Cytoskeletal structure of Mycoplasma mobile
Mycoplasma mobile, a parasitic bacterium lacking a peptidoglycan layer, glides on solid surfaces in the direction of a membrane protrusion at a cell pole by a unique mechanism. The mechanism supporting the strong force generated by the gliding machinery of M. mobile has been unexplained. Recently, a working model was proposed in which cells are propelled by leg proteins clustering at the protrusion’s base. The legs repeatedly catch and release sialic acids on the solid surface, a motion that is driven by the force generated by ATP hydrolysis. This paper proposes of a structural model, the cytoskeletal jellyfish structure, which is distinct from any other bacterial cytoskeleton. The researchers stripped the cell membrane using the detergent Triton X-100 and identified a unique structure, designated the “jellyfish” structure. In this structure, an oval solid “bell” approximately 235 nm wide and 155 nm long is filled with a 12-nm hexagonal lattice and connected to this structure are dozens of flexible “tentacles” that are covered with particles of 20 nm diameter at intervals of approximately 30 nm. The particles appear to have 180 rotational symmetry and a dimple at the center. The relation of this structure to the gliding mechanism was suggested by its cellular localization and by analyses of mutants lacking proteins essential for gliding. They identified 10 proteins as the components by mass spectrometry and found that these do not show sequence similarities with other proteins of bacterial cytoskeletons or the gliding proteins previously identified. It is hoped that this structure will shed light on our understanding of the bacterial cytoskeletons and their evolution.
Cytoskeletal “jellyfish” structure of Mycoplasma mobile. PNAS USA 2007 Nov 27
Tags: Bacteria, Biology, Microbiology, Science
