'WET' ELECTROSTATICS AND BIOMOLECULAR SELF-ASSEMBLY

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 'Wet' electrostatic interactions are poorly understood and often exhibit counterintuitive behavior. For example, two like-charged macromolecules in aqueous solution are expected to repel one another, which is essentially the prediction of prevailing mean-field theories. In the presence of multivalent ions, however, many biopolymers actually attract one another and condense into compact, ordered states. Examples include DNA condensation by charged histones in chromosomes, and DNA packaging by multivalent protamines in bacteria and viral capsids. In our previous work at SSRL, we have directly observed a molecular mechanism for attractions between rod-like polyelectrolytes by observing counterion organization. The aim of the present proposed program is to develop our intuition for more complex forms of electrostatic assembly. We will examine a series of paradigmatic examples of interactions between simple geometric objects, such as complexes formed between like-charged rods and sheets (anionic DNA and anionic membranes), or complexes formed between oppositely charged rods and spheroids (F-actin and monodisperse cationic globular proteins (lysozyme, lactoferrin)) in the presence of salts of different valence. In particular, we will take advantage of genetic engineering techniques to make mutant proteins with essentially the same size but with different net charges and charge distributions, and examine how these changes impinge on their self-assembly behavior.