo vesicles or cell signaling.Myosin class VI is unique due to its reversed directionality along actin filaments, moving towards the pointed end, in contrast to almost all other classes, which move towards the barbed end of F-actin. Whilst the directionality is well studied, other characteristics such as activation, cargo and lipid binding or dimerization are not fully understood. Using size exclusion chromatography, titration studies and gliding filament assays we investigated myosin VI backfolding, cargo binding and mechanical activity.Furthermore, we applied electron microscopy and single particle image processing to determine the structural properties of myosin VI in different ionic and nucleotide conditions. Two dimensional class averages based on various alignment and classification methods were made that allow for a detailed structural analysis including a comparison with crystal structures.