Polymer-membrane interaction, conformational transitions and soft mode instabilities

Wokyung Sung
2000 AIP Conference Proceedings  
The biopolymers and membranes constitute the basic structures of the biological systems in mesoscopic level. Due to flexibility combined with low dimensionality in their primary structures, they tend to be susceptible to thermal fluctuation and thus undergo conformational transitions relevant to biological functions. In this vein, I will review our recent studies of conformational transitions and instabilities in the interacting systems of a polymer and a membrane, including a semiflexible
more » ... a semiflexible polymer on a surface, a model membrane-bound protein conformations, membrane budding and encapsulation by an adsorbed polymer, and soft mode instability of membranes. The central themes of the paper are soft matter flexibility and connectivity that can give rise to a variety of conformational change and cooperativity. The biological systems in cellular level are mainly composed of biopolymers such as DNA, RNA and proteins, and membranes [1]. On a mesoscopic length scale, the polymers and membranes represent the one and two dimensional soft matter in their primary structures. Due to their low dimensionality and flexibility, thermal fluctuation plays important roles in affecting their conformations. The conformational transitions and the shape changes arising from the polymer-membrane interaction are relevant to various biological functions in cells. A well-known example of the conformational transitions of a polymer interacting with an attracting surface is binding-unbinding transition. When a polymer is brought into attractive interaction with a membrane, it undergoes reductions in the internal energy (AJ5? < 0), and in the conformational entropy (AS < 0) as well due to the confinement. Depending upon the competitions between these two factors, binding (adsorption) or unbinding (desorption) would occur. When the intercation dominates over entropy, the free energy change AF = A£" -TAS is negative, leading to polymer adsorption below a critical temperature T c -(/\E/AS)^F =0 . When the free energy change is positive, the polymer will desorb above the critical temperature. The binding-unbinding transition is indeed an outcome of conformational flexibility and fluctuation unique to soft matter. CP519, Statistical Physics, edited by M. Tokuyama and H. E. Stanley
doi:10.1063/1.1291602 fatcat:dhlcu4wllvfkhgfalrj5fog4ya