Minimal requirements for rotation of bacterial flagella.

An in vitro system of cell envelopes from Salmonella typhimurium with functional flagella was used to determine the minimal requirements for flagellar rotation. Rotation in the absence of cytoplasmic constituents could be driven either by respiration or by an artificially imposed chemical gradient of protons. No specific ionic requirements other than protons (or hydroxyls) were found for the motor function.     

The Positively Charged Region of the Myosin IIC Non-helical Tailpiece Promotes Filament Assembly

The motor protein, non-muscle myosin II (NMII), must undergo dynamic oligomerization into filaments to participate in cellular processes such as cell migration and cytokinesis. A small non-helical region at the tail of the long coiled-coil region (tailpiece) is a common feature of all dynamically assembling myosin II proteins. In this study, we investigated the role of the tailpiece in NMII-C self-assembly. We show that the tailpiece is natively unfolded, as seen by circular dichroism and NMR experiments, and is divided into two regions of opposite charge. The positively charged region (Tailpiece_1946–1967) starts at residue 1946 and is extended by seven amino acids at its N terminus from the traditional coiled-coil ending proline (Tailpiece_1953–1967). Pull-down and sedimentation assays showed that the positive Tailpiece_1946–1967 binds to assembly incompetent NMII-C fragments inducing filament assembly. The negative region, residues 1968–2000, is responsible for NMII paracrystal morphology as determined by chimeras in which the negative region was swapped between the NMII isoforms. Mixing the positive and negative peptides had no effect on the ability of the positive peptide to bind and induce filament assembly. This study provides molecular insight into the role of the structurally disordered tailpiece of NMII-C in shifting the oligomeric equilibrium of NMII-C toward filament assembly and determining its morphology.