Supporting Images for "Nano Springs Eternal"
News from the ASCB 45th Annual Meeting
San Francisco, CA | December 10-14, 2005
D. C. France , V. Baru , M. Shribak , S. Inoue , S. McCutcheon, H. E. Buhse , P. T. Matsudaira [1,2,5]
 Biological Engineering at the Massachusetts Institute of Technology, Cambridge, MA
 Whitehead Institute for Biomedical Research, Cambridge, MA
 Marine Biological Laboratory, Woods Hole, MA
 Biological Sciences at the University of Illinois at Chicago, Chicago, IL
 Biology at the Massachusetts Institute of Technology, Cambridge, MA
A Centrin-based Cellular Spring that Generates nNs of Force
The spasmoneme of the unicellular protozooan Vorticella convallaria is among the fastest and most powerful cellular engines known. A contractile organelle that uses calcium instead of ATP for energy, the spasmoneme is a bundle of fibers of undetermined composition. Centrin is the major component by dry-weight and the active calcium-binding element. Also found in filamentous structures associated with various actions ranging from spindle pole and centrosome movements to contraction of whole cell bodies, centrin may be the basis of a fourth cytoskeleton. To understand how centrin-based systems are involved in cell motility, we have been characterizing the structure, mechanics, and biochemistry of the spasmoneme and report several novel findings. First, the spasmoneme is a powerful cellular engine. We imaged spontaneous contractions while imposing a centrifugal force load on the cell body. At accelerations over 10000g, the cell body becomes tear-drop shaped, its contents become stratified, and yet the stalk still contracts. We estimate an upper bound on the amount of force generated during contraction in excess of 200 nN. Second, the current rubber-band model of the spasmoneme relies on a previously observed loss of spasmoneme birefringence in the contracted state, as oriented, birefringent fibers become disoriented with added calcium. In contrast, images from the orientation-independent polarized light microscope (LCPolScope) show the spasmoneme consists of fibers that retain some degree of order in the contracted state. Finally, we are able to correlate the structure and mechanics of the spasmoneme directly with centrin. After extracting the stalks under conditions which retain reversible calcium-dependent contractility, we find that one anti-Vorticella centrin antibody (anti-centrin 5) abolishes contractility while another (anti-centrin 4) does not. These observations suggest that the spasmoneme is a centrin-based mechanism that is unlike any actin or microtubule-based cellular engine, yet more powerful.
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