FW: [Perspective] How Shape Affects Microtubule and Nanoparticle Assembly

[Description: Figure]

It is quite interesting to observe the change of shapes under some stimulus for better structures and functions.

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Part of the tantalizing promise of nanoparticles is that they can serve as building blocks of complex systems that could outperform other materials. For example, different structures could form depending on the shape of the nanoparticles. A stimulus, such as a change in temperature or the addition of a small molecule, that changes nanoparticle shape could create a new structure with a different function. Nature provides a large example set of nanoparticles in the form of proteins, which can be studied to gain insight into shape-dependent assembly. In a recent paper, Ojeda-Lopez et al. (1<http://www.sciencemag.org/content/343/6174/981.full#ref-1>) describe a new shape-changing mechanism that dramatically alters how a protein system assembles. The α–β tubulin dimer naturally polymerizes to form microtubules. The authors discovered that adding a highly charged small molecule, spermine, causes a shape transformation. The tubules assemble within an inverted structure compared to that of the original microtubules.
Microtubules, the track along which kinesin motor proteins walk, are a key component underlying cellular transport and cell division (2<http://www.sciencemag.org/content/343/6174/981.full#ref-2>). These functions occur in part because of the special properties derived from tubulin, which are of interest to general polymer physics and to the development of synthetic systems, such as ones performing nanoscale transport (3<http://www.sciencemag.org/content/343/6174/981.full#ref-3>). Microtubules assemble, dissociate, and reassemble in cells, and the dynamics of polymerization and depolymerization depends on binding of guanosine triphosphate (GTP) and its dephosphorylation to guanosine diphosphate (GDP). With GTP bound to tubulin, straight growth of the tubule occurs, but the transition to GDP alters the tubulin geometry, tending to cause filaments to peel away in arcs, and leads to catastrophic depolymerization.
Ojeda-Lopez et al. stabilized the microtubules using taxol. The subsequent addition of spermine produced arcs peeling away from the tubule, similar to the effect of dephosphorylation (see the figure). However, the spermine-induced structure is an inverted tubulin tubule (ITT)—a spiral tubule with tubulin orientation inverted with respect to the microtubule orientation. The ITT has a larger diameter, 40 nm, versus 24 nm for microtubules.


Feed: Science: Current Issue
Posted on: Friday, 28 February 2014 11:00 AM
Author: Mark J. Stevens
Subject: [Perspective] How Shape Affects Microtubule and Nanoparticle Assembly

Models of nanoparticle assembly can help explain aspects of the inverted structure that forms because of induced change in tubulin protein shape. Author: Mark J. Stevens


View article...<http://www.sciencemag.org/content/343/6174/981.abstract?rss=1>