| It is well known that the biological molecules exert their normal physiological and biochemical function always in complex or supra-molecules structural states. More and more bio-molecular monomer structures with atomic resolution have been resolved with the help of X-ray crystal diffraction and multiple dimensions NMR. It becomes an urgent and foundmental task for the researchers majoring in life sciences throughout the world to explore the bio-molecules dynamics and the polymerized or assembled molecular complexes attributed to the dynamic process and reveal the inherent relationship between them. Although the theory of dissipative structure and synergetics can help us to qualitatively judge the direction, condition and dynamics of self-organization for bio-molecules complexes, it is difficult to reveal the essential relationship between the molecules dynamics and the relevant functional molecular complexes due to the complicated thermodynamic environment in the living cells.Actin is one of the most abundant proteins in cells, typically consisting of 375 amino acid residues with molecular weight 43 KD or so, and has very important cytologic physiological functions in eukaryotes. Being a major structural component of the cytoskeleton, actin is also a highly conserved protein expressed in most living organisms. Actin exists generally in two styles, one is monomer, globular actin (G-actin), and the other is filamentous actin (F-actin), also called microfilament in general. Actin monomer can be polymerized into long right-handed double helical F-actin induced by Mg2+, K+, Na+, and ATP. Due to its diverse and critical function in all eukaryotes, the molecular structure and physiological function of actin have been important subjects of research in cell and structural biology since its discovery. Not only has the atomic structure of the monomeric G-actin been solved in more than one crystal form, but also the atomic models of the F-actin have been proposed as well based on fiber x-ray diffraction and electron microscopy. Such structural elucidation has played a pivotal role in our understanding of the actin function under various conditions.But little attention is paid to the large-scale and complicated F-actin complex aggregate forming in actin self-organization in simple solution F-buffer in vitro so far, which is thought to reflect the inherited thermodynamic features determined by the primary order structure of G-actin. And actin can also be regarded as a good mode protein for researches on the bio-molecules dynamics and the resultant structural complexes. So the large-scale structures of actin filaments forming in low concentration protein solution via self-organization without any F-actin dynamic interfering factors (such as phalloidin etc.) present in vitro, is preliminarily exploit utilizing the atomic force microscope (AFM) together with transmission electron microscope (TEM). It is found that the G-actin can be polymerized into ordered filamentous structures with different diameters from the slimmest filament of single F-actin to giant filaments in tree-like branches aggregates. The observed polymerized actin filaments, to which the most intense attention is attracted, are discretely distributed and show obvious polymorphism distinctly different from those in the filamentous networks forming in the presence of phalloidin or actin binding proteins (fimbrin, gelsolin, etc.) in previous experiments and the current ones on the negatively stained sample observed by TEM, which are mainly composed of single F-actin and/or multifilaments clearly consisting of several single F-actin. The experimental results clearly demonstrate that non-interference with the F-actin dynamic equilibrium can lead to the polymorphism of actin filamentous structures in self-organizing, and further analysis imply that the disturbance of normal F-actin dynamics by many factors could prevent the emergence of structural polymorphism, more often than not, give rise to formation of specific structures instead and different interferenc... |
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