Abstract
MreB, a major component of the bacterial cytoskeleton, exhibits high structural homology to its eukaryotic counterpart actin. Live cell microscopy studies suggest that MreB molecules organize into large filamentous spirals that support the cell membrane and play a key shape-determining function. However, the basic properties of MreB filament assembly remain unknown. Here, we studied the assembly of Thermotoga maritima MreB triggered by ATP in vitro and compared it to the well-studied assembly of actin. These studies show that MreB filament ultrastructure and polymerization depend crucially on temperature as well as the ions present on solution. At the optimal growth temperature of T. maritima, MreB assembly proceeded much faster than that of actin, without nucleation (or nucleation is highly favorable and fast) and with little or no contribution from filament end-to-end annealing. MreB exhibited rates of ATP hydrolysis and phosphate release similar to that of F-actin, however, with a critical concentration of approximately 3 nm, which is approximately 100-fold lower than that of actin. Furthermore, MreB assembled into filamentous bundles that have the ability to spontaneously form ring-like structures without auxiliary proteins. These findings suggest that despite high structural homology, MreB and actin display significantly different assembly properties.
Highlights
The existence of an extended bacterial cytoskeleton was in doubt until recently
Live cell microscopy studies show that MreB molecules assemble into large filamentous spirals that lie under the cell membrane and span the cell length [2,3,4]
The Polymerization of T. maritima MreB Is Temperature-dependent—T. maritima performs its biological function in a high temperature environment [19, 25]; we studied the effect of temperature on the polymerization of MreB
Summary
The existence of an extended bacterial cytoskeleton was in doubt until recently. The discovery of intracellular filamentous protein assemblies with cell shape-defining functions has changed our view of the bacterium subcellular organization. Based on homology in amino acid sequences, several bacterial proteins are believed to belong to the actin family. Among the known actin-like bacterial proteins, MreB is the most homologous to actin in amino acid sequence, structure, and size [1]. While the in vivo functions of MreB are being actively explored, remarkably little is known about its mechanism of assembly It is unknown whether MreB assembly is faster than F-actin assembly given the typically much shorter lifecycle of bacteria compared with mammalian cells. Using multiple-angle light scattering, we assessed in real time the rigidity and ultrastructure of MreB in solution during assembly These light scattering studies were complemented by electron microscopy (EM) imaging of MreB filamentous structures. These studies suggest that MreB catalyzes ATP hydrolysis and releases phosphate (Pi) at a rate similar to that of F-actin
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
