Enhanced polymerization of polar macromolecules by an applied electric field with application to mitosis

Numerous cellular processes are characterized by the rapid polymerization of protein molecules to form rod-like structures. Examples include the formation of spindle fibers from tubulin during cell division and the polymerization of actin into the actin filaments of the pseudopod in chemotaxis. It has been proposed that these proteins possess an electric dipole moment and that the onset of an internal electric field triggers polymerization. In this theoretical study, the relative probability of polymerization of a polar protein species is calculated in the presence and absence of an electric field. There is a significant enhancement of polymerization in the presence of an electric field, which increases as the size of the attachment site decreases. We conclude that a cytoplasmic pool of suitable proteins will rapidly polymerize if an electric field is applied, while remaining in a random configuration in the absence of a field. This mechanism is applied to the mitotic spindle structure, and by assuming that the spindle poles become oppositely charged during mitosis, a finite difference method is used to calculate the spindle structure at metaphase. Good agreement is obtained with experiment data.