Self-assembly of Charged Biopolymers in Solution

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Andrea Liu is supported jointly by the Theoretical and Computational Chemistry Program and the Materials Theory Program to carry out theoretical research pertaining to stiff biopolymers such as DNA and F-actin. These biopolymer chains are highly negatively charged in aqueous solution, and therefore repel one another strongly. However, both DNA and F-actin can form complexes when multivalent positively-charged ions or cationic crosslinking proteins are added. This research considers how generalized linkers can form complexes with charged biopolymers. The primary objective is to elucidate the structure of dilute aggregates and calculate the phase equilibrium between dilute aggregates, dense bundles, and isolated chains. In addition, the kinetics of bundle formation will be examined in both quiescent and sheared solution. These problems are motivated by biological phenomena such as DNA condensation and self-assembly of actin filament networks and bundles. The physical chemistry in this project is rooted in statistical mechanics, which will allow the identification and exploration of the range of phenomena that can result from a minimal model of charged chains and linkers. The research program is expected to provide a useful vehicle for training research students in numerical and analytical techniques, and for introducing them to biological systems and topics in modern condensed phase physical chemistry. It is known that crosslinked networks of charged filaments form inside cells, and that shearing forces on the cells cause responses that lead to metabolic changes. The understanding of these and other biological applications will be enhanced by this research, which aims to develop simple models that are able to explain a wide range of observable phenomena such as DNA condensation.